Top Vitamins to Boost Your Immune System – A Closer Look

Dr. Shawn Talbott (Ph.D., CNS, LDN, FACSM, FACN, FAIS) has gone from triathlon struggler to gut-brain guru! With a Ph.D. in Nutritional Biochemistry, he's on a mission to boost everyday human performance through the power of natural solutions and the gut-brain axis.

Supporting your immune system starts with a balanced approach, and vitamins play a key role in this process.

Vitamins like C, A, D, and essential minerals such as zinc and selenium contribute to a strong immune defense by enhancing your body’s ability to fight infections and maintain overall health.

In this post, we’ll explore how these vitamins, especially when combined with immune-boosting foods, boost immune function, the best ways to incorporate them into your diet, and why they are crucial for staying healthy year-round.

Here’s what you’ll find in this post:

The benefits of Vitamin C for immune support

  • How Vitamin A protects against infections
  • The role of zinc and selenium in strengthening the immune system
  • Why Vitamin D is vital for immune modulation
  • How to ensure you’re getting enough of these essential nutrients

The Power of Vitamin C for Immune Function

Vitamin C is the perennial immune-booster and cold-fighter.

Despite the exaggerated old wives’ tale of vitamin C preventing the common cold, it is clear that regular consumption of higher than RDA amounts of vitamin C (500mg to 2 grams daily) can help reduce the duration and severity of colds.

In fact, clinical studies now suggest that about 1 gram of vitamin C consumed on a regular basis throughout the cold and flu season can reduce cold incidence by about 20% and cold duration by almost 40%.

Vitamin C's Role as a Natural Antihistamine

Vitamin C can also act as a natural antihistamine to help open up congested airways.

In some people, however, high doses (500mg or more) can produce mild diarrhea or gas, so you may need to experiment to find the most effective dose for you (reduce intake until symptoms disappear).

Benefits of Combining Vitamin C with Bioflavonoids

Often used in conjunction with vitamin C are a wide variety of bioflavonoids, such as quercetin, rutin, hesperidin, and a number of  catechins and polyphenols found in green tea, grape seed, and pine bark extracts.

All possess powerful antioxidant functions that can both strengthen immune system cells and protect healthy body tissues from damage; some, such as quercetin, may also work as an antihistamine.

Taken separately, or in combination in “mixed bioflavonoid” complexes, these phytochemical compounds can be taken at dosages of several hundred milligrams per day to help prevent infections and alleviate mild symptoms of colds, flu, and allergies such as hay fever.

The Importance of Vitamin A for Immune Defense

Vitamin A is an effective immune system nutrient because it helps keep bacteria and viruses from penetrating the protective mucous membranes (mouth, nose, stomach, lungs) and gaining a foothold in the body.

Safe Dosage for Vitamin A

Since vitamin A is a fat-soluble vitamin, people on low-fat diets may be limiting their consumption of foods rich in vitamin A (liver and dairy) and should consider a supplement.

For men and postmenopausal women, vitamin A is considered relatively safe up to 25,000 IU (7,500 mcg of “retinol equivalents” – or RE) per day, but it is best to avoid dietary supplements with more than 5,000 IU of “pre-formed” vitamin A in favor of supplements that provide at least half of their vitamin A content in the form of natural beta-carotene.

Vitamin A and Pregnancy Considerations

In pregnant women, or in those who could become pregnant, less than 10,000 IU (3,000 mcg RE) per day is more prudent, as high-dose vitamin A is linked to birth defects and other damaging effects in the developing fetus.

All women considering becoming pregnant should discuss vitamin supplementation with a personal physician – especially for vitamin A supplements.

A safer alternative may be to consider a mixed-carotenoid supplement, because beta-carotene can be converted into vitamin A in the body, but only at levels which the body requires.

The Importance of Zinc and Selenium

Selenium is a building block of the body’s key antioxidant enzymes, glutathione peroxidase (GPx). GPx is also thought to play a key role in helping immune system cells protect us from invading viruses and bacteria.

How Selenium Supports Immune Health

Selenium has shown positive results as an important immune system nutrient in studies of cancer (some forms of which may be caused by viruses), AIDS, and chronic fatigue syndrome.

When combined with zinc, these two nutrients provide a boost to general immunity. Since few Americans get the recommended amounts of either selenium or zinc from their diets, a dietary supplement may be needed – especially during the cold and flu season.

To achieve intake levels associated with enhanced immunity, consider a supplement providing selenium (200mcg/day) and zinc (15-30mg/day) together.

Zinc Lozenges for Cold Symptom Relief

Zinc lozenges have become one of the most popular natural approaches to treating the common cold, and there is actually some good scientific evidence to support their use.

Zinc lozenges appear to reduce cold symptoms, such as sore throats, hoarseness, and coughing – and may even be able to shorten the duration of colds by a full day or so.

Like vitamin C, zinc is an essential nutrient for optimal functioning of the immune system; both offer significant antiviral activity when consumed at elevated levels for a short period of time.

It appears, however, that some forms of zinc lozenges may be more effective than other forms, due to the total amount of ionized zinc that the lozenge actually releases into the mouth and throat.

At least one study has shown that lozenges containing zinc gluconate plus citric acid, sorbitol, or mannitol may not deliver high enough levels of ionized zinc; whereas, lozenges which contained glycine (an amino acid) appeared to deliver a higher quantity of ionized zinc.

