Sex- and age-specific effects of fat distribution on bone mineral density.

BACKGROUND: BMI cannot distinguish fat distribution and may mask the true effects of different fat depots on bone mineral density (BMD).To investigate sex- and age-specific associations between fat distribution and BMD and its mediating role in age-related bone loss. MATERIALS AND METHODS: This study analyzed 927 individuals undergoing low-dose chest CT. Visceral (VAT) and subcutaneous adipose tissue (SAT) at L2, VAT/SAT ratio, VAT%, and L1-L2 BMD were quantified. Multivariable regression, restricted cubic splines, and mediation analysis were used to assess sex- and age-stratified associations between fat distribution and BMD. RESULTS: Compared with younger participants, males aged >45 years had higher VAT but lower SAT, whereas females aged >45 had higher VAT and SAT. After adjustment, VAT was inversely associated with BMD across all sex-age groups, with stronger associations in females (β -0.33 vs -0.20 at ≤45 years; -0.27 vs -0.16 at >45 years). SAT was inversely associated with BMD only in females aged ≤45. VAT% was associated with greater odds of low bone mass only in males (OR 1.30, P = 0.03). Exploratory mediation analyses identified significant indirect associations through VAT in males (P < 0.001) and females (P = 0.006), and through the VAT/SAT ratio in males only (P = 0.028). CONCLUSIONS: Higher VAT was associated with lower BMD in females, whereas a higher VAT% was associated with lower BMD primarily in males aged >45 years. These cross-sectional findings highlight sex-specific associations between fat distribution and BMD.