Life Extension Magazine®

Flu virus that can kill if immune system is weakened

Winterize Your Immune Defenses

Flu and pneumonia kill 55,000 people a year. Especially vulnerable are those with weakened immune systems such as the elderly. Bolstering immune defenses during winter months is essential for those at risk for infectious illnesses.

Scientifically reviewed by Dr. Gary Gonzalez, MD, in May 2022. Written by: Michael Downey, Health & Wellness Author.

The wintertime virus season makes us all vulnerable to infections.

For some older adults, these infections are life threatening because of immune decline (immune senescence) that occurs with age.

Flu and pneumonia are responsible for 55,000 deaths every year in the US.1 In the presence of immune senescence, flu vaccines may not be sufficient to fight off viral infections.2-4

In this article, we provide a two-pronged strategy to help remain healthy all winter.

The good news is most readers of this publication already follow many of the steps needed to enhance their protective immune function.

Bricks in the Fortress Walls

Natural compounds can help build immune-defenses and protect against wintertime risks such as influenza. While anyone can benefit, it is especially critical for elderly and immune-compromised individuals, since infections can include potentially serious—and even fatal—complications.


healthy lungs  

Cistanche is a type of desert plant whose individual components have been shown to help create more balanced, youthful immune function.

In youth, individuals enjoy abundant naïve T cell populations, which are cells that recognize new threats to the body. These naïve T cells stand ready to destroy new bacteria, viruses, and cancers. Once a naïve T cell performs its job, it then converts to a specialized memory T cell (a cell that can remember a previous threat) that responds only to the same bacteria, virus, etc.

Aging results in an accumulation of senescent T cells that emit inflammatory signals, while depriving the body of vital naïve T cells to fight new invaders and malignancies. This results in a weakening of protective immune function.

Cistanche plant extract stimulates development of naïve T cells and leads to a lower number of memory T cells, which creates a more balanced and healthier immune response. Cistanche also increases natural killer (NK)-cell activity (cells that seek and destroy cells infected with viruses or transformed by cancer)—an action that has been shown in animal research to result in lifespan increase.5

A human study found that individuals taking standardized Cistanche had impressive improvements in their immune profiles after 12 weeks. This included an 11.7% increase in natural killer cell activity and a 20.2% increase in the ratio of CD4 to CD8 cells, which is an indicator of healthier, more youthful immune function.6

Reishi Mushroom

Bioactive components of the Reishi mushroom have been shown to exert biological effects that may help reverse many of the factors of immune senescence. Reishi extracts boost the function of innate immune cells, the immune system’s first line of defense.7,8

It has long been established that Reishi’s unique components (including polysaccharides, triterpenes, and others) enhance crucial immune factors in the body, including hematopoietic (bone marrow derived) stem cells and T cells.9-11

Animal research shows Reishi supports multiple aspects of immune function and longevity.12

But it’s in the realm of viral disease that Reishi mushrooms truly flex their muscles.13 In laboratory cell cultures, Reishi mushrooms stop or slow growth of influenza along with other viruses.13-15

Pu-erh Tea Extract

Studies have shown that the extract of Pu-erh tea—rich in polyphenols and other bioactive molecules, including a unique group of compounds known as theabrownins—may support healthy bone marrow function, which helps rebuild the peripheral immune cellular components.16,17 An animal study demonstrated that Pu-erh tea extract supports immune balance by decreasing the proinflammatory interleukin-6 (IL-6) by a remarkable 43%, while increasing natural killer (NK) cells by 7% and naïve T cells by 10%.16 This results in a positive rebalancing of the immune system, making it more resilient to fight off any type of invader.

Doses of 210 mg/day of Cistanche tubulosa extract, 1,130 mg/day of Reishi mushroom and 650 mg/day of Pu-erh tea extract, when combined, support healthier immune function.

Vitamin C

The activity of many immune cells is closely related to their vitamin C content. This is especially true of the specific cells (phagocytes) that engulf and destroy infecting organisms, and of other cells (T-lymphocytes) that recruit, organize, and direct other immune cells.18 Studies show that immune function can be improved by supplementing with vitamin C.19-21

Vitamin C deficiency has been associated with frequency and duration of colds, along with immune system defects.20

For optimal immune defense, many experts recommend supplementing with 1 gram (1,000 mg) of vitamin C daily in addition to consuming a diet rich in fruits and vegetables.22

Keep in mind that vitamin C at doses between 5,000 mg and 20,000 mg daily (in divided doses to bowel tolerance) can be used when symptoms first appear.

What You Need to Know
Defend Against Wintertime Risks

Defend Against Wintertime Risks

  • Winter means greater vulnerability to infections, especially for aging individuals who face immune senescence.
  • Influenza and pneumonia kill more than 55,000 people in the US every year, and vaccines often confer insufficient protection for aging individuals.
  • The first step is to help protect against infections in the first place by taking a number of prophylactic agents that have been proven to boost the immune system.
  • The second step provides protective agents that can be taken at the very earliest symptoms of an invading infection to provide an instant emergency response.