Vitamin D: The Immune Modulator

Vitamin D is a fat-soluble vitamin that acts as a steroid hormone (the body can make its own vitamin D from cholesterol in the skin after being triggered by the sun’s UVB rays).

Thus, factors such as sun exposure, use of sunscreen, geographic location, gender, age, race, and others will influence a person’s vitamin D status.

Vitamin D's Influence on the Immune System

Vitamin D, as a steroid hormone, influences virtually every tissue system in the body, including our bones, intestines, pancreas, brains, muscles, cardiovascular system, and cell growth cycles (which are related to cancer risk).

In addition to the long list of biological functions of vitamin D listed above, vitamin D also acts as an immune system modulator – preventing excessive expression of inflammatory cytokines and increasing the “oxidative burst” potential of macrophages.

Vitamin D dramatically stimulates the expression of potent anti-microbial peptides which exist in neutrophils, monocytes, and NK cells – as well as in the epithelial lining of the respiratory tract where peptides play a role in protecting the lung from function.

Vitamin D Deficiency and Risk Factors

According to research published in the New England Journal of Medicine (2007), most of us (as many as 1 billion people worldwide) have a vitamin D deficiency.

Some of the most common risk factors for vitamin D deficiency include:

  • Living at Northern latitudes (anywhere above San Francisco or Philadelphia or London – no vitamin D is made in the skin at a latitude of 52-degrees-N from October to March, because the atmospheric ozone filters out the UVB rays of the sun)
  • Failure to get at least 15 minutes of direct sun exposure daily
  • Being dark-skinned or African-American
  • Being elderly (those over 50 make only 25% of the vitamin D of a 20-year-old)
  • Being overweight.

A “normal” range of vitamin D in the blood is 30-74mg/mL – and an “optimal” level suggested by most research is 50-70mg/dL (for protection from heart disease and cancer). 

Being in full sun for 15-30min in the summer will produce approximately 20,000IU of vitamin D, which is released into the circulation within 48 hours (assuming person is light-skinned, non-elderly, and of normal body weight).

Vitamin D's Role in Cancer Prevention

Vitamin D reduces cell proliferation and increases cell differentiations. It also slows the growth of new blood vessels and reduces inflammation – each of which can reduce the risk for certain cancers. In numerous studies, higher intakes of vitamin D and higher vitamin D status have been linked with reduced rates of cancer. 

A study from Creighton University showed a 77% reduction in cancer diagnoses (with 1,100IU/day of vitamin D in postmenopausal women). 

Another, the Health Professionals Follow-up Study (HPFS), showed a reduction by half in colon cancer rates  when comparing the subjects with the highest to the lowest vitamin D concentrations.

Scientific evidence also suggests that vitamin D deficiency is responsible for immune-related conditions including autism and asthma. 

For example, the seasonal vitamin D deficiency that spikes during the winter months (when sun exposure is reduced) has been associated with immune system dysfunction, including autoimmune diseases such as multiple sclerosis (MS), type 1 diabetes, rheumatoid arthritis, and autoimmune thyroid disease. 

Many scientists have even suggested that the vitamin D deficiency in the winter months may be the seasonal trigger for influenza outbreaks around the world.

Seasonal Vitamin D Deficiency and Flu Outbreaks

Flu epidemics rear their heads in the winter (when vitamin D levels are low) and retreat in the summer (when vitamin D levels are higher); this is despite the fact that influenza viruses are found in the population year-round (but epidemics do not “break out” until vitamin D levels fall). 

Vitamin D levels are lowest (in the Northern hemisphere) from November through May (7 months) and highest (enough to prevent flu outbreaks) from June through October (5 months).

Why Vitamin D Supplements Are Needed

Only a very few foods are a good source of vitamin D, including fortified dairy products and breakfast cereals, fatty fish, beef liver (too high in vitamin A for vitamin D to be absorbed), and egg yolks. Cod liver oil is also a good source of vitamin D, but also tends to contain too much vitamin A, which can interfere with the absorption and activity of vitamin D in the body.

Researchers from Creighton University have estimated that 3,000IU/day of vitamin D (total intake including food and supplement sources) is required to assure that 97% of Americans will achieve desired blood levels of 35ng/mL.

The two forms of vitamin D found in dietary supplements are D2 (ergocalciferol) and D3 (cholecalciferol). D3 is the preferred form because it is chemically equal to the form of vitamin D produced by the body, and is 2-3 times more effective than the D2 form at raising blood levels of vitamin D.

A daily dose of 2,000IU of vitamin D3 would be expected to raise blood levels by 20mg/mL – which is about the amount of “deficiency” that the average person might expect to have (especially during the winter months in a Northern-latitude city in the USA).

Conclusion

Maintaining your immune health doesn’t have to be complicated.

By ensuring you get the right amounts of immune-boosting vitamins and minerals, such as Vitamin C, A, D, zinc, and selenium, you can enhance your body’s ability to defend itself against illness.

Incorporating these nutrients into your diet, along with a healthy lifestyle, can make a significant difference in how you feel and how well your immune system performs.

Take steps today to nourish your body and support its natural defenses for a healthier tomorrow.

About the Author

Exercise physiologist (MS, UMass Amherst) and Nutritional Biochemist (PhD, Rutgers) who studies how lifestyle influences our biochemistry, psychology and behavior - which kind of makes me a "Psycho-Nutritionist"?!?!

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