Flu Season – Fighting Back with Vitamin D

Written by: Dr. Davis Kinney

Based on the number of flu cases we have seen at OneSource over the past couple of weeks, it appears that flu season has arrived. Beyond the flu vaccine most of us feel helpless when it comes to avoiding the flu. While most people think of Vitamin D only in terms of building strong bones, a recent study confirmed what previous studies have suggested; adequate levels of Vitamin D can help protect against the flu virus.

In a study published in the American Journal of Clinical Nutrition in 2010(1), children taking 1,200 IUs of vitamin D3 per day were shown to be 42 percent less likely to contract influenza, compared to children taking a placebo.

Flu “Season” and Vitamin D Levels
Ever wonder why flu tends to be “seasonal” in the fall and winter months, or have you ever pondered why in certain groups like nursing homes some people get the flu and others don’t? The answers may well be related to our Vitamin D levels. (2, 3) Several studies have shown that as the days get shorter and our exposure to sunlight is diminished, our Vitamin D levels also drop. Higher Vitamin D levels appear to have a protective benefit that decreases our susceptibility to the flu virus. In one study of nursing home patients it was found that higher serum Vitamin D levels correlated with a decreased incidence of flu, and conversely, those who did get the flu had the lowest levels of Vitamin D.

What is Your Vitamin D Level?
It is important to know and monitor your Vitamin D level, which can be checked by your OneSource Healthcare provider with a simple blood test. The optimum serum level should ideally be between 50-70 ng/ml year-round. Sun exposure is the preferred method for optimizing vitamin D levels, as your skin also synthesizes vitamin D3 sulfate. However, shorter days and more layers of clothing in the cooler months reduce our exposure to the sun. Not only that, but with increased concerns about sun exposure damaging our skin and increasing the risk of skin cancer, the routine use of sunscreens has widely increased. While this is good for our skin, it may not be so good for our Vitamin D levels. Sunscreens which block UVB rays have been shown to inhibit our natural Vitamin D production as well.

How much Vitamin D?
Vitamin D supplement dosages have recently been revised based on the latest research data. Most adults need about 5,000-8,000 IUs of vitamin D a day to achieve serum levels above 40 ng/ml, which is still just below the minimum recommended serum level of 50 ng/ml. Once the optimal serum level of Vitamin D is obtained the dose may be modified for a maintenance.

The Vitamin D “Hammer”
A great article in the Canadian Family Physician Journal last year introduced the concept of the “Vitamin D Hammer” dose. Gary Swalfenberg, MD recommends a one time 50,000 IU dose of Vitamin D at the first sign of the flu, or 10,000 IU taken three times daily for 48-72 hours or until the symptoms subside.

OneSource Can Help You Fight the Flu
Fight back against the flu this year. If you need a flu shot, we provide them at OneSource with no appointment and no waiting! If you want to know your Vitamin D level, consult your OneSource Healthcare provider – a simple and inexpensive blood test can provide this valuable information.


1. Randomized trial of vitamin D supplementation to prevent seasonal influenza A in schoolchildren. Am J Clin Nutr. 2010 May;91(5):1255-60.
2. Cannell JJ, Vieth R, Umhau JC, Holick MF, Grant WB, Madronich S, et al. Epidemic influenza and vitamin D. Epidemiol Infect. 2006;134(6):1129–40.
3. Schwalfenberg GK, Genuis SJ. Vitamin D supplementation in a nursing home population. Mol Nutr Food Res. 2010;54(8):1072–6.
4. Can Fam Physician. 2015 Jun; 61(6): 507. Gerry Schwalfenberg, MD, CCFP,FCFP

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