Homocysteine is an amino acid made from a common dietary amino acid, methionine, that inflicts damage to the inner arterial lining (endothelium). Elevated levels of homocysteine have been associated with many diseases, including:

• cardiovascular disease
• congestive heart failure
• stroke
• migraines
• age-related macular degeneration
• hearing loss
• brain atrophy
• Alzheimer disease

Fortunately, B vitamins like folate, vitamins B₆ and B₁₂, and other integrative interventions can reduce homocysteine and counteract this destructive process.

Causes of High Homocysteine Levels (Hyperhomocysteinemia)

Many factors contribute to high homocysteine levels:

• Insufficient folate, vitamin B₆, vitamin B₁₂, betaine, vitamin B₂, and magnesium
• Certain prescription drugs (including cholestyramine, colestipol, fenofibrate, levodopa, metformin, methotrexate, high-dose niacin, nitrous oxide, pemetrexed, phenytoin, sulfasalazine)
• High-methionine diet (including red meat and dairy products)
• Smoking
• High coffee consumption
• Alcohol consumption
• Advancing age
• Obesity
• Genetic variant that causes an impaired ability to metabolize active folate from folic acid

Note: Life Extension believes that the optimal range for homocysteine levels is <8 µmol/L, much lower than the currently accepted <15 µmol/L.

Dietary and Lifestyle Changes

Several dietary and lifestyle changes can help reduce chronic inflammation:

• Avoid methionine-rich foods like red meat and dairy products
• Exercise, as patients in a cardiac rehabilitation program showed a reduction in homocysteine from exercise alone
• Decrease or eliminate alcohol and smoking

Integrative Interventions

• B vitamins: Folate, along with vitamins B₆ and B₁₂, has been shown in numerous studies to help lower homocysteine levels. The active form of folate, L-methylfolate, can achieve plasma folate levels up to 700% higher than synthetic folic acid and therefore may be more effective at lowering homocysteine levels.
• Betaine (TMG) and choline: Higher intakes of TMG and choline (which is converted to TMG in the body) are related to lower circulating homocysteine concentrations.
• N-acetylcysteine (NAC): NAC may displace homocysteine from its protein carrier, which lowers homocysteine and promotes the formation of cysteine and glutathione, a powerful antioxidant.
• S-adenosylmethionine (SAMe): Supplementing with SAMe promotes the conversion of homocysteine to cysteine, which is then converted to glutathione and lowers homocysteine levels.
• Taurine: Research suggests taurine can block methionine absorption (which is converted to homocysteine in the body) and produce a significant decline in homocysteine levels in 4 weeks.

Homocysteine is an amino acid made in the body through metabolism of the essential amino acid methionine. In healthy circumstances, homocysteine is rapidly broken down, but genetic factors, nutritional inadequacies, certain medications, and some medical conditions can lead to excess homocysteine accumulation, which can damage blood vessels.¹ High homocysteine levels have been correlated with a range of health problems, including atherosclerosis, stroke, neurological diseases, diabetes complications, osteoporosis, depression, erectile dysfunction, and pregnancy complications.^2,3 Although the degree of causality attributable to homocysteine in these conditions is debated, maintaining a healthy homocysteine level is an important part of an overall healthy lifestyle. This is especially true in the context of cardiovascular and neurological health.³

Adequate intake of the B vitamins folate (B₉), cobalamin (B₁₂), pyridoxine (B₆), and riboflavin (B₂) helps facilitate healthy breakdown of homocysteine.¹ People with a genetic propensity for higher homocysteine levels may especially benefit from supplementing with B₂, folate, B₆, and B₁₂.⁴ Omega-3 fatty acids may complement B vitamins in encouraging efficient metabolism of homocysteine.⁵ Betaine (also known as trimethylglycine, or TMG), magnesium, and the trace mineral lithium are also involved in maintaining homocysteine balance.⁶

In this protocol you will learn about methionine metabolism, factors that influence homocysteine regulation, and mechanisms by which excess homocysteine in the blood can cause harm. You will also learn the importance of monitoring homocysteine levels and effective methods for lowering high levels and protecting your long-term health.

Although it is an amino acid, homocysteine is not derived from the diet. Instead, it is made inside cells from the essential dietary amino acid methionine.⁷ This process includes three steps:

1. Methionine to SAMe. Methionine is first converted into S-adenosylmethionine (SAMe) by adding a chemical group called an adenosyl group. SAMe is an important cellular methyl donor: it contains a methyl group that can be transferred to other molecules through methylation reactions. Methylation is critical in biosynthetic processes such as synthesis of DNA, RNA, and many amino acids, proteins, and phospholipids. Methylation is also a critical mechanism for modifying the structure of chromatin, which forms the backbone of deoxyribonucleic acid (DNA)—and which in turn determines how genetic material is expressed. This type of change that regulates gene expression, without changing the genetic code itself, is called epigenetics.
2. SAMe to S-adenosylhomocysteine. When SAMe gives up its methyl group, the result is S-adenosylhomocysteine.
3. S-adenosylhomocysteine to homocysteine. Through removal of the adenosyl group, S-adenosylhomocysteine is converted to homocysteine.

The Fate of Homocysteine

About half of the homocysteine generated in cells is re-methylated, turning it back into methionine.⁸ In most of the body’s cells, this occurs via a folate-dependent pathway, in which a methylated form of folate (5-methyltetrahydofolate, or 5-MTHF) transfers its methyl group to homocysteine. The movement of a methyl group onto and off of folate involves vitamins B₆, B₂, and B₁₂, as well as an important enzyme called methylenetetrahydrofolate reductase, or MTHFR.^1,6,8

Homocysteine can also be re-methylated via a folate-independent pathway, in which betaine (also known as trimethylglycine, or TMG) donates the methyl group to homocysteine. This occurs mainly in liver and kidney cells.^1,6,8

