Can vitamin D supplements reduce my risk of flu during winter?

Leopold D. Galland, MD
Internal Medicine
Not only important for calcium absorption and bone health, vitamin D also stimulates your immune system to produce factors called defensins and cathelicidins that kill viruses.

Most of the vitamin D in our bodies comes from sunlight, so there is marked seasonal variation in vitamin D levels, with higher levels occurring during the summer and lowest levels in winter.

Many researchers have speculated that the increased risk of colds and flu in winter is due to the decline of vitamin D levels that accompanies the decrease in sun exposure.

In one controlled study, use of vitamin D supplementation by postmenopausal women helped to prevent the usual winter increase in cold and flu symptoms. The dose used was 800 or more international units (IUs) a day of vitamin D3. In this study, the protective effect of 2000 IUs/day was greater than the effect of 800 IUs a day.

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Important: This content reflects information from various individuals and organizations and may offer alternative or opposing points of view. It should not be used for medical advice, diagnosis or treatment. As always, you should consult with your healthcare provider about your specific health needs.