Do people with darker skin have a greater risk of osteoporosis?

Melanin, the pigment that gives skin its darker colour, absorbs the same UV radiation that the skin needs to produce vitamin D. As a result, people with darker skin produce considerably less vitamin D for the same amount of sun exposure. This is a biologically established mechanism.

That lower level of production has real-world consequences. People with darker skin more often have a vitamin D deficiency, even in countries with abundant sunshine. This has been demonstrated in, among others, Indians, Mexicans and African-American women. In older African-American women, additional exposure to spring sunlight did not produce any measurable improvement in vitamin D levels: in 86% of them, values were deficient despite increased sun exposure.

A vitamin D deficiency is harmful to bones. The deficiency causes parathyroid hormone levels to rise, which promotes bone breakdown and lowers bone density. Severe deficiency can lead to inadequate mineralisation of bone. These are robust findings from multiple studies.

Lower bone density has been measured in Indians than in people of Western European descent. Researchers point to the high prevalence of vitamin D deficiency in that group, with skin pigmentation being a contributing factor alongside limited sun exposure and a diet low in vitamin D. Finally, one Mexican study shows that a specific genetic predisposition combined with darker skin may have an additional effect on vitamin D levels and bone density, but this is preliminary and based on a single study only.

The chain is clear: more pigment reduces vitamin D production, that increases the risk of deficiency, and that deficiency harms the bones. This makes darker skin colour a relevant risk factor for osteoporosis, although age, diet and adequate sun exposure also play a role. If you know that you take in little vitamin D through food and sunlight, it is a good idea to have your levels measured and to discuss supplementation with your general practitioner.