Most of the homocysteine that is not re-methylated is converted to cystathionine via a chemical process called transsulfuration, which requires the amino acid serine, two important enzymes called cystathionine beta-synthase (CBS) and cystathionine gamma-lyase (CSE), and vitamin B6. Cystathionine can then be converted into the amino acid cysteine, or metabolized into energy.⁶ In addition to being used to make proteins, cysteine is also incorporated into the antioxidant glutathione.^18,9

Normally, about 5–10% of the homocysteine generated inside the cells is not metabolized and makes its way into the bloodstream and is subsequently cleared by the kidneys.⁹ However, when either re-methylation or transsulfuration are interrupted, more homocysteine moves out of cells and blood levels rise.⁸

Nutritional and Genetic Causes

Deficiencies of vitamins B₂, B₆, or, more commonly, B₁₂ or folate interrupt re-methylation of homocysteine into methionine. Genetic alterations that result in less-efficient variants of the MTHFR enzyme also prevent sufficient homocysteine re-methylation. Importantly, when homocysteine re-methylation is impaired, SAMe levels fall, leading to a lack of methyl donors for other cell functions.⁸

Homocysteine transsulfuration can be interrupted when vitamin B₆ intake is deficient or in cases of genetic mutations in the code for the CBS enzymes.⁸ The impairment of transsulfuration also leads to dysregulated hydrogen sulfide production.⁹

Other Causes

High homocysteine levels can result from any condition that restricts the availability of nutrients and energy for processing homocysteine. These include^6,10-13:

Smoking High coffee consumption Alcohol consumption Physical inactivity Aging Menopause Diabetes	Psoriasis Hypothyroidism Kidney disease Cancer Digestive disorders Gastrointestinal surgery Exposure to heavy metals (lead, cadmium, mercury, chromium)

In addition, several medications have been implicated in raising homocysteine levels. For example, antacids (H2 blockers such as ranitidine [Zantac] and cimetidine [Tagamet]), proton pump inhibitors (such as omeprazole [Prilosec] and esomeprazole [Nexium]), and metformin (Glucophage) can reduce vitamin B₁₂ absorption and may increase homocysteine levels.¹⁴ The cholesterol-lowering drug fenofibrate (Antara, and others) and the blood pressure-lowering diuretic hydrochlorothiazide (Apo-Hydro, and others) have also been found to raise homocysteine levels.¹⁵

Homocysteine levels are usually measured using a blood test. Typically, the total amount of homocysteine, which includes free and protein-bound homocysteine, is reported.²¹ Total homocysteine levels of 5–14.5 µmol/L are generally considered normal; levels of 15–30 µmol/L are considered mildly elevated; 30–100 µmol/L are intermediately elevated; and levels exceeding 100 µmol/L are seriously elevated.²

Optimal Level

The optimal level for homocysteine remains a topic of debate.⁴⁰ Rather than there being a threshold above which disease occurs, the relationship between homocysteine levels and health may be more continuous.^41-44 For this reason, Life Extension suggests most individuals strive to keep homocysteine levels below 12 µmol/L, with less than 8 µmol/L being considered ideal (although the latter may be difficult for some people to attain).

Early homocysteine research attempting to identify the relationship between homocysteine and health noted that incremental increases in homocysteine levels were accompanied by a higher risk of cardiovascular disease and death.^41,44 In one report from the Hordaland (Norway) Homocysteine Study, 4,766 participants aged 65–67 years had their homocysteine levels measured and were followed for 4.1 years. Compared to participants with homocysteine levels below 9.0 µmol/L, those with levels of 9.0–11.9 µmol/L had a 30% increased risk of cardiovascular death and 40% increased odds of non-cardiovascular death, and those with levels of 12.0–14.9 µmol/L had a 110% increased risk of cardiovascular and 90% increased risk of non-cardiovascular death. Furthermore, the risks were more than two-fold higher in those with levels of 15–19.9 µmol/L and more than three-fold higher in those with levels of 20 µmol/L and above.⁴⁴ In people with coronary artery disease, similar rising trends in risk of hospitalization and death have been associated with incremental increases in homocysteine levels.^42,43 A prospective case-control study of Japanese individuals aged 40 to 85 years found that stroke risk was significantly greater among individuals with homocysteine levels of 11 µmol/L or higher compared with those whose levels were less than 7 µmol/L.⁴⁵

Homocysteine’s relationship with brain health may be similar, and individuals whose homocysteine levels are within the currently accepted normal range may still benefit from homocysteine-lowering therapy. In an eight-year study, participants with baseline homocysteine levels higher than 14.5 µmol/L had nearly twice the risk of Alzheimer disease compared to those with lower levels.⁴⁶ Another study found elderly subjects with homocysteine levels of 10 µmol/L experienced marked cognitive deterioration when levels doubled to 20 µmol/L over 10 years.⁴⁷

A two-year randomized controlled trial assessed the rate of brain atrophy in 168 individuals over age 70 who had mild cognitive impairment and were given a placebo or B-vitamin supplementation (0.8 mg folic acid, 500 mcg B₁₂, and 20 mg B₆) daily. The researchers found that the rate of brain atrophy was considerably slower in the B-vitamin group compared with the control group. Importantly, the treatment response was related to baseline homocysteine levels such that individuals with levels above 13 μmol/L exhibited greater reductions in the rate of brain atrophy with B-vitamin supplementation than those with lower homocysteine levels. The researchers noted that homocysteine-lowering therapy with B vitamins was beneficial in those with baseline homocysteine levels of 9.5 µmol/L or higher.⁴⁸ Furthermore, research from 1997 found that, in healthy men, folic acid supplementation reduced homocysteine levels in all tertiles except the lowest tertile, in which average baseline levels of homocysteine were 7.07 µmol/L.⁴⁹ Cumulatively, these findings suggest supplementation with homocysteine-lowering B vitamins may confer benefits even among individuals whose homocysteine does not exceed normal lab reference ranges.

Genetic variation (polymorphism) fundamentally impacts the activities of enzymes involved in homocysteine metabolism. As a result, some individuals are less efficient at metabolizing homocysteine, and are therefore prone to higher levels, due to genetic factors.

