Sunscreens and Vitamin D - NYTimes.com Q. Will a facial moisturizer with S.P.F. 15 protection keep the skin from generating vitamin D on a sunny day? A. It is possible that the sunscreen will inhibit some of the generation of active vitamin D in the skin, but it is still important to use sunscreen, looking elsewhere for extra D, said Dr. Richard D. Granstein, chairman of dermatology at Weill Cornell Medical College/NewYork-Presbyterian Hospital. "There are studies demonstrating that sunscreens can reduce ultraviolet-radiation-generated vitamin D in the skin," Dr. Granstein said. These are mostly lab studies, he said; other studies examining actual use of sunscreens have failed to confirm an effect, probably because people use too little and fail to reapply the lotions as recommended. In any case, in northern latitudes in winter, it is almost impossible to obtain enough sunlight to generate significant amounts of vitamin D, Dr. Granstein said, and it is possible to supplement vitamin D while avoiding the deleterious effects of sunlight. Ultraviolet radiation is known to be responsible for most skin cancers and is recognized as the most important factor in aging the skin, causing wrinkles and brown spots. "Thus," Dr. Granstein said, "the overwhelming majority of dermatologists recommend that, if one must increase their vitamin D levels, they do so by ingesting foods rich in vitamin D," like fatty fish and fortified foods like milk, or by taking vitamin D supplements.