Prior Nonmelanoma Skin Cancer is Associated with Fewer Fractures, More Vitamin D Sufficiency, Greater Bone Mineral Density, and Improved Bone Microarchitecture in Older Adults

Background: 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 1099 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-hydroxyvitamin D (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 an NMSC reported prior to baseline were less likely to sustain an incident vertebral deformity over 10 years (RR = 0.74, P =.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 =.005) and 10-year longitudinal (RR = 5.9, P =.014) vitamin D sufficiency and greater total body BMD (β = 0.021g/cm², P =.034), but not falls risk or muscle strength. The relationship between prior NMSC and bone microarchitecture was age-dependent (p_interaction < 0.05). In the oldest age tertile, prior NMSC was associated with greater volumetric BMD (β = 57.8-62.6, P =.002-0.01) and less porosity (β = −4.6 to −5.2, P =.002-0.009) at cortical, compact cortical and outer transitional zones. Conclusions: 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.