The most widely studied of these polymorphisms as it pertains to homocysteine are those that occur in the MTHFR gene; that is, the gene encoding the folate-metabolizing enzyme methylenetetrahydrofolate reductase (MTHFR). This key enzyme is active in the folate cycle, which, with help from vitamin B₁₂, provides methyl groups for the re-methylation of homocysteine to produce methionine. One common variant, called the TT genotype, affects approximately 10% of the world population.² People with this genotype have lower MTHFR activity, higher homocysteine levels, and a higher risk of cardiovascular and neurological diseases.^50,51 They may be less responsive to folic acid therapy and may require higher supplemental folate doses; they also appear to benefit from supplemental riboflavin (B₂).^4,52,53

A less common but important genetic factor affecting homocysteine metabolism pertains to the CBS gene, which encodes the enzyme cystathionine beta-synthase (CBS). CBS catalyzes the transsulfuration of homocysteine to produce cystathionine. One variant of the CBS gene has been correlated with increased risk of stroke.⁵⁴ A less common mutation of the CBS gene is the cause of a rare genetic disease called homocystinuria, marked by low or no activity of CBS, massive elevation of blood and urine homocysteine levels, and numerous serious complications.⁵⁵

B vitamins are the main therapeutic agents used to treat high homocysteine levels. Many studies confirm their ability, alone and in combinations, to lower high homocysteine levels, and some trials show clinical benefits in the form of reduced risk of stroke and dementia. In general, the combined use of vitamin B₁₂ and folate is more effective than either alone. Benefits of including vitamins B₆ and B₂ in homocysteine-lowering treatment have also been reported.^154,155

Note: In addition to the core approach (B vitamins) described in this section, refer to the Nutrients section later in this Life Extension Protocol for an overview of additional nutritional interventions that may beneficially affect homocysteine metabolism and related pathways.

Vitamin B9: Folate

Reported dosage: 400–5,000 mcg (680–8,500 mcg DFE) per day

Folate, sometimes referred to as vitamin B₉, is found in many plant foods, particularly leafy green vegetables, as well as eggs and liver.¹⁵⁶ Because of its instability, it is often lost or degraded during storage, cooking, and processing.^157,158 Folate deficiency causes a characteristic type of anemia called megaloblastic anemia, which can also be caused by B₁₂ deficiency. Folate deficiency during pregnancy is a well-known cause of neural tube birth defects; in adults, it is associated with neurological disorders including cognitive decline, depression, and neuropathy, as well as Alzheimer and Parkinson diseases.¹⁵⁹ Folic acid is the fully oxidized form of folate. It is a synthetic form of the vitamin that is more stable than folate and is commonly used in supplements and fortification programs.¹⁶⁰ However, L-methylfolate can be an effective alternative to folic acid, with some potential advantages, particularly in people with MTHFR gene variants (see below).

In the United States and a number of other countries, particularly in North and South America, Australia, and New Zealand, folic acid fortification of white flour and cereal grain products is mandatory; and voluntary fortification of various other foods is encouraged as a measure to prevent neural tube birth defects.^160-162 Folic acid fortification was implemented in the United States in 1996, with full implementation essentially completed in late 1997. After the initiation of folic acid fortification, mean plasma folate concentrations increased from 4.6 to 10 ng/mL, homocysteine concentrations fell from 10.1 to 9.4 µmol/L, and the prevalence of homocysteine levels above 13 μmol/L dropped from about 19% to about 10%. The prevalence of low folate concentrations also decreased from 22% to 2%.¹⁶³ As of 2023, 32% of the world’s population lived in regions with mandatory folic acid fortification programs, 53% lived in countries with only voluntary programs, and 15% lived in regions without any folic acid fortification programs. Mandatory folic acid fortification has been associated with higher population-wide folate levels, as well as reduced prevalence of neural tube defects, while voluntary programs have been somewhat less effective.¹⁶²

Certain people continue to be at increased risk of low folate/folic acid intake regardless of fortification programs, such as those on low-carbohydrate diets. In addition, factors that impair folate metabolism can cause functional folate deficiency (deficient folate activity, unrelated to folate intake). These include vitamin B₁₂ deficiency, mutations of the MTHFR gene, and epigenetic modifications that alter expression of other key enzymes involved in folate metabolism.^159,161

Folate is needed to convert homocysteine into methionine. People with low folate levels or impaired ability to use folate have been found to have higher homocysteine levels. Supplementing with folic acid has been shown to reduce homocysteine levels.¹⁵⁹ A meta-analysis of findings from 16 randomized controlled trials found the optimal homocysteine-lowering folic acid dose was around 800 mcg daily. Folic acid in combination with other vitamins, such as 400 mcg folic acid and 400 mcg vitamin B12 or 1,000 mcg of folic acid plus 7.2 mg vitamin B6 and 20 mcg vitamin B12, was also found to reduce homocysteine levels. The trials in the analysis were conducted in countries across the globe, including some with mandatory folic acid fortification programs, like the United States and New Zealand.¹⁵⁵ Likewise, a large clinical trial performed in China (where folic acid fortification is voluntary) tested different doses of folic acid in 2,163 patients with high blood pressure and homocysteine levels of 10 μmol/L or higher and found homocysteine lowering was maximized at 1,200 mcg of folic acid daily. The results also showed, relative to 1,200 mcg per day, only a small decline in benefit was seen at 800 mcg per day, and no additional benefit occurred with higher doses.¹⁶⁴ One review examined the effects of folic acid on homocysteine levels in patients with various conditions that increase stroke risk. The review included 28 randomized controlled trials, almost half of which included some participants in countries with mandatory folic acid fortification policies. Overall, folic acid use, mainly at doses between 800 and 5,000 mcg daily, with or without other B vitamins, resulted in 15–46% reductions in homocysteine levels. In trials that only included subjects in regions with mandatory fortification, all but one used doses of 2,500−15,000 mcg daily and homocysteine levels decreased 15−30%.¹⁶⁵ A systematic review that included eight studies with a total of 1,140 subjects with mild cognitive impairment living in countries without mandatory folic acid fortification showed folic acid interventions, with or without other B vitamins, decreased homocysteine levels by an average of almost 32%.¹⁶⁶

