Sources of Vitamin D

With cold and flu season upon us, good nutrition is vital to maintaining a strong immune system. Studies now indicate that vitamin D, once only recognized for supporting bone health, may be a key nutritional component in enhancing immune function.

Here we provide overviews of some of the recent studies touting the immune system benefits of vitamin D:

  • A recent study showed that vitamin D signals the immune system to fight infections. Scientists discovered that T cells—white blood cells that are like soldiers who search out and destroy the targeted invaders—require vitamin D to function. The study author explains, “When a T cell is exposed to a foreign pathogen, it extends a signaling device or ‘antenna’ known as a vitamin D receptor, with which it searches for vitamin D. This means the T cell must have vitamin D or activation of the cell will cease. If the T cells cannot find enough vitamin D in the blood, they won’t even begin to mobilize.” From this study, researchers realize how crucial vitamin D is for activating the immune system. The finding could have significant implications in the fight against global epidemics. Nearly half of the world’s population has sub-optimal levels of vitamin D, a problem that’s getting worse as people spend more time indoors.1
  • Researchers theorized that the flu season occurs in winter months because of the lack of direct sunlight, and subsequent lower levels of protective vitamin D produced in the body. Their research indicates that influenza epidemics, and possibly even the common cold, are brought on by seasonal deficiencies in antimicrobial peptides, resulting from winter-time deficiencies in vitamin D.2
  • In a study of Japanese schoolchildren, vitamin D supplements taken during the winter and early spring helped prevent seasonal flu. The study found that children receiving 1,200 IU of vitamin D daily were 58 percent less likely to catch influenza A.3
  • People with higher blood levels of vitamin D had a 50 percent reduction in the risk of developing acute respiratory tract infections than those with lower blood levels. Additionally, of those with high vitamin D blood levels who did develop infections, there was a marked reduction in the number of days they were ill. Researchers concluded, “Maintenance of a [sufficient] 25-hydroxyvitamin D serum concentration should significantly reduce the incidence of acute viral respiratory tract infections and the burden of illness caused thereby, at least during the fall and winter in temperate zones.”4

1 Von Essen MR, et al. Vitamin D controls T cell antigen receptor signaling and activation of human T cells. Nature Immunology. 2010; 11(4):344-349.
2 Cannell JJ, Vieth R, Umhau JC, et al. Epidemic influenza and vitamin D. Epidemiology and Infection. 2006; 134:1129-1140.
3 Urashima M, et al. Randomized trial of vitamin D supplementation to prevent seasonal influenza A in schoolchildren. American Journal of Clinical Nutrition. 2010; 91(5):1255-60.
4 Sabetta JR, DePetrillo P, Cipriani RJ. Serum 25-Hydroxyvitamin D and the Incidence of Acute Viral Respiratory Tract Infections in Healthy Adults. PLoS One. 2010; 5(6):e11088. 

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