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

Prior nonmelanoma skin cancer is associated with fewer fractures, more vitamin D sufficiency, greater bone mineral density and improved bone microarchitecture in older adults

INTRODUCTION

Prior nonmelanoma skin cancer (NMSC), a biomarker of cumulative lifetime sun exposure, is associated with reduced fracture risk later in life. The mechanism is unknown.

METHODS

Prospective cohort analysis of 1,099 community-dwelling adults aged 50-80 years with baseline and 10 year follow up assessments. Histopathologically-confirmed NMSC diagnosis was established by linkage with the Tasmanian Cancer Registry. Bone mineral density (BMD) and vertebral deformity were quantified by DXA, 25(OH)D by radioimmunoassay, bone microarchitecture by high resolution peripheral quantitative CT, melanin density by spectrophotometry and skin photosensitivity and clinical fracture by questionnaire. 25(OH)D <50 nmol/L was considered deficient.

RESULTS

Participants with a NMSC reported prior to baseline were less likely to sustain an incident vertebral deformity over 10 years (RR=0.74, p=0.036). There were similar reductions for other fracture types but these did not reach significance. Prior NMSC was associated with baseline (RR=1.23, p=0.005) and 10 year longitudinal (RR=5.9, p=0.014) vitamin D sufficiency and greater total body BMD (β=0.021g/cm2, p=0.034), but not falls risk or muscle strength. The relationship between prior NMSC and bone microarchitecture was age dependent (pinteraction<0.05). In the oldest age tertile, prior NMSC was associated with greater volumetric BMD (β=57.8-62.6, p=0.002-0.01) and less porosity (β= -4.6 - -5.2, p=0.002-0.009) at cortical, compact cortical and outer transitional zones.

CONCLUSION

Prior NMSC was associated with fewer incident fractures in community-dwelling older adults. This protective association is most likely mediated by modifiable fracture risk factors associated with an outdoor lifestyle, including 25(OH)D, BMD and bone microarchitecture.

Skin Photosensitivity is Associated with 25-Hydroxyvitamin D and BMD but not Fractures Independent of Melanin Density in Older Caucasian Adults

Whether skin photosensitivity modulates sun exposure behaviours, consequent vitamin D status and skeletal health outcomes independently of constitutive pigmentation have not been systematically investigated. 1072 community-dwelling adults aged 50-80 years had skin photosensitivity quantified by questionnaire and melanin density by spectrophotometry. Bone mineral density (BMD), falls risk and 25-hydroxyvitamin D (25OHD) were measured using DXA, short form physiological profile assessment and radioimmunoassay, respectively. Sun exposure and symptomatic fractures were assessed by questionnaire. Participants were followed up at 2.5 (n = 879), 5 (n = 767) and 10 (n = 571) years. Higher resistance to sunburn and greater ability to tan were associated with reduced sun protection behaviours (RR 0.87, p < 0.001 & RR 0.88, p < 0.001), higher lifetime discretionary sun exposure in summer (RR 1.05, p = 0.001 & RR 1.07, p = 0.001) and winter (RR 1.07, p = 0.001 & RR 1.08, p = 0.02) and fewer lifetime sunburns (RR 0.86, p < 0.001 & RR 0.91, p = 0.001). Higher resistance to sunburn was associated with lower total body (β =  - 0.006, p = 0.047) and femoral neck (β = - 0.006, p = 0.038) BMD, but paradoxically, fewer prevalent fractures (RR 0.94, p = 0.042). Greater ability to tan was associated with higher 25OHD (β = 1.43, p = 0.04), lumbar spine (β = 0.014, p = 0.046) and total body (β = 0.013, p = 0.006) BMD, but not fracture or falls risk. These associations were independent of constitutive melanin density. Cutaneous photosensitivity was associated with sun exposure behaviours, cutaneous sequelae and, consequently, 25OHD and BMD in older Caucasian adults independent of constitutive melanin density. There was no consistent association with fracture outcomes, suggesting environmental factors are at least as important.