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

<strong>Summary:</strong> 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.<p></p> <p><strong>Introduction:</strong> 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.</p> <p><strong>Methods:</strong> 1072 community-dwelling adults aged 50-80 years had constitutive melanin density quantified using spectrophotometry. Participants were followed up at 2.5 (<i>n</i> = 879), 5 (<i>n</i> = 767), and 10 (<i>n</i> = 571) years after the baseline assessment. Prevalence and number of symptomatic fractures were assessed by questionnaire.</p> <p><strong>Results:</strong> Higher melanin density was independently associated with greater prevalence of any fracture (RR 1.08, <i>p</i> = 0.03), vertebral fracture (RR 1.41, <i>p</i> = 0.04) and major fracture (RR 1.12, <i>p</i> = 0.04) and the number of fractures (RR 1.09, <i>p</i> = 0.04) and vertebral fractures (RR 1.47, <i>p</i> = 0.04) in cross-sectional analysis. At the 2.5-year follow-up, higher melanin density was associated with incident fractures (RR 1.42, <i>p</i> = 0.01) and major fractures (RR 1.81, <i>p</i> = 0.01) and the number of incident fractures (RR 1.39, <i>p</i> = 0.02) and major fractures (RR 2.14, <i>p</i> = 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.</p> <p><strong>Conclusions:</strong> 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.</p>