Bone mineral density and its relationship to skin colour in Caucasian females

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Abstract
Low bone mineral density (BMD) is associated with a high risk of osteoporosis and fracture. While women with darker skin, such as women of American African origin, are reputed to have lower risk osteoporosis and fractures compared with women with fair skin such as Caucasian women, with Oriental women having intermediate levels of risk, the reasons for these differences are not clear. We examined the relationship between BMD and skin colour in a population based study of 2005 Caucasian women with a mean age of 58.1 years, resident in Cambridge and categorized into fair, medium and dark complexions by self-report. There was no difference between the three categories of skin colour with regard to body size or life-style characteristics. Women with self-reported fair skin had lowest BMD values, women with self-reported dark skin had highest BMD values, and women with self-reported medium skin colour had intermediate values at all sites. These differences were significant at the trochanter and Ward's triangle of the hip (P values of 0.01 and 0.03, respectively). These associations were independent of age and weight. The associations remained after stratifying for smoking habit and years since menopause. In a cohort of Caucasian women resident at latitude 52 degrees North, fair-skinned women have lower BMD values than darker-skinned women. This association between skin colour and BMD may reflect sunlight exposure times and underlying vitamin D status.