Vitamin D

The one health benefit that sunlight has on human skin is the production of vitamin D. Unfortunately, the ultraviolet rays that stimulate vitamin D production (UVB rays) are the same ones that cause sunburn and skin cancer.

There isn't very much vitamin D in the typical American's diet.  Some is present in oily fish (e.g., salmon, mackerel, sardines) milk, and fortified cereal or orange juice, but dietary sources alone are usually not sufficient for a healthy blood level without the addition of substantial sun exposure or a vitamin supplement.

Vitamin D deficiency can cause rickets in children, and osteoporosis in adults.  An increased risk of other ills, such as cancer of the colon, breast, or prostate, as well as multiple sclerosis and type 1 diabetes might be linked to vitamin D deficiency.  More research is needed before all of these associations can be considered certain but in the meantime it seems reasonable for everyone to take prudent measures to maintain an adequate blood level of vitamin D.

During summer months, particularly in the southern latitudes, some individuals acquire enough sun exposure to achieve an adequate vitamin D level.  However, while sun exposure is an effective source of vitamin D, it can simultaneously increase the risk of skin cancer.  When sunscreen is applied to the skin, it not only reduces sun damage, but unfortunately it also blocks vitamin D production. 

Darkly pigmented skin, advanced age, and low UV index (e.g., winter months in northern latitudes) are some of the factors that decrease the amount of vitamin D produced by the skin in response to sun exposure.  Because of the dual impact of the sun's UV rays (skin cancer induction and vitamin D production) those with the lightest skin pigment are at the highest risk of sun damage resulting in skin cancer, while people with darker skin pigment are at lower risk of skin cancer but higher risk for vitamin D deficiency.

Some authorities recommend routine limited or "sensible" sun exposure for vitamin D. However, too many variables affect the amount of exposure time needed (e.g., season, time of day, weather conditions, skin color, age) making it impossible to give a simple recommendation such as "[X] minutes of sun per day" that would be assured to provide sufficient vitamin D for all people. This introduces the risk that people will unintentionally over-expose (fall asleep while sunning) and increase their risk of skin cancer in the process. Sun Safety for Kids agrees with the American Academy of Dermatology which "does not recommend getting vitamin D from sun exposure (natural) or indoor tanning (artificial) because ultraviolet (UV) radiation from the sun and tanning beds can lead to the development of skin cancer1.

The amount of Vitamin D in food or in a supplement is commonly listed in International Units (IU). Evidence is still emerging to determine the ideal safe and effective amount of vitamin D that average healthy people should ingest. At present, the National Institutes of Health2 recommends an intake of 600 IU per day for Americans 1 to 70 years of age.  Some experts recommend a higher intake, in the range of 1,000 - 2,000 IU/day but the NIH warns that intakes in excess of 4,000 IU/day might lead to vitamin D toxicity.  The NIH also discourages intentional sun exposure as a source of vitamin D, saying "it is prudent to limit exposure of skin to sunlight."

Because vitamin D is fat soluble, vitamin D supplements are most effective if taken with food.

The directors of Sun Safety for Kids believe that optimum health will be achieved if people practice careful sun protection year round and compensate by ingesting a sufficient daily amount of vitamin D.

Blood Test

A simple blood test called "25-hydroxy vitamin D" measures circulating vitamin D and provides a fair assessment of the body's vitamin D status. The NIH recommends that the level should be 21 ng/ml or higher, but some experts suggest that blood levels in the range of 30 to 50 ng/ml are preferred. There is no evidence that levels above 50 provide any added benefit and vitamin D toxicity becomes a concern with higher levels.  Levels tend to fluctuate with the seasons (lower in winter/higher in summer) due to incidental sun exposure. A doctor might order the blood test to help in determining the amount of vitamin D supplementation that will provide optimum vitamin D status year round.




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