Constitutive melanin density is associated with prevalent and short-term, but not long-term, incident fracture risk in older Caucasian adults.

Abstract

Higher cutaneous melanin reduces vitamin D3 production. This may increase fracture risk. We found that cutaneous melanin density was associated with prevalent and short-term, but not long-term, incident fracture risk in older Caucasian adults. Melanin density either acts as a surrogate marker or its relationship with fracture changes with time. Higher cutaneous melanin reduces vitamin D3 production. This may impact lifetime vitamin D status and increase fracture risk. This study aimed to describe the relationship between spectrophotometrically determined constitutive melanin density, prevalent and incident fractures in a cohort of exclusively older Caucasian adults. 1072 community-dwelling adults aged 50-80 years had constitutive melanin density quantified using spectrophotometry. Participants were followed up at 2.5 (n = 879), 5 (n = 767), and 10 (n = 571) years after the baseline assessment. Prevalence and number of symptomatic fractures were assessed by questionnaire. Higher melanin density was independently associated with greater prevalence of any fracture (RR 1.08, p = 0.03), vertebral fracture (RR 1.41, p = 0.04) and major fracture (RR 1.12, p = 0.04) and the number of fractures (RR 1.09, p = 0.04) and vertebral fractures (RR 1.47, p = 0.04) in cross-sectional analysis. At the 2.5-year follow-up, higher melanin density was associated with incident fractures (RR 1.42, p = 0.01) and major fractures (RR 1.81, p = 0.01) and the number of incident fractures (RR 1.39, p = 0.02) and major fractures (RR 2.14, p = 0.01). The relationship between melanin density and incident fracture attenuated as the duration of follow-up increased and was not significant at the 5- or 10-year follow-up. Constitutive melanin density was associated with prevalent and short-term, but not long-term, incident fracture risk in older Caucasian adults. This suggests melanin density either acts as a surrogate marker for an unmeasured fracture risk factor or the relationship between melanin density and fracture changes with time.