Age, Body Mass Index, and Lumbar Trabecular Bone Score in Type 2 Diabetes: Gender-specific Associations

Trabecular bone score (TBS) provides information on bone microarchitecture beyond bone mineral density (BMD) and may be particularly relevant in type 2 diabetes mellitus (T2DM). This exploratory cross-sectional study examined associations of age and body mass index (BMI) with lumbar TBS (L1-L4) and their variation by gender in 240 adults with T2DM. Generalized additive models (GAMs) included overall smooths, gender-specific smooths, and tensor-product surfaces. Between-gender smooth contrasts were evaluated using joint simultaneous 95% confidence bands. Supplementary linear-model comparisons assessed fit and repeated five-fold cross-validated prediction errors. Age (edf = 2.767