What's the Best Time to Get Sun?

The question: How can you get enough solar exposure to raise your vitamin D levels without unduly increasing your skin cancer risk? Here's a simple (and surprising) piece advice: the best time of day for prudent solar exposure is noon.

Researchers at the Department of Radiation Biology, Institute for Cancer Research, in Montebello, Oslo, Norway, writing in the 2008 issue of Advances in Experimental Medicine and Biology, said that the solar wavelengths that promote malignant melanoma are probably longer (typically morning and afternoon wavelengths) than the wavelengths that generate vitamin D in the body.

Another factor, they said, is that people usually stand in the sun - receiving short, noontime rays at a sharp angle relative to most of the skin. Morning and afternoon sun, conversely, strike skin more directly and penetrate more deeply, meaning the longer spectrum waves have more potential for harm.

So they concluded that brief solar exposures around noon, when wavelengths are shorter and strike at a more indirect angle, should be recommended rather than longer solar exposures in the morning or afternoon.

This remains a controversial question, especially for those who practice "sunbathing," where lying down exposes large areas of skin while the sun is at its peak, but I believe that roughly 10-15 minutes on the face and arms several times a week is safe for most skin types at most latitudes. I will also say that I have advised against midday solar exposure in the past, but this recommendation will make me rethink that advice if these conclusions are replicated by other researchers.

Writing in the August 2008 issue of the American Journal of Clinical Nutrition, Anthony Norman, distinguished professor emeritus of biochemistry and biomedical sciences, says that cells in 36 organs respond biologically to vitamin D.

In addition to its contribution to bone health, it seems to prevent some types of cancer and protect against multiple sclerosis and rheumatoid arthritis. Now, a vitamin D researcher at the University of California, Riverside, has noted that “D” also affects insulin secretion and regulation, heart and blood pressure regulation, muscle strength and brain activity.

He notes that a deficiency of “D” can affect all of those organs including bone marrow, breast, colon, intestine, kidney, lung, prostate, retina, skin, stomach and uterus. Norman recommends an average daily intake of 2,000 IU of vitamin D for all adults, a dosage some other experts have suggested. The current RDA is 200 IU for adults up to the age of 50, 400 IU for those ages 51 to 70 and 600 for those over 70. My current recommendation for supplementation is 1,000 IU.