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The Vitamin That May Prevent Your Cold and Flu

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Vitamin D is not only the only vitamin that humans can naturally synthesize in adequate amounts, it is also quickly becoming a versatile vitamin. This vitamin can help prevent your cold and flu because it boosts the immune system. In addition, vitamin D has direct antimicrobial actions and it has been shown to improve the efficacy of flu vaccines. This article discusses the various mechanisms by which vitamin D can enhance your natural human response to cold and flu viruses as well as the best form of vitamin D to help you survive this flu season.

Vitamin D and the Immune System

Vitamin D is a rather unique vitamin. It is the only vitamin naturally synthesized by humans in sufficient quantity.

Vitamin D is synthesized in the skin from a metabolite of cholesterol and exposure to certain wavelengths of the ultraviolet (UV) radiation in sunlight.

Even though humans can make vitamin D, vitamin D deficiency is quite common especially during the winter months and in countries found in temperate regions. Low vitamin D levels can be addressed by getting more UV exposure either from sunlight or the special lamps used in tanning.

Alternatively, vitamin D can be derived from foods and supplements. Dietary sources of vitamin D include mushrooms (shiitake and portabella) for vitamin D2 and beef liver, fish liver oil, fatty fish and whole egg for vitamin D3.

The recommended dietary allowance (RDA) for vitamin D increases as we grow older. The RDA for children and adults is 600 – 800 IU per day.

Recently, researchers have found that vitamin D is useful beyond its established role in bone health. One of the exciting new roles of vitamin D involves its effect on the immune system. Studies show that vitamin D promotes innate immunity but not adaptive immunity.

In addition, vitamin D deficiency is strongly associated with viral infections especially the ones that affect the respiratory tract.

The Seasonality of Vitamin D Status and Flu

The first link between vitamin D and respiratory disease was identified as early as 1926 when one health expert found that getting a little sun exposure is associated with higher risks of upper respiratory tract infections.

Since this first association, many researchers have tried to confirm the link between vitamin D and respiratory diseases such as cold and the flu.

While some studies did find that vitamin D deficiency was linked to these conditions, some found that vitamin D supplementation can help prevent and/or treat colds and the flu and others found no association with vitamin D and respiratory diseases.

However, it has been shown that the winter months are associated with both low vitamin D levels and seasonal flu.

It is unlikely to be a coincidence that both vitamin D levels and the flu follow the same seasonal pattern.

Because there are very few sunny days during the winter, most people never get enough sun exposure to synthesize enough vitamin D. Therefore, the winter is the time of the year most associated with low serum vitamin D level because vitamin D synthesis is reduced during this period.

Some experts believe that there are higher incidences of the flu during the winter months because the protection offered by vitamin D is absent.

Studies show that vitamin D can indeed boost the immune system and help the body fight infections better. Therefore, low vitamin D levels may impair the ability of the immune system to keep influenza viruses in check.

However, other factors may also contribute to the occurrence of the flu during the cold winter months. Low humidity can also create an enabling environment for flu viruses to thrive.

Getting Vitamin D

There are a few ways to raise your serum vitamin D levels. The major ones are increased exposure to sunlight, foods that naturally contain vitamin D, foods enriched with vitamin D and vitamin D supplements.

However, the best source of vitamin D is still exposure to the ultraviolet light of sunlight.

Studies that found vitamin D ineffective for preventing and/or treating colds and the flu always use vitamin D supplements at improper doses. Because all vitamin D supplements are not equal, there is no guarantee that oral supplementation with the vitamin will produce optimal serum levels of vitamin D.

In addition, some researchers have shown that the vitamin D produced from exposure to sunlight is a little different and a lot better than the vitamin D delivered by oral supplements.

The skin naturally synthesizes sulfated vitamin D3 while unsulfated vitamin D3 is found in most supplements.

How does vitamin D3 sulfate differ from the unsulfated form of the vitamin? Sulfated vitamin D3 is soluble in water unlike the unsulfated form of vitamin D. This solubility makes all the difference because water-soluble vitamin D3 is more easily transported in the blood while unsulfated vitamin D3 needs to find a carrier protein to bind to before it is carried through the bloodstream.

Because the non-sulfated vitamin D3 found in oral supplements cannot be converted to vitamin D3 sulfate, it can never be as effective as the vitamin D naturally synthesized in the skin.

