. . . is vitamin D deficiency the primary cause of winter colds and flu?

Some vitamin D experts believe vitamin D deficiency may be the root cause of winter colds and flu. They point out that we get far less sunlight in the winter (our skin makes vitamin D from UV rays from the sun), and that although vitamin D can be stored in the body for long periods of time, most people don’t make enough during the summer months to last through the winter. The result is that low blood levels of vitamin D are almost universal during the winter months, coinciding with the flu season.

While we need all the vitamins and minerals to build a healthy immune system, and some in particular (vitamins A, C, E, and many of the B vitamins, in addition to zinc and selenium), there is evidence that vitamin D is critical to immune function.

A 2012 study in the Journal of Leukocyte Biology showed that vitamin D levels are lowest in those of us over sixty (the ability to convert the sun’s rays into vitamin D decreases with age) and that innate immune system function declines with age, corresponding to levels of vitamin D. This was true especially for specific components of the immune system that respond to viruses.

Even more telling was a 2010 study from the University of Copenhagen published in Nature Immunology. It found that the immune system’s Natural Killer (NK) cells cannot be activated unless sufficient vitamin D is present. The NKs attack bacteria, viruses and cancer cells.

Whether or not vitamin D is the primary cause of winter colds and flu, it’s just common sense to make sure your vitamin D levels are up to par. Be sure to check your levels by asking your doctor for the 25(OH)D test. Chances are you’ll find you’re on the low side (optimal levels begin at 50 ng/mL). You’ll get 800 IU a day in two tablets of our multi, but for most people this won’t be enough to get your levels up above 50 ng/mL. For extra vitamin D, get our Vitamin D3 Formula, now in gel caps. Our Vitamin D3 is the best form of D on the market – D3 has been shown to be three times more effective than D2, and among the different forms of D3, ours is the most bioactive. Call our office at 1-800-250-3063 with any questions about raising your vitamin D levels.

Alvarez-Rodriguez L. Age and low levels of circulating vitamin D are associated with impaired innate immune function. Journal of Leukocyte Biology. May 2012; 91(5)829-838.

von Essen MR.  Vitamin D controls T cell antigen receptor signaling and activation of human T cells. Nature Immunology. April 2010; 11(4):344-349.

Armas LA.  Vitamin D2 is much less effective than vitamin D3 in humans. Journal of Clinical Endocrinology and Metabolism. November 2004; 89(11):5387-5391.