Vitamin D

Vitamin D wards off the flu by ramping up the body’s innate immune system. This is the branch that responds immediately to dangerous microbes by releasing antimicrobial peptides.23-25 Vitamin D activates the genes that govern antimicrobial peptide production.26 Vitamin D also suppresses inflammatory cytokines, which are particularly dangerous in certain flu cases.23

Compelling evidence supports vitamin D supplementation at much higher levels than are currently recommended by the medical establishment—especially during the winter months when sun exposure is generally inadequate.23

The typical dose range is 5,000 to 8,000 IU of vitamin D3 daily taken with a meal for better absorption.

Annual blood tests can enable one to know if they are taking the proper dose of vitamin D they need to achieve optimal levels of 25-hydroxyvitamin D.

If you do not already maintain a blood level of 25-hydroxyvitamin D over 50 ng/mL, then take up to around 5,000-8,000 IU of vitamin D daily. If you already take around 5,000 IU of vitamin D daily, then you probably do not need to increase your intake.

Throat Probiotic

For those particularly susceptible to throat infections, the novel probiotic S. salivarius K12 produces a powerful, locally-acting class of compounds (lantibiotics), which may reduce throat-infection risk. In a 90-day, controlled clinical trial of volunteers with a history of strep throat or tonsillitis, this potent probiotic reduced the incidence of these infections by 84% compared to the previous year.27

Even during the six-month follow-up period, in which patients did not take the probiotic, they experienced a significant 62% reduction in episodes of strep throat or tonsillitis. This demonstrated that the protection from throat infections continues long after taking the probiotic.27 There were no reported treatment-related side effects or drop-outs reported.27

During winter months, some people dissolve in their mouth one 2-billion CFU (colony forming unit) lozenge daily.

Enzymatically Modified Rice Bran


Aging individuals are more vulnerable to viral (and other) diseases, in part because aging diminishes the functionality of natural killer (NK) cells.28

Scientists have uncovered an enzymatically modified rice bran that has been shown to increase NK-cell activity by up to 84%.29

Enzymatically modified rice bran is produced by exposing crude fiber from rice bran to enzymes isolated from the Japanese culinary mushroom shiitake (Lentinula edodes).30

In a four-month study conducted on individuals who were initially low in NK-cell activity, supplementation with one gram (1,000 mg) of enzymatically modified rice bran per day led to a four-fold increase in NK-cell activity at two months, compared to control responses. And at the end of four months, participants showed a seven-fold increase in NK cell activity.31

Consider adding 500 mg to 1000 mg daily during the wintertime virus season for added protection.


Whey protein has the established capacity to broadly fortify the overall immune system, including modulating the destruction of pathogens and the elimination of toxins.32,33

An array of studies showed whey to be superior to other commercially available protein sources in improving reactivity of the adaptive immune system,34-36 the system that is responsible for building up a pool of antigen-reactive antibodies.32

Mice supplemented with whey produced higher levels of white blood cells, lymphocytes, and cytokines—resulting in greater immune responsiveness and reduced infection severity.37

Adding one or two scoops daily of whey protein to a regimen provides biological components that have beneficial impacts on the immune system.


A component of mother’s milk, lactoferrin has well-documented immune-potentiating effects.38-40

Research shows that lactoferrin may stimulate macrophages,41 which in turn may help to induce cell-mediated immunity. Although many of these studies are on animals, lactoferrin is naturally present in humans, suggesting an innate human antimicrobial function.42,43

A study showed that lactoferrin inhibits viral infection by interfering with the ability of certain viruses to bind to cell receptor sites.39

A dose of 300-1,200 mg daily is suggested to provide yet another layer of protection during the wintertime virus season.

The Emergency Response Team

Prevention is always preferable. But if a microbe slips through the defenses, it is important to respond aggressively the instant that any symptoms of a cold or flu first appear. Doing so will help to stop the microbe dead in its tracks before it has a chance to gain a foothold—and will help ensure optimum health throughout the winter.

The following six components make an especially effective “emergency response protocol” and increase the body’s ability to fend off and avoid infection.


You may be familiar with cimetidine (brand name, Tagamet®) as a drug sold over the counter in pharmacies to combat heartburn. But cimetidine has the unexpected beneficial side effect of boosting immune function. It does this by reducing the activity of T-suppressor cells, an action that prevents the immune system from prematurely shutting down a needed immune response.44 In this way, cimetidine can be particularly effective in blocking and killing viruses. Cimetidine also has other immune-modulating effects, such as increasing NK-cell activity and boosting levels of the immune stimulants interleukin-2 and gamma interferon.45

Although taking cimetidine is a powerful way to temporarily turn up the immune system, it is not intended for extended use. When an emergency immune response is needed, take 800 mg daily for 3-5 days to boost immunity during this critical window, and then discontinue its use.

Cimetidine also has powerful interactions with certain other medications. Before taking cimetidine, read the package insert in case this drug is contraindicated with your current prescriptions. For a list of known interactions, please refer to the box on cimetidine risks accompanying this article.