Folic acid supplementation may enhance cognitive and cardiovascular health while lowering homocysteine levels. One meta-analysis that included findings from 22 randomized controlled trials with a total of 3,604 participants found treatment with folic acid not only lowered homocysteine levels but also improved cognitive function in those with mild cognitive impairment. Moreover, in patients with Alzheimer disease, doses of 3,000 mcg per day or higher had cognitive benefits. Conversely, folic acid was not effective at slowing cognitive loss in those with cognitive dysfunction caused by vascular disease.¹⁶⁷ Another meta-analysis pooled findings from 21 randomized controlled trials with 115,559 participants and found lowering homocysteine levels with folic acid reduced stroke risk by an average of 10%. The benefits were strongest in those who had not previously had a stroke or heart attack, and the efficacy remained consistent regardless of baseline folate levels, folic acid dosage, inclusion of other B vitamins, or degree of homocysteine reduction. A subgroup analysis showed greater efficacy in areas without fortified food or with only partial fortification.¹⁶⁸ A large meta-analysis of 65 randomized controlled trials with 7,887 hypertensive subjects found folic acid plus blood pressure-lowering medication was more effective than medication alone for lowering blood pressure, lowering homocysteine levels, and reducing risk of cardiovascular events and stroke by 13% compared with control groups. The clinical benefits were greatest in those who took folic acid for more than 12 weeks and those whose homocysteine levels dropped by more than 25%.¹⁶⁹

It is important to note that folic acid supplementation can hide or mask a B₁₂ deficiency by preventing or correcting megaloblastic anemia without resolving the neurotoxic effects of B₁₂ deficiency.¹⁶¹ In addition, some evidence suggests the combination of excess folic acid plus B₁₂ deficiency may cause more neurological harm than B₁₂ deficiency alone.¹⁷⁰

Vitamin B12: Cobalamin

Reported dosage: 500–2,000 mcg per day

Vitamin B₁₂, or cobalamin, is found mainly in animal foods, but small amounts are present in mushrooms and fermented foods.¹⁸³ After absorption, B₁₂ is carried in the bloodstream by several different transport proteins, but only holotranscobalamin (holoTC) is biologically active since it can be transported into cells. Once inside the cell, it is used to make adenosylcobalamin, needed for energy production in mitochondria, or interacts with 5-MTHF to become methylcobalamin during homocysteine metabolism.^184,185

The close relationship between vitamin B₁₂ and folate can make it difficult to distinguish their independent deficiencies: B₁₂ deficiency causes a functional folate deficiency by “trapping” folate as 5-MTHF, thereby blocking homocysteine metabolism, because B₁₂is required for the conversion into functional folate; on the other hand, supplementing with functional folate can “mask” a B₁₂ deficiency by normalizing changes to red blood cells that are often an early sign of B₁₂ deficiency.¹⁶¹

Vitamin B₁₂ deficiency is more common in older age. Infants, children, pregnant and lactating women, and people who eat a vegan diet are also at higher risk of deficiency.^161,186 Over the long term, B₁₂ deficiency can lead to a wide range of neurological disorders, including neuropathies, neuromuscular changes, cognitive impairment, depression, and neurodegenerative diseases. Furthermore, by interfering with folate metabolism and the one-carbon cycle, B₁₂ deficiency raises homocysteine levels and risks of related health problems.¹⁸⁷

The most common test for B₁₂ status is total serum B₁₂; however, because only about 6–20% of B₁₂ in the blood is active holoTC, even people with total B₁₂ levels in the normal range may have a functional B₁₂ deficiency. Clinical research suggests serum holoTC levels are a more reliable indicator of B₁₂ status than total B ₁₂ levels, especially in early-stage deficiency.^188,189 Testing both serum total B₁₂ levels and levels of indicators of B₁₂ function such as methylmalonic acid, folate, and homocysteine—all of which increase with B₁₂ deficiency—may also improve detection of deficiency.¹⁸⁴

Supplemental B₁₂, in the form of cyanocobalamin, hydroxocobalamin, or methylcobalamin, is often administered as intramuscular injections due to a long-held perception of poor absorption via the digestive tract; however, evidence now indicates sublingual and oral doses of 500–2,000 mcg per day can effectively raise B₁₂levels without significant difference between the route of administration.¹⁹⁰ In one trial involving patients with pernicious anemia, a condition caused by B₁₂ malabsorption, 1,000 mcg of oral cyanocobalamin daily for one month corrected B₁₂ levels in 23 of the 26 participants.¹⁹¹

Clinical evidence shows supplementing with B₁₂ can safely reduce homocysteine levels. A meta-analysis of 21 clinical trials with a total of 1,625 participants found B₁₂ supplementation lowered homocysteine levels by an average of 4.15 μmol/L and the effect was enhanced when daily doses higher than 500 mcg were used for 12 weeks or longer. The analysis further showed hydroxocobalamin was more effective than other forms of B₁₂.¹⁹² Including B₁₂with other B vitamins in homocysteine-lowering therapy may enhance efficacy.¹⁵⁵ A meta-analysis of trials in elderly subjects with mild cognitive impairment found B12 plus folate lowered homocysteine and improved cognitive function more than either nutrient alone.¹⁵⁴ Furthermore, observational evidence has indicated dietary B12 and folate may work together to reduce all-cause mortality in people with abdominal obesity.¹⁹³

It is important to note that some evidence indicates repeated high doses of cyanocobalamin may be harmful in those with kidney disease; therefore, methylcobalamin or hydroxocobalamin are preferable forms for vitamin B₁₂ therapy.^194-200

