The Deadly Link Between Heart Disease and Alzheimer’sJune 2007
By Edward R. Rosick, DO, MPH, DABHM
If the threat of a heart attack is not enough to compel Americans to trade in their cheeseburgers and recliners for salmon and exercise bikes, how about mounting evidence that cardiovascular disease may greatly increase one’s risk of developing mind-destroying Alzheimer’s disease?
As scientists delve further into the twin pathologies of cardiovascular disease and dementia, they are increasingly convinced that afflictions of the heart and brain share common triggers and biochemical characteristics, including inflammation, oxidative stress, and hypoxia, an oxygen deficit caused by impaired blood flow.
Fortunately, many nutritional and botanical agents that have shown great efficacy in preventing and treating cardiovascular disease also appear to work via several important mechanisms to preserve healthy cognitive function and ward off the crippling effects of Alzheimer’s and other forms of senile dementia.
In this article, we examine the growing evidence indicating that cardiovascular disease may greatly increase one’s likelihood of developing Alzheimer’s, as well as strategies you can adopt today to safeguard the health of your heart and your mind.
Twin Afflictions of Heart Disease and Alzheimer’s
The latest data show that more than 60 million Americans suffer from some form of heart disease, including coronary artery disease, congestive heart failure, and cardiac arrhythmias (abnormal rhythms of the heart). Coronary artery disease in particular affects more than 13 million Americans.1 Although heart disease traditionally has been thought of as a “man’s disease,” nearly half of the 600,000 Americans who will die from heart disease this year are women. With its alarming growth rate and lack of a cure, Alzheimer’s disease is poised to become one of the most insidious medical problems of the twenty-first century. This devastating neurological condition progressively destroys one’s memory and ability to think. Alzheimer’s now affects more than 5 million Americans, including one of eight Americans aged 65 or older and nearly half of those over the age of 85. Someone in the United States develops Alzheimer’s every 72 seconds, and according to current projections, by 2050 a new case of Alzheimer’s disease will emerge every 33 seconds.2-4
Alzheimer’s Destroys Memory in Multiple Ways
While scientists have not yet been able to pinpoint the exact cause of Alzheimer’s, they have been able to elucidate some of the biochemical processes that produce the hallmark mental changes characteristic of the disease. First, Alzheimer’s involves a significant decline in brain levels of acetylcholine, a neurochemical that is vitally important for memory formation and retention. Second, the disease is accompanied by an accumulation of harmful amyloid-beta deposits, or senile plaques, in the brain. Third, brain autopsies of Alzheimer’s patients show evidence of substantial oxidative damage wrought by free radicals. When energy is generated, free radicals are produced in every cell in the body, particularly brain cells; however, in Alzheimer’s disease, free radicals are produced in much greater amounts then normal, leading to significant damage to the brain. In a recent article on this topic in the Annals of the New York Academy of Sciences, the investigators concluded that “altogether, our findings emphasize the importance of . . . oxidative stress in the pathogenesis of [Alzheimer’s disease].” 5
Deadly Connections: Hypoxia, Amyloid-Beta, and Oxidative Stress
While researchers certainly know much more today about how Alzheimer’s affects the brain, we still do not know why this disease afflicts some people and spares others. However, groundbreaking research strongly suggests an intimate link between Alzheimer’s and cardiovascular diseases such as atherosclerosis, hypertension, and stroke.
A recent report in the Proceedings of the New York Academy of Sciences has shown that hypoxia—the reduction in oxygen received by the brain due to decreased blood flow—may be a “trigger” that contributes to the pathogenesis of Alzheimer’s disease.7 The authors of this important research have shown that hypoxia increases the activity of a gene called BACE1, which is involved in the production of damaging amyloid-beta plaques found in the brains of Alzheimer’s patients. The researchers found that hypoxia markedly increased amyloid-beta deposition and plaque formation in central neurons. Since a decrease in the amount of oxygen delivered to the brain may very well set off a cascade of events that culminates in Alzheimer’s disease, conditions like heart disease—a cause of brain hypoxia—provide a stark connection between heart disease and Alzheimer’s.
Besides increasing amyloid-beta production, hypoxic conditions in the brain also heighten levels of oxidative stress, an increase that poses serious dangers for the delicate cells of the central nervous system. Scientists believe that chronic oxidative stress may cause neuronal cell death, which ultimately manifests as the cognitive impairment and brain pathology known as Alzheimer’s disease.8
Finally, hypoxia caused by heart disease may also contribute to the lower levels of acetylcholine observed in Alzheimer’s disease.
Drugs Fail to Correct Hypoxic Damage
Since healthy acetylcholine levels are critically important for memory formation and retention, it is not surprising that most prescription medications currently used to treat Alzheimer’s disease work by increasing this important neurotransmitter. Although they modestly decrease the rate of progression of Alzheimer’s, these medications—known as acetylcholinesterase inhibitors, such as Aricept® (donepezil) and Exelon® (rivastigmine)—do not stop the disease. In addition, these medications can have numerous unpleasant side effects, including nausea, vomiting, diarrhea, and liver damage.10
Another medicine, Namenda® (memantine), targets NMDA (n-methyl-D-aspartate) receptors in the brain, rather than acetylcholine.10 However, like the acetylcholinesterase inhibitors, Namenda® is not a cure, and does nothing to help decrease oxidative stress or the formation of amyloid-beta, two hallmarks of Alzheimer’s disease that are strongly influenced by hypoxia.
