http://www.oisso.com/2009/08/18/get-your-vitamin-d/

Here’s some interesting info that I found at http://en.wikipedia.org/wiki/Human_skin_color that related to vitamin D.

Dark skin (melanin) protects against ultraviolet light; this light causes mutations in skin cells, which in turn may cause skin cancers. Light-skinned persons have about a tenfold greater risk of dying from skin cancer under equal sunlight exposure. Furthermore, dark skin prevents radiation of UV-A rays from destroying the essential folic acid, derived from B vitamins. Folic acid (or folate) is needed for the synthesis of DNA in dividing cells and folate deficiency in pregnant women are associated with birth defects^[5].

While dark skin better preserves vitamin B, it can also lead to vitamin D deficiency at higher latitudes which in turn can cause fatal cancers affecting the colon, lung and prostate. Dark-skinned people are also at higher risk for rickets, cardiovascular disease, diabetes and multiple sclerosis.^[6] An American study by the USDA found 87% of African Americans to be Vitamin D deficient.^[7] To address this issue, some countries have programs to ensure fortification of milk with vitamin D.

Interesting eh?