Vitamin B6: Pyridoxal 5-Phosphate (P5P), Pyridoxine

Reported dosage: 7.2–50 mg per day, along with other B vitamins

Vitamin B₆ (pyridoxine) is found in a wide array of plant and animal foods.¹⁵⁶ It is a cofactor in more than 150 reactions in cells, including some involved in both folate and homocysteine metabolism.¹⁶⁵ Vitamin B₆ is widely available in foods and severe deficiency is rare; however, low intake and marginal deficiency have been shown to be relatively common around the world, and may be a contributing factor in cardiovascular disease, sarcopenia, frailty, and increased mortality in the elderly.^201-203 Deficiency may be due to medications or conditions that interfere with B₆ absorption or metabolism and is especially prevalent in older individuals.²⁰⁴ Symptoms of deficiency include neurological problems like neuropathy, cognitive dysfunction, and depression, as well as anemia, dermatitis, glossitis (inflamed tongue), and weakened immune function.²⁰⁵

In conditions of adequate methionine availability, conversion of homocysteine to methionine is suppressed, and an alternate metabolic pathway is engaged to regulate homocysteine levels. This other pathway requires B₆ and results in production of cystathionine, followed by cysteine, which can be used to make the powerful antioxidant glutathione.^165,206 Few studies have examined the role of vitamin B₆ on homocysteine-related disorders independently of folate and B₁₂, but a meta-analysis with a total of 369,746 participants determined higher intake of B₆ was correlated with lower risk of coronary heart disease.²⁰⁷ In addition, a large study that followed 2,968 subjects with cardiovascular disease for a median of almost 10 years found lower B₆ levels and higher homocysteine levels were each associated with increased mortality, higher levels of oxidative stress and inflammatory markers, and shorter telomere length for age, suggesting accelerated biological aging.²⁰⁶

At typical doses, pyridoxine is readily transported across cell membranes and converted to the active form of B₆, pyridoxal 5-phosphate (P5P).²⁰⁸ Taking high doses of pyridoxine for prolonged periods results in abnormally high circulating pyridoxine levels. In some people, high intake of pyridoxine may contribute to peripheral neuropathy symptoms such as numbness, tingling, pain, and muscle weakness, mainly affecting the hands and feet. Although the U.S. Food and Nutrition Board recommends a safe upper limit of 100 mg per day, rare cases of pyridoxine-induced peripheral neuropathy have been reported in people taking doses as low as 24–40 mg per day, indicating important differences in individuals’ metabolism of pyridoxine. These effects typically subside following discontinuation.²⁰⁹ Some supplements contain P5P, which raises P5P levels and appears less likely to contribute to nerve problems than pyridoxine.²¹⁰ In addition, supplementing with 50 mg of P5P has been shown to be effective in B-vitamin therapy for high homocysteine levels.²¹¹ Thus, P5P is generally the preferred form of supplemental B6.

Vitamin B2: Riboflavin

Reported dosage: 1.6–8.4 mg per day

Vitamin B₂ (riboflavin) is obtained through dairy foods and whole grains. It is a component of two essential cofactors used by numerous cellular enzymes, including methylenetetrahydrofolate reductase (MTHFR), a critical enzyme in folate and homocysteine metabolism. As a result, B₂ deficiency can trigger functional folate deficiency, especially in carriers of MTHFR mutations associated with reduced activity of the MTHFR enzyme. B₂-containing cofactors are also needed by enzymes that activate vitamins B₁₂ and B₆.^212,213 In fact, blood levels of active B₆ have been found to decrease in proportion to declining B₂ status, independently of B₆ intake.²¹⁴

Vitamin B₂ deficiency is thought to be relatively uncommon in the United States and other regions where white flour is routinely fortified; however, high rates of deficient intake have been reported in other parts of the world.²¹² For example, a study conducted in the United Kingdom, where B₂ fortification is not mandatory, examined B₂ intake in 407 healthy subjects aged 18–92 years old and found 29% were not achieving required intake levels. Furthermore, blood tests showed 37% of participants had a B₂ deficiency which was correlated not only with low intake but also with MTHFR mutations.²¹⁴ High homocysteine levels, high blood pressure, and microcytic anemia with low hemoglobin are among the numerous and wide-ranging signs of B₂ deficiency.²¹²

In a clinical trial involving 35 individuals with specific MTHFR gene mutations, 1.6 mg of vitamin B₂ per day for 12 weeks lowered homocysteine levels significantly more than placebo and the effect was stronger in those with suboptimal B₂ status.²¹⁵ Another trial in 47 MTHFR mutation carriers found 1.6 mg of B₂ per day for 16 weeks promoted conversion of homocysteine into cystathionine via a pathway that requires B₆, but not folate.²¹⁶ A randomized placebo-controlled trial that included 32 healthy Japanese men aged 20–29 years found 800 mcg of folic acid plus 8.4 mg of B₂ daily for two weeks reduced homocysteine levels more than B₂ alone and similarly to folic acid alone. The trial also found combining B₂ and folic acid decreased levels of alanine transferase, a liver enzyme released during liver cell breakdown, while folic acid alone increased alanine transferase levels.²¹⁷

In an observational study involving 20,725 participants in the 2007–2018 National Health and Nutrition Examination Survey (NHANES), higher vitamin B₂ intake was correlated with lower likelihood of having coronary artery disease, and the effect plateaued at 10.5 mg per day.²¹⁸ Another study that analyzed data from 10,480 NHANES (2005–2016) participants found those with the highest folate combined with the lowest B₂ intake had the highest rate of death from cardiovascular disease during an average of 8.5 years of monitoring.²¹⁹ Low B ₂ status has also been correlated with higher risk of cognitive dysfunction in older adults.²²⁰

B Vitamin Combinations

Vitamins B₂, B₆, B₁₂, and folate are inextricably linked through their interdependent roles in homocysteine metabolism and the fueling of methylation pathways.¹⁷⁴ It is becoming increasingly evident that excess availability of individual B-complex vitamins can disturb the balance of interlinked pathways that depend on multiple B vitamins and other nutrients. Despite their interrelatedness, most research has examined the homocysteine-lowering abilities of folic acid alone, with much less emphasis on B₁₂ and B₆ and very little attention to B₂.^155,174

