Vitamin D is found in our diet, but we also produce it through exposure to sunlight. Research suggests that daily sun exposure without sunblock, particularly between the hours of 10 a.m. and 4 p.m, may support vitamin D synthesis.

A number of regional factors impact the ability for people to get necessary levels of vitamin D through sun exposure alone, including cloud cover patterns, smog, and the angle with which the sun hits the earth. In cities north of 37 degrees latitude (imagine a line drawn between San Francisco and Richmond, VA), it’s hard for people to produce enough vitamin D from sun exposure, especially between the months of November and March. The ability for skin to absorb light also impacts how well people can produce vitamin D, as does the use of sunscreen and the number of hours per day spent inside. It should be noted that UVB rays necessary to produce vitamin D do not penetrate glass, so sitting near a window indoors won’t help you produce sufficient vitamin D.

Because vitamin D is an essential nutrient, it is recommended that individuals with limited sun exposure increase dietary intake of vitamin D either through foods high in vitamin D or through dietary supplementation.

Using a randomized, placebo-controlled, double-blind design, researchers studied the effects of vitamin D supplementation in pregnant women and found that there was an effect on regulatory immunity. IL-10+ CD4+ T cells produce regulatory cytokines which help mediate inflammatory responses. Supplementation of 2,000 IU vitamin D produced a significant increase in the concentration of IL-10+ CD4+ cells in the peripheral blood. Women that took 2,000 IU daily saw an increase of 27% from baseline to their third visit.

Vitamin D3 has been shown to act at the first stage of the body’s immune response. This response has been shown to be very similar to that of IL-10, an anti-inflammatory cytokine which modulates anti-inflammatory responses in the immune system.

Authoritative bodies outside the United States have recognized the relationship vitamin D plays with the immune system. The European Food Safety Authority Panel on Dietetic Products, Nutrition and Allergies (NDA) concluded that a cause and effect relationship has been established between the dietary intake of vitamin D and contribution to the normal function of the immune system and healthy inflammatory response. Additionally, Health Canada corroborates that vitamin D helps to maintain and support immune function.