Purpose
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.
Methods
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.
Results
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.
Conclusions
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.