A meta-analysis of 16 randomized controlled trials conducted in countries around the world with varying fortification policies found combined B-vitamin therapy that included folic acid at doses close to 800 mcg daily was more effective for lowering homocysteine levels than single B-vitamin therapy. The analysis also found a combination of 1,000 mcg of folic acid, 20 mcg of vitamin B₁₂, and 7.2 mg of vitamin B₆ was the most effective B-vitamin regimen for lowering homocysteine levels.¹⁵⁵

A randomized controlled trial conducted in China, where folic acid fortification of foods is voluntary, included 100 healthy adult participants with high homocysteine levels; results showed a combination supplement providing 400 mcg of folic acid, 6.4 mcg of B₁₂, 8 mg of B₆, and 1 mg of betaine per day for 12 weeks reduced homocysteine levels by about 3.9 μmol/L more than placebo.²²¹ Other randomized controlled trials have also indicated B vitamin supplementation may benefit populations where food fortification is voluntary. For example, a randomized controlled trial conducted in the United Kingdom included 167 adults aged 50 years and older not consuming B-vitamin supplements or fortified foods greater than four times weekly. After two years, homocysteine levels in those who received a supplement with 200 mcg of folic acid, 10 mcg of B₁₂, and 10 mg of B₆ had decreased by 2.4 μmol/L, or about 17%, more than placebo, and bone mineral density loss had slowed in a subset of participants with low baseline B₁₂ status.²²² In a randomized controlled trial in elderly patients with mild cognitive impairment living in the United Kingdom, supplementing with 800 mcg folic acid, 500 mcg B₁₂, and 20 mg B₆ daily for two years reduced atrophy of gray matter (brain tissue most vulnerable to Alzheimer pathology) up to seven-fold in those with baseline homocysteine levels higher than 11 μmol/L.²²³

One controlled trial showed a combination B vitamin supplement had more benefits than folic acid alone in hypertension patients living in Italy—where there is no folic acid fortification policy. In the trial, 104 subjects with high blood pressure and high homocysteine levels (≥15 μmol/L) received either 5,000 mcg of folic acid per day or a daily supplement providing 400 mcg of folate (as 5-MTHF), 5 mcg of B₁₂, 3 mg of B₆, and 2.4 mg of B₂, as well as 12.5 mg of zinc and 250 mg of betaine. Average homocysteine levels fell from 22.6 to 14.3 µmol/L in the folic acid group and from 21.5 to 10.0 µmol/L in the combination group. Furthermore, 56% of those taking the combination supplement attained homocysteine levels of <10 µmol/L.²²⁴

Diet

A healthy diet that includes an abundance of foods high in B vitamins has been associated with lower homocysteine levels and reduced risk of stroke.^225,226 A Mediterranean diet, which balances high intake of olive oil, fruit, vegetables, whole grains, and plant proteins with modest consumption of dairy products and seafood, has been associated with healthy homocysteine levels.²²⁷ In a study in 237 women, adherence to a Mediterranean diet pattern was more closely correlated with homocysteine levels than either B₁₂ or folate status.²²⁸ Similarly, in a study in 861 70-year-olds in Sweden, adherence to the EAT-Lancet diet, which was designed to support human health and environmental sustainability, was correlated with lower homocysteine levels. The EAT-Lancet diet includes ample whole grains, fruit, vegetables, legumes, nuts, and unsaturated fats, but limits added sugar, dairy, red meat, and other animal food.²²⁹ Eating habits that reflected a Prudent Diet, which includes fruit, vegetables, potato, cassava, cornmeal, fish, and chicken, were also associated with lower homocysteine levels in a study in 281 subjects in Brazil.²³⁰

The issue of plant versus animal protein is complex and likely depends on an individual’s age, digestive capacity, and genetic factors. Animal foods are good sources of B₆, B₁₂, and B₂, and may help vulnerable individuals, including older individuals, meet their nutritional needs. One study in 29 older men with an average age of 74 years and unknown B vitamin status found homocysteine levels dropped more in those who increased their animal protein consumption to boost protein intake to 1.6 grams/kg/day compared with those whose protein intake was maintained at 0.8 grams/kg/day for 10 weeks.²³¹ Nevertheless, in large observational studies, plant protein intake and plant-based diets have been associated with lower homocysteine levels.^232,233 It is noteworthy that vegan diets, which exclude all animal protein, are frequently low in vitamin B₁₂ and have been linked to high homocysteine levels.²³⁴

Observational research provides insights into specific foods that may help keep homocysteine levels from rising. In a study involving 7,521 healthy participants in China, higher fruit intake and better signs of metabolic health were correlated with normal (versus high) homocysteine levels.²³⁴ A study in 227 young Japanese women found higher intakes of fruit and mushrooms, as well as higher soluble, insoluble, and total fiber intake, were each associated with lower homocysteine levels.²³⁵ In a study in 4,175 Ethiopian adults, low fruit and/or vegetable intake was found to be a risk factor for high homocysteine levels.²³⁶ Another study that examined the diets of 252 subjects in Poland with two distinct dietary patterns indicated higher intake of foods such as legumes, whole milk, and whole grains were associated with normal (versus high) homocysteine levels.²³⁷

A study conducted in the Netherlands found high intake of ultra-processed food was associated with higher homocysteine levels.²³⁸ Ultra-processed foods are those formulated, typically using multiple food additives, for features like long shelf-life, palatability, convenience, low cost, and microbiological safety. They are typically calorie-dense but nutrient-poor.²³⁹ In clinical trials in healthy men, consuming the equivalent of two alcoholic drinks per day, in the form of wine or spirits, lowered B vitamin status and raised homocysteine levels, but a similar amount of alcohol as beer, which is a source of B vitamins, did not.^240,241

Being overweight or obese may impair folate metabolism and cause homocysteine accumulation.²⁴² A strong independent link between obesity and high homocysteine levels has been observed.²⁴³ Clinical studies have reported weight loss interventions, both dietary and surgical, increased homocysteine levels in the short term, though some evidence suggests levels may return to baseline in the long term.^244,245

