Does the use of sunblock inhibit the skin’s production of vitamin D from sunlight? Is this something we should be concerned about in women with osteoporosis?
—Stephen S. Falkowski, DO, Marlton, N.J.
Consumer and medical publications have provided a great deal of coverage on the vitamin D status of Americans (J Natl Cancer Inst. 2005;97:161-163). Several publications have presented data suggesting that individuals with serum vitamin D levels in the low-to-normal range may actually be vitamin D-deficient (Am J Med. 2004;116:634-639 and JAMA. 2004;291:1999-2006). Other researchers suggest that low-to-normal levels of vitamin D can be attributed to sunscreen use and sun avoidance (J Clin Endocrinol Metab. 1987;64:1165-1168).
Foods containing fish oils are rich in vitamin D, but these are not prominent in the American diet. Thus, for decades, some milk and dairy products in this country have been fortified with vitamin D. The most efficient way to obtain vitamin D, however, is through a complex set of processes that begin with conversion in the skin of 7-dihydroxycholesterol from UV light. The controversy about the impact of sun protection on vitamin D levels has grown because researchers cannot agree on what constitutes “normal” for serum 25-hydroxyvitamin D and similarly cannot agree on the minimum suggested daily intake level of vitamin D. The tanning salon industry has fanned the flames by suggesting that exposure to UV light and tanning is the optimal way to ensure healthy vitamin D metabolism.
Tanning to boost vitamin D absorption is a subject of increasing concern for dermatologists and all clinicians, given the increased risk of skin cancer. We should await solid scientific evidence from our colleagues in endocrinology and bone metabolism to guide us on normal laboratory values and adequate daily intake of vitamin D. Until we have more information, we should continue to encourage appropriate sun protection and suggest that our patients obtain an adequate amount of vitamin D through food sources and supplements. It has been reported that the normal intake for optimal health is approximately 1,000 IU/day for adults. To ensure against toxicity, this should not exceed 2,000 IU daily.
—Jeffrey M. Weinberg, MD (119-3)