Dark skin protects against melanomas caused by mutations in skin cells induced by ultraviolet rays. Fair-skinned people are ten times more likely to die from melanoma when exposed to similar sun exposure conditions. In addition, dark skin protects against the risk of destruction of vitamin B folate by UV-A radiation. Folate is required for DNA synthesis during cell duplication, and low folate levels during pregnancy are linked to birth defects.
While dark skin protects vitamin B, it can also lead to a deficiency in vitamin D. The benefit of lighter skin is that it blocks sunlight less effectively, and thus aids in the production of vitamin D3, which is necessary for the absorption of the calcium and bone growth. This has led to the introduction of vitamin D fortified milk in some countries. The lighter shades of female skin may be due to the increased need for calcium during pregnancy and breastfeeding.