The blood levels of vitamin D in Americans dropped significantly from 1994 to 2004 (Archives of Internal Medicine, March 2009). This is frightening because of the association of low levels of vitamin D and premature death, heart attacks, strokes, and at least 17 different cancers. The authors blame the drop on campaigns aimed at reducing sun exposure because of the fear of developing skin cancer. They also note that people who rely on supplements rather than sunlight are usually deficient because the current recommended doses of vitamin D supplements are way too low (200 IU per day from birth to age 50, 400 international units per day from age 51 to 70 and 600 international units from age 71 and up). It is impossible to meet your needs for vitamin D with foods.

To check for vitamin D deficiency, you need a blood test called D3. If it is below 75 nmol/L, you are deficient and should expose your skin to sunlight or take at least 2000 IU of vitamin D3 twice a day for as long as it takes to raise your blood level of D3 to 75 nmol/L.

Basal cell skin cancers (the most common type) are caused by excessive cumulative exposure to sunlight. Melanoma skin cancers can be caused by a single sunburn. Therefore everyone should go out in the sun, but they should wear hats and use sun screens on the most frequently exposed areas such as the top of the ears, face, and back of the hands. The legs are probably the safest place to expose your skin to sunlight.