Exercise

Various types of exercise have been found to be associated with lower homocysteine levels. A 2017 analysis from the NHANES found participation in aerobic and strength-training exercise were each correlated with lower homocysteine levels.²⁴⁶ In a large observational study that included 110,551 adults in China aged 40 years and older, exercise was correlated with lower homocysteine levels.²⁴⁷ Another study found that, among older participants, those who were more physically active in general had lower homocysteine levels than those who were less physically active, independent of their B₁₂ and folate status.²⁴⁸ In a study in 497 patients with hypertension, those who reported having a regular aerobic exercise habit had a lower likelihood of high homocysteine levels. In addition, greater intensity, frequency, and total energy expenditure through exercise were each independently linked to lower odds of high homocysteine levels.²⁴⁹

Clinical trials add to the evidence that exercise can reduce homocysteine levels. A randomized controlled trial in 44 women with type 2 diabetes found a 12-week aerobic exercise training program involving three sessions per week of mild- to moderate-intensity exercise lowered homocysteine levels and improved other markers of inflammation and metabolic health. Interestingly, beneficial changes in several biomarkers of metabolic health, including homocysteine levels, were found to be more pronounced in subjects who supplemented with 200 mg of saffron powder along with the exercise intervention.²⁵⁰ Similarly, in a randomized controlled trial in 30 metabolic syndrome patients, an eight-week exercise program that included aerobics and strength training lowered homocysteine levels and improved markers of metabolic and cardiovascular health.²⁵¹

Mind-body exercise has also shown promise as a strategy for lowering homocysteine levels. In a randomized controlled trial involving 170 older adults at high risk of ischemic stroke, a 12-week Tai Chi (a mind-body exercise) program led to multiple benefits including reduced homocysteine levels.²⁵² An observational study that included 326 participants who practiced Tai Chi at least three times per week and 326 matched participants who had no regular exercise habit found the Tai Chi group was nearly four times less likely to have homocysteine levels of 15 μmol/L or higher.²⁵³

Stress Management

The role of stress in cardiovascular disease is well documented; however, its effect on homocysteine metabolism has received little research attention. In one clinical trial, middle-aged and older participants experienced a rise in homocysteine after an experimentally-induced stress, but participants aged 20–30 years old did not.²⁵⁴ Another trial enrolled women with and without menstrual pain in an eight-week yoga intervention. Those with pain had higher baseline homocysteine levels, but both groups had dramatic reductions in homocysteine levels at the end of the yoga intervention: levels dropped by 51% in those with menstrual pain and 46% in those without pain.²⁵⁵

In addition to B-vitamin therapy described in the “How to Lower Homocysteine Levels” section of this Protocol, several nutrients exert a beneficial influence on various aspects of homocysteine metabolism and related pathways.

Betaine

Reported dosage: 1,000–6,000 mg per day

Choline is a nutrient found in many foods, with particularly high amounts in egg yolks, dairy products, fish, beef, chicken, cruciferous vegetables, and soybeans. It is an important structural component of cell membranes, a precursor for the neurotransmitter acetylcholine, and an integral part of brain tissue.²⁵⁶ Choline is also used to make betaine, or trimethylglycine, an important methyl donor that acts as an alternative to folate in metabolizing homocysteine into methionine. Despite its presence in many and various foods, the NHANES found approximately 11% of Americans achieve the recommended intake for choline, which is 550 mg per day for men and 425 mg per day for women.²⁵⁷ In addition to being made in the body from choline, betaine occurs in foods like seafood, wheat germ and bran, beets, and spinach.²⁵⁸

Betaine plays a critical role in regulating homocysteine levels, especially in low folate, low B₁₂, and high methionine conditions.^259,260 Inadequate intake of choline can result in low betaine availability, increased accumulation of homocysteine, and reduced production of SAMe, a critical methyl donor needed for a host of cellular activities.^261,262 Well-regulated homocysteine metabolism depends on a balance between the betaine-dependent and folate-dependent pathways for homocysteine’s conversion to methionine, and deficiencies of either cofactor has been shown to cause depletion of the other.²⁶² Some evidence indicates choline may have a similar relationship with vitamin B₁₂.²⁶³

Betaine supplementation, at doses of 1,000–6,000 mg per day, has been shown to lower blood homocysteine levels and moderate the increase in homocysteine that follows ingestion of methionine.^264-266 A randomized controlled crossover trial in 20 healthy active men found betaine supplementation, at 2,500 mg or 5,000 mg daily for three weeks, lowered homocysteine levels more than placebo.²⁶⁷ In a placebo-controlled trial in 23 athletes, those given 2,500 mg betaine per day during a six-week exercise training program had a lower exercise-induced rise in urinary homocysteine thiolactone, a form of homocysteine known to have toxic effects on blood vessels and interfere with normal protein production and function.^268,269

Choline appears to have a cardioprotective role, which may be related to its homocysteine-lowering effect. In a large observational study that analyzed seven years of data from 14,289 NHANES participants, higher intake of choline was associated with lower risk of cardiovascular disease. The analysis found that every 100 mg increase in choline intake per day was linked to a 9% reduction in cardiovascular disease risk. Furthermore, those with moderate choline intake (those in the third of five intake level categories) had the lowest risk of all-cause mortality. Higher choline intake has also been associated with reduced risk of various cancers.^256,270 Another study examined 11 years of data from 7,341 NHANES participants aged 65 years and older and found choline was one of eight nutrients independently associated with lower likelihood of cardiovascular disease.²⁷¹

It is important to note that excessively high dietary choline intake results in increased trimethylamine N-oxide (TMAO) production by intestinal microbes. TMAO promotes atherosclerosis and increases the risk of major cardiovascular events such as heart attack and stroke. ²⁵⁶