With newly emerging evidence showing direct links between cardiovascular disease and Alzheimer’s, it makes perfect sense to use preventive therapies that target both diseases. Although there is currently no approved prescription medication that can accomplish this, a wealth of scientific evidence shows that nutritional and botanical remedies may help prevent and manage both diseases.
Antioxidants Reduce Oxidative Stress
Considerable evidence now shows that antioxidants may help protect against a variety of illnesses, including heart disease, cancer, and neurodegenerative disease.11,12 Since oxidative damage to brain cells is thought to contribute directly to Alzheimer’s disease, it follows that antioxidant supplements may play a vital role in preventing Alzheimer’s disease and other forms of dementia.
For example, a large study of 442 elderly patients in Basel, Switzerland, found a direct correlation between higher blood levels of two common antioxidants (beta-carotene and vitamin C) and memory retention.13 Another study published in 2005, which reported on the risk of Alzheimer’s disease in people who took antioxidant supplements, found that individuals who supplemented with both vitamin E and vitamin C displayed a decreased incidence of Alzheimer’s disease.14
An even more recent study examined the protective action of vitamin E on hypoxia-induced changes in the brains of rats.15 Administering vitamin E prior to experimentally induced hypoxia provided significant brain protection and helped stabilize membrane lipids, an essential component of a healthy brain.
Resveratrol: Benefits for the Brain and Heart
In addition to antioxidants such as beta-carotene, vitamin C, and vitamin E, other nutritional agents with substantial antioxidant properties have shown efficacy against heart disease and Alzheimer’s disease. One of the most intriguing of these is resveratrol. Technically, this compound is a flavonoid polyphenol found in the skin and seeds of grapes, as well as in red wine.
Resveratrol is thought to underlie the “French Paradox,” which refers to the traditionally low levels of heart disease found in France, despite a population renowned for its love of wine and fatty foods. Recent studies have shown that daily consumption of red wine helps offset the deleterious health effects of the French diet and lifestyle, with resveratrol maintaining heart heath by preventing aberrant heart rhythms, increasing levels of beneficial high-density lipoprotein (HDL), inhibiting platelet aggregation, increasing levels of an important vasodilator (nitric oxide), quenching free radicals, and decreasing inflammation.16,17
Recent research has shown that resveratrol not only guards against heart disease, but also may provide important protection against Alzheimer’s. A study in 2003 examined the protective effect of black grape skin extract (which is high in resveratrol) on human endothelial cells that were exposed to oxidative stress similar to that produced by amyloid-beta.18 The grape skin extract protected cells against free-radical-induced damage, leading the researchers to conclude that resveratrol may help protect against amyloid-beta-induced neurotoxicity.
A study published in the journal Gerontology examined resveratrol’s effects on human cells subjected to oxidative stress generated by amyloid-beta.15 Resveratrol was effective in restoring levels of glutathione (an intracellular scavenger of free radicals) in human cells subjected to amyloid-beta. In another recent study, resveratrol helped protect brain cells in the hippocampus (an area of the brain crucial for memory) against hypoxia-induced damage by substantially decreasing hypoxia-induced cell death.16
Yet another intriguing laboratory study showed that administering resveratrol to cells decreased their secretion and intracellular levels of amyloid-beta peptides. Resveratrol did not inhibit the production of amyloid-beta, but instead promoted its intracellular degradation. Although preliminary, these findings suggest a potential role for resveratrol in fighting the accumulation of amyloid-beta plaques in the brains of Alzheimer’s sufferers.21
Ginkgo Provides Multifaceted Neuroprotection
Another supplement that I have recommended to many of my patients as a front-line agent in the fight against Alzheimer’s is Ginkgo biloba. Ginkgo has been used for at least 5,000 years in the management of numerous health concerns, including age-related memory loss.22 Multiple studies have demonstrated that ginkgo extracts can provide remarkable protection against some of the most common pathological changes seen in the brains of Alzheimer’s patients.
As noted earlier, maintaining optimal levels of acetylcholine is one way to fight Alzheimer’s disease. A report published in 2000 showed that standardized ginkgo extract promotes the uptake of the acetylcholine precursor choline in an area of the brain associated with memory function. Furthermore, the ginkgo extract protected the brain against the age-related loss of cholinergic neurons, which communicate using acetylcholine.23 In addition, multiple studies have been shown that ginkgo extracts can protect brain cells against amyloid-beta-induced death.24,25
Ginkgo extracts also confer powerful antioxidant properties. Recent studies have shown that standardized ginkgo extract effectively increased levels of antioxidant enzymes in the hippocampus, the brain’s essential memory center. This likely has the effect of protecting against the free-radical-induced damage that is so prevalent in the brains of Alzheimer’s sufferers.26
Other recent studies have demonstrated ginkgo’s effectiveness in protecting against hypoxia-induced brain damage.27,28 In one study, ginkgo extract protected the brain cells of gerbils against damage from experimentally induced hypoxia.27 This finding led the researchers to conclude that ginkgo extract “is protective against ischemia-induced neuronal death . . . by synergistic mechanisms involving anti-excitotoxicity, inhibition of free-radical generation, scavenging of reactive oxygen species, and regulation of mitochondrial gene expression.”