skip to Main Content

Why You Need to Maintain Vitamin D Levels During Cold and Flu Season

By Tom Nikkola, CSCS, CISSN, Pn1

If you live in the northern latitudes, you’re in the midst of flu season. Signs for flus shots seem to be everywhere, even though the flu shot seems to be ineffective for more than ¾ of those who get the shot.

Some experts believe there is a simpler solution to reducing the risk of getting the flu: Vitamin D.

Vitamin D may be the most-talked-about micronutrient in recent history. Studies continue to show numerous benefits of maintaining optimal vitamin D levels. Since the average person spends very little time outdoors in the sun, it’s nearly impossible to maintain optimal vitamin D levels through lifestyle and diet. Even foods fortified in vitamin D contain a fraction of what most people require to maintain optimal levels.

Over the past few years, scientists have begun to realize that vitamin D deficiency can make the body more vulnerable to flu infections.[i]

Unfortunately, there haven’t been many clinical trials performed to prove vitamin D can reduce the occurrence of flu. Large, placebo-controlled, double-blind studies are very expensive and are generally funded by pharmaceutical companies. Since vitamin D is such an inexpensive supplement, even from top-quality manufacturers like Thorne Research, it’s unlikely these kinds of trials would be performed. There wouldn’t be any profit made from running these studies.

However, there was a recent study done on children in Japan recently that does provide some strong evidence for vitamin D’s role in flu reduction. In this particular study, Japanese children were given 1200 IU of vitamin D3 or a placebo from December 2008 through March 2009.

At the end of the study, 18.6% of those who were using the placebo had gotten the flu, while only 10.8% of those who received the vitamin D got the flu.

A 42% reduction in the occurrence of flu is significant, especially considering the fact that children’s vitamin D levels were not checked. It’s possible the occurrence of the flu could have been reduced even more if the study would have been designed using enough vitamin D to achieve optimal blood levels in the children.[ii]

Nevertheless, the results from the study were impressive, especially considering there is not a significant amount of research on the flu vaccine’s ability to reduce the occurrence of the flu.

Beyond the Flu

Vitamin D impacts the functioning of over 200 genes in the body. Deficiencies have been linked to autoimmune disease, rheumatoid arthritis, type I diabetes, some cancers and dementia.[iii]

Low vitamin D levels have also been connected to metabolic syndrome,[iv] poor blood-glucose control[v] and asthma.[vi] Another study recently showed that higher vitamin D levels supported greater weight loss.[vii]

Deficiencies in D

More than half of the world’s population is deficient in vitamin D, with even more having levels below optimal ranges.[viii] In the United States, as much as 70-80% of the population may be deficient.[ix]

Pregnant women are equally as likely to be deficient in vitamin D.[x]

The average person’s vitamin D level is only 16-25 ng/mL, well below the 45 ng/mL considered to be the lower end of optimal. To raise blood levels appropriately, it’s estimated an extra 3000-4000 IU/day is necessary for supplementing.[xi]

Testing For and Increasing Vitamin D

With the extremely high prevalence of vitamin D deficiencies, it’s surprising physicians don’t demand more frequent vitamin D testing for their patients. Ideally, it should be done twice per year. If you get lab testing done more often for other reasons, it doesn’t hurt to include a check of vitamin D more often. It’s pretty inexpensive.

Fortunately, you can order the test through your local Life Time Fitness center or through the Life Time online store.

Sunlight is the most powerful source of vitamin D, but it requires baring most of your skin during peak hours of the day. You also need to get pretty direct light, so even if you had the ability to lay on your deck in January in the middle of the day in Minnesota, it’s still not enough direct sunlight to affect vitamin D levels much.

In addition, as we age, our ability to convert the sun’s rays on our skin to vitamin D diminishes. Food sources are generally low in vitamin D, so most people will find it necessary to use supplemental vitamin D.


Getting a shot or using a drug often seems like an easy fix to avoiding sickness and promoting health. However, the nutrients we get from food and natural lifestyles often help us prevent many of the diseases we’re faced with in modern times.

Looking at the long list of issues related to vitamin D deficiency, and considering how easy it is to measure vitamin D, there’s no reason people should be deficient. Take the time and spend the money to check your vitamin D levels. It’s more than just the flu you may be able to avoid.

Thanks for reading. If you learned something new and thought this was valuable, please share it.

[i] Raloff J. Vitamin D is a flu fighter. ScienceNews. March 16, 2010

[ii] Urashima M, Takaaki S, Okazaki M, Kurihara M, Wada Y, Ida H. Randomized trial of vitamin D supplementation to prevent seasonal influenza A in school children. Am J Clin Nutr. 2010;91:1255-1260

[iii] Wellcome Trust. Vitamin D Found to Influence Over 200 Genes, Highlighting Links to Disease. ScienceDaily 24 August 2010.

[iv] Daniells S. Low vitamin D linked to metabolic syndrome in seniors. Nutraingredients. July 2, 2010

[v] Doheny K. Low Vitamin D Linked to Poor Diabetes Control. WebMD. July 21, 2010 (

[vi] Laino C. Low Vitamin D Levels Linked to Asthma. WebMD. March 3, 2010

[vii] Shahar D, Schwarzfuch D, Fraser D, et al. Dairy calcium intake, serum vitamin D, and successful weight loss. Am J Clin Nutr. September 1, 2010, published ahead of print

[viii] Medical News Today. Vitamin D Expert Says More Than Half The World’s Population Gets Insufficient Vitamin D. Medical News Today online article. July 19, 2010. (

[ix] Hyman M. Vitamin D: Why You Are Probably NOT Getting Enough and How That Makes You Sick. The Huffington Post. May 22, 2010

[x] McGreevey S. More Pregnant Women Not Getting Enough Vitamin D. Medical News Today. May 12, 2010

[xi] Grant W. In defense of the sun: An estimate of changes in mortality rates in the United States if mean serum 25-hydroxyvitamin D levels were raised to 45 ng/mL by solar ultraviolet-B irradiance. Dermato Endocrinology. 2009;1(4):207-214

The posts on this blog are not intended to suggest or recommend the diagnosis, treatment, cure, or prevention of any disease, nor to substitute for medical treatment, nor to be an alternative to medical advice. The use of the suggestions and recommendations on this blog post is at the choice and risk of the reader.
Back To Top