Studies on Vitamin D, Cold, and the Flu

Vitamin D and Respiratory Tract Infections

A systematic review of past studies published in 2009 in the journal, Endocrine Practice, analyzed studies published between 1948 and 2009 on the effectiveness of vitamin D supplementation in the treatment of infectious disease.

The authors of the review identified 13 well-designed studies. First, the reviewers found that vitamin D supplementation was safe and adverse effects were rare.

Secondly, the reviewers found the strongest support for the efficacy of vitamin D supplementation as an adjunctive option in the treatment of tuberculosis, upper respiratory tract infections (cold, etc.) and flu.

While the researchers called for more studies to confirm the effectiveness of vitamin D, they recommended that doctors should pay more attention to the vitamin D status of patients especially those with respiratory tract infections.

A 2011 study published in The British Journal of Nutrition also found that vitamin D status has a direct and linear relationship with respiratory infections especially seasonal flu.

By measuring serum vitamin D levels in 6,789 participants and correlating these with lung functions, the researchers were able to determine that the prevalence of respiratory infections followed a strong seasonal pattern.

They found that each 10 nmol/l (a tiny value) increase in serum vitamin D level can reduce the risk of respiratory infections by 7%.

In their conclusion, the researchers recommended that the value of vitamin D supplementation for preventing respiratory diseases (cold, flu, etc.) should be explored.

Age, Immune Function and Vitamin D

A 2012 study published in the Journal of Leukocyte Biology investigated the link between vitamin D status, aging, and innate immunity.

The researchers measured serum vitamin D levels in 71 volunteers as well as the levels of circulating cells and cytokines of the innate immune system such as cathelicidins, B cells, T cells, and monocytes.

The results of the study showed that vitamin D levels decreased with age. The participants with the lowest vitamin D levels were also the eldest. In addition, the researchers found that the low vitamin D level associated with aging was also associated with lower levels of circulating cathelicidins.

Lastly, the study found that aging and low vitamin D levels were accompanied by changes in the population and functions of the cells of the innate immune system.

Specifically, the researchers showed that the immune cells affected were mostly the ones needed to mount immune responses against viruses such as the ones responsible for influenza infections.

This study showed that vitamin D production falls as we age and, also supported the need for vitamin D supplementation in the elderly.

In addition, the results also supported the higher RDA for vitamin D recommended for the elderly as well as the increased incidence of severe flu infections among old people. The impaired ability to mount an effective antiviral response can only leave the body open to influenza viruses.

Therefore, vitamin D supplements are important to raise vitamin D status in old age and protect the elderly from seasonal flu.

The Seasonality of Flu and Vitamin D Status

A 2006 paper published in the journal, Epidemiology, and Infection, provided a summary of the link between seasonal flu and seasonal variation in serum vitamin D levels.

The authors first traced the genesis of the idea to R. Edgar Hope-Simpson who proposed in 1981 that epidemic flu followed a seasonal pattern associated with the amount of solar radiation that humans received. They also identified that the reduced production of vitamin D during the winter months may be linked to seasonal flu.

Vitamin D is an immune system modulator that inhibits inflammatory cytokines while putting macrophages in “kill mode”.

While these effects can help prevent/treat cold and flu, vitamin D also promotes the antimicrobial effects of monocytes, neutrophils, natural killer cells. In addition, the authors noted that vitamin D provided protection against lung infections, especially among children.

A 2010 study published in the International Journal of Infectious Diseases also linked sun exposure to vitamin D levels and seasonal flu.

The researchers studied the patterns of pandemic and non-pandemic flu in the USA, Norway, Sweden, Singapore, and Japan and correlated these with seasonal variations of UVB (ultraviolet B light) in those countries.

The results of the study showed that people living in temperate regions barely produced any vitamin D during the winter months. In fact, there was 4 times more UVB radiation during the summer than during the winter.

The researchers found that flu follows a seasonal pattern that coincided with low UVB radiation and low vitamin D status in temperate regions.

A 2010 study published in The American Journal of Clinical Nutrition investigated the usefulness of vitamin D for preventing seasonal flu in school children. The researcher conducted a thorough randomized, placebo-controlled, double-blind study during the winter months of December 2008 and March 2009.

After giving some children 1200 IU per day of vitamin D3 supplements and others a placebo, they tested for influenza A virus through antigen testing and tests of samples obtained by swabbing their nasal passages.

The results of the study showed that vitamin supplementation reduced the incidence of flu by 50%.

The researchers, therefore, concluded that vitamin D3 supplementation can reduce the incidence of seasonal flu.

Vitamin D and the Effectiveness of Flu Vaccines

Flu vaccines are given to prime the immune system and stimulate the appropriate immune response against influenza viruses. Because vitamin D boosts the immune response to viruses, can it improve the effectiveness of flu vaccines?

A 2011 study published in the journal, The Prostate, investigated this theory in a group of prostate cancer patients.

The researchers recruited 35 prostate cancer patients from the Roswell Park Cancer Institute during the 2006 – 2007 flu season. These patients were offered Fluzone, a trivalent flu vaccine. Sera were collected 3 months before and after the vaccination to determine their vitamin D status prior to and at the end of the study.

The researchers found that the patients with the highest serum vitamin D levels were also the ones that showed the biggest serological response to the strains of influenza viruses targeted by the vaccine.

This result showed that vitamin D can boost the immune response triggered by flu vaccines and produce a better antibody response. The result of this immune boost is a significant improvement in the effectiveness of flu vaccines against the viruses targeted.

The JAMA Study

A 2012 study published in The Journal of the American Medical Association received a lot of press because it concluded that vitamin D supplementation offered no benefits in the prevention of cold and flu.

Specifically, the study aimed at determining the effect of vitamin D supplementation on upper respiratory tract infections in healthy adults. To do this, the researchers recruited 322 health adults between February 2010 and November 2011 in Christchurch, New Zealand.

The participants were either placed on placebo or vitamin D supplements. The ones placed on supplements received an initial megadose of 200,000 IU oral vitamin D3 and then the same dose a month later. Subsequently, they were given 100,000 IU of vitamin D3 every month for another 16 months.

The result of this study showed that supplementation with megadoses of vitamin D3 did not reduce the incidence or severity of upper respiratory tract infections.

Flawed Results

This study has been criticized on many fronts but the first criticism to consider is the one provided by the very authors of the study.

The lead researcher agreed that their tests were not perfect or rigorous. He also acknowledged that it was likely that they did not find cold and flu viruses because their samples were wrongly collected and their testing panel was not sensitive enough.

He promised to re-test the samples and look for cold viruses with more sophisticated methods.

Another important flaw identified with this study was the use of megadoses of vitamin D3.

While the researchers argued that they used megadoses of the vitamin to achieve the serum vitamin D levels achieved by past positive studies, it is unlikely that the absorption of vitamin D3 would increase by taking absurdly high doses.

As with the absorption of most nutrients, the body limits the amount of vitamin D absorbed and the rest is simply removed from the gastrointestinal tract.

Therefore, the megadoses of vitamin D3 used in this study should not be expected to perform better than normal doses. So does this mean that normal doses of vitamin D3 are also ineffective against cold and flu? No.

Yet another flaw of this study is the use of monthly doses. There is simply no rationale for giving the participants monthly megadoses instead of daily low doses.

Daily low doses would have produced a steady and sustainable increase in serum vitamin D levels.

The last flaw of this study was the baseline vitamin D status of the participants. A closer examination of the design of the study showed that the placebo group had significantly higher vitamin D levels than the treatment group even at the beginning of the trial.

In fact, 92% of the placebo group already had enough serum vitamin D levels to boost their immune response to cold and flu viruses.

This single observation turns the conclusion of the study on its head. Because the placebo group can derive no more benefits from more vitamin D, they are not the right controls for the treatment group.

In addition, because the participants in the treatment group had lower vitamin D levels than those in the placebo group, they should actually fare worse than the results indicate. It is a good testimony to the immune-boosting power of vitamin D3 supplementation that they fared just as well as the placebo group at the end of the study.

It would seem that this negative study was rigged to find vitamin D supplementation ineffective for preventing cold and flu from the start.

Therefore, no meaningful conclusion can be derived from this study and it does not in any way prove that vitamin D supplementation is useless for preventing cold, seasonal flu or any other form of upper respiratory tract infection.





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