Cimetidine: Potentially Serious Interactions with Other Medications

Cimetidine can cause increases in plasma concentrations of certain other drugs. Some of the drugs with which cimetidine can negatively interact include:

  • Warfarin (Coumadin®), an anticoagulant,
  • Sildenafil (Viagra®), a PDE5 inhibitor for erectile dysfunction,
  • Phenytoin (Dilantin®), an anticonvulsant,
  • Propranolol (Inderal®), a beta-blocker used to reduce blood pressure and heart rate,
  • Nifedipine (Procardia®), a Ca2+-channel blocker primarily used to lower blood pressure,
  • Diazepam (Valium®), an antianxiety medication, and
  • Several tricyclic antidepressant drugs, lidocaine, theophylline (anti-asthmatic), and metronidazole (an antifungal).

In patients with poor liver or kidney function, and in elderly patients at risk for neuropsychiatric illness, cimetidine dosage should be reduced to 300 mg every 12 hours. Further reduction may be necessary depending upon patient tolerability.

Close monitoring of prothrombin time (PT) is recommended with the anticoagulant warfarin (Coumadin®), and careful adjustment of the anticoagulant dose may be necessary with cimetidine treatment.

Aging men with pre-existing erectile dysfunction who are using sildenafil (Viagra®) should be aware that cimetidine boosts drug exposure by almost 60%. Because of that, these men should strongly consider using a reduced dose of sildenafil (Viagra®) if also using cimetidine.

For all individuals who wish to add cimetidine to their winter-proofing protocol, this drug should only be taken for 3-5 days at the first onset of early flu-like symptoms.

Under no circumstances should cimetidine be taken for longer than 60 days.

High-Allicin Garlic

High-allicin garlic has shown strong antiviral effects and support for healthy immune function.46,47 When symptoms first appear, take 9,000 mg of high-allicin garlic once or twice a day. Be sure to take it before meals, as taking such high amounts of this highly potent form of garlic will cause painful stomach-esophageal burning if it isn’t followed immediately by food.

Don’t worry if it causes you to have a strong sulfur odor. Saturating the body with this pungent garlic is the antiviral objective.

Aged Garlic Extract

Aged garlic has unique, immune-boosting compounds that work differently than those found in high-allicin garlic.48 For a more complete emergency response to wintertime symptoms, add 3,600 mg of aged garlic extract to the protocol at the first sign of a cold.


Dehydroepiandrosterone (DHEA) and its metabolites have demonstrated powerful immune-enhancing and antiviral effects.49 As soon as flu-like symptoms appear, take 25-100 mg of DHEA early in the day. DHEA helps mount an immune response while also protecting against dangerous inflammatory cytokine responses that sometimes occur in response to viral infections.

Zinc Lozenges

Rhinoviruses—some of the viruses that cause the common cold—attach to cell receptor sites in sinus and throat tissues and then replicate out of control.50 Zinc acetate lozenges can be effective in warding off the common cold because it binds to those same cell receptor sites, helping prevent rhinoviruses from taking hold.

At the first hint of a cold symptom, completely dissolve one 18.75 mg lozenge of zinc acetate every two waking hours. Do not exceed 8 lozenges daily, and do not use for more than three consecutive days. Fortunately, that should be all the time needed to block an invading cold bug from latching onto cells in your nose and throat.

It is critical to initiate zinc lozenges at the very first symptom of a common cold. Even if you are not sure a cold is manifesting, suck on at least one zinc acetate lozenge to ensure you are availing yourself of this protective effect. If you wait more than 24-48 hours after a cold manifests, zinc lozenges are of little value.

High-Dose Melatonin

Melatonin delivers broad-spectrum immune-enhancing effects and fights viral diseases.51

At the first sign of flu symptoms, start taking 3 mg-40 mg of melatonin at bedtime. This will induce a powerful immune response, while also promoting the deep sleep needed to support the immune system’s ability to fend off infection.52,53



Wintertime is virus season. For older adults, these infections can be potentially life-threatening.

Between them, flu viruses and bacterial pneumonia kill 55,000 Americans annually, and vaccines provide inadequate defense for many elderly individuals.

This article has laid out a two-pronged strategy for remaining healthy all winter and avoiding further weakening the immune system.

The first phase of this strategy provides an array of prophylactics that serves as a fortress against infection.

For prevention, not every one of these nutrients needs to be taken. Cistanche, Reishi, and Pu-erh tea may be all most people need to bolster their immune defenses. They also cost relatively little.

The throat probiotic may only be needed to be taken 90-days each year to gain protective benefits. It is good to keep on hand in case a sore throat manifests. This is also a low-cost item.

Lactoferrin, whey, and enzymatically modified rice bran have some overlapping immune benefits. They are more expensive than Cistanche, Reishi, and Pu-erh tea combination supplements. (Cistanche provides some similar benefits to lactoferrin-whey-rice bran.)

Most readers of this magazine already take sufficient vitamin C, DHEA, and vitamin D.

The second phase provides a team of emergency responders to be taken at the very earliest sign of symptoms to kill off infections before they become chronic.

Employing this two-pronged strategy can help protect your body against winter’s annoying—and even potentially deadly—infectious risks.

If you have any questions on the scientific content of this article, please call a Life Extension® Wellness Specialist at 1-866-864-3027.


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