Omega-3 Fatty Acids

Reported dosage: 2,400–3,000 mg per day

Omega-3 fatty acids appear to work synergistically with B vitamins to promote healthy homocysteine metabolism and reduce risks of conditions associated with high homocysteine levels, including cardiovascular and neurological diseases.⁵ Multiple randomized controlled trials have shown that fish oil and its omega-3 polyunsaturated fatty acids (eicosapentaenoic acid [EPA] and docosahexaenoic acid [DHA]) can reduce homocysteine levels, and their effect is augmented by the addition of vitamins B₁₂, B₆, and folic acid.²⁷² In one randomized controlled trial involving 80 subjects with metabolic syndrome, 800 mg of omega-3 fatty acids three times daily for three months not only improved measures of endothelial function but also decreased apolipoprotein B levels and reduced homocysteine levels from an average of 19.3 μmol/L to 13.8 μmol/L.²⁷³ Furthermore, a meta-analysis of findings from 20 randomized controlled trials with a combined total of 2,676 participants found supplementing with omega-3 fatty acids reduced homocysteine levels, and the effects were strongest with daily doses of 3 grams or more for less than 12 weeks and in those with higher baseline homocysteine levels.²⁷⁴

The beneficial effects of omega-3 fatty acids on cardiovascular and neurological health may depend on adequate homocysteine metabolism, which requires healthy B vitamin status. For example, an analysis from one clinical trial in Alzheimer disease patients found treatment with 1,700 mg DHA and 600 mg EPA daily for six months improved cognitive function only in those with homocysteine levels below 11.7 µmol/L.²⁷⁵ Likewise, analysis of data from 782 participants in a randomized placebo-controlled trial found higher omega-3 fatty acid status was correlated with better cognitive performance in subjects with homocysteine levels of 16.8 μmol/L or lower at baseline, and those with high homocysteine levels experienced more cognitive decline than those with low levels during five years of omega-3 fatty acid therapy.²⁷⁶

Healthy omega-3 fatty acid status may also enhance the benefits of B vitamins. In one study, high homocysteine levels were linked to increased brain beta-amyloid (a marker of Alzheimer disease risk) in elderly subjects with low omega-3 status, but not those with high omega-3 status.²⁷⁷ Another study analyzed data from 191 participants aged 65 years or older whose baseline homocysteine levels were 12 μmol/L or higher in a randomized controlled trial and found the positive effects of two years of 400 mcg folic acid and 500 mcg B₁₂ therapy daily on cognitive function were stronger in those with higher DHA levels.²⁷⁸ Clinical trials have also indicated B vitamins’ ability to slow brain tissue atrophy and improve cognitive function in individuals with mild cognitive impairment depends on adequate blood levels of omega-3 fatty acids, especially DHA.^279,280

N-acetylcysteine

Reported dosages: 600–1,800 mg per day

N-acetylcysteine (NAC) is a source of cysteine that can be used in the body to manufacture the important antioxidant compound glutathione. By increasing glutathione production and lowering oxidative stress, it is thought NAC might help mitigate some toxic effects of excess homocysteine. In addition, NAC appears to lower homocysteine levels.^281,282

A meta-analysis of 28 controlled trials found supplementing with NAC not only reduced oxidative stress but also lowered homocysteine levels.²⁸³ In an eight-week, randomized, controlled trial involving 60 participants with high homocysteine levels and coronary artery disease, 600 mg NAC daily was as effective as 5 mg per day of folic acid for reducing homocysteine levels compared with placebo.²⁸⁴ In another trial, 30 patients with high homocysteine levels and Alzheimer disease or a related disorder were treated with a supplement providing undisclosed doses of folate (as 5-MTHF), vitamin B₁₂ (as methylcobalamin), and NAC for periods of time ranging from 2.5 to 34.6 months. Compared to similar patients who received no supplements, brain tissue atrophy in those receiving the B vitamin/NAC combination was substantially reduced. This reduction was proportional to the degree of homocysteine lowering.²⁸⁵ An analysis of data from two placebo-controlled trials in middle-aged men found supplementing with 1,800 mg NAC daily for four weeks decreased homocysteine levels by an average of almost 12%. NAC also lowered blood pressure, particularly in those with high cholesterol and triglyceride levels.²⁸⁶

Taurine

Reported dosages: 0.5–3 grams per day

Taurine is a sulfur-containing non-essential amino acid that is closely related to methionine, cysteine, and homocysteine. Taurine can be made from cysteine or homocysteine in the body and has beneficial effects on vascular, neurological, metabolic, and musculoskeletal health.²⁸⁷ Taurine supplementation has been shown to lower blood pressure and improve cardiac function in heart failure patients.²⁸⁸ It has also been found to improve metabolic health in individuals with metabolic syndrome and those with overweight and obesity.^289,290 Preclinical evidence suggests taurine supplementation may reduce high homocysteine levels and protect heart and blood vessel cells from homocysteine-induced damage.^291-293

In a preliminary trial, 22 middle-aged women (aged 33–54 years) were given 3 grams taurine daily for four weeks. This resulted in a drop in average homocysteine level from 8.5 to 7.6 µmol/L.²⁹⁴ Even in subjects with blood homocysteine levels >125 µmol/L due to a genetic disorder called homocystinuria, taurine supplementation was found to improve vascular function.²⁹⁵

S-adenosylmethionine (SAMe)

Reported dosage: 800–1,600 mg per day

S-adenosylmethionine (SAMe) is a crucial methyl donor in many cell processes, including epigenetic gene modification and neurotransmitter synthesis. Since high homocysteine levels are often the result of poor conversion of homocysteine to methionine, which is a precursor of SAMe, SAMe depletion and homocysteine accumulation usually go hand-in-hand.^8,262 This may be a contributing factor in the relationship between high homocysteine levels and psycho-emotional conditions such as depression, as well as the higher risk of depression seen in carriers of the MTHFR gene variant associated with impaired folate metabolism.^296,297

Clinical evidence suggests SAMe may be helpful in treating depression, including in people with elevated homocysteine levels.^296,298 One case report described the benefit of SAMe in a 32 year old patient with anxiety who was found to have a MTHFR gene mutation: treatment with methylated B₁₂ and folate was not effective for relieving symptoms until SAMe, 400 mg twice daily, was added.²⁹⁹ Although concerns have been raised about the possibility that SAMe supplementation might increase homocysteine production, a trial in subjects with major depressive disorder found that 800–1,600 mg SAMe per day for six weeks did not raise homocysteine levels.³⁰⁰