A Walk in the Sun

That was the title of a pretty good war movie, but today it’s an encouragement to everyone to take steps to avoid some forms of cancer. Too much sun is associated with an increased risk of non-melanoma skin cancer, but too little sunshine exposure can result in low vitamin D levels, which in turn can increase the risk of 16 sites of cancer (6 gastrointestinal sites, 3 female sites, 3 urogenital sites, 2 upper respiratory tract cancers, and 2 types of lymphomas).

An analysis was done of the mortality rates in the USA for two periods – 1950-1969, and 1970-1994. Adjustments were made for other known cancer risk factors, and then the mortality rates were analyzed in relation to the solar ultraviolet B (solar UVB) irradiation during the two time periods. It was found that the higher the UVB, the lower the cancer rates for the 16 specific sites.

These findings provide support for the theory that solar UVB, by its photosynthetic action in the formation of vitamin D, lowers the cancer risk. There’s now debate as to how to best balance the opposing risks – getting enough vitamin D by sunlight exposure, and covering up fully to avoid skin cancer. The author of the analysis suggests strongly that, until we know more, one should take 1000 to 1500 International Units of vitamin D per day, or expose 10% or 20% of a fair skin for about 20 minutes daily – people with darker skin need 2-4 times longer in the sun to get the same benefit. Only this brief exposure period is necessary; after about 30 minutes the vitamin d synthesis for the day is completed. It just seems to fit in with a short sunbath after lunch . . .