Sunshine and Vitamin D in the Winter

A friend challenged me recently that he is getting vitamin D in the winter because he gets a sunburn when he skis. So I did some research on vitamin D produced from the sunshine.

It seems there are at least 3 kinds of ultraviolet rays. You can indeed get sunburned from UVA while skiing in the winter...but still not produce any vitamin D. We need UVB to produce vitamin D and that is not strong enough in the winter months to produce the vitamin. Interesting!

“This latter assumption is based on the work of Webb et al. (53) who showed that from November to February there was insufficient solar UVB to synthesize vitamin D3 in Boston.”
http://findarticles.com/p/articles/mi_qa3931/is_200611/ai_n17192606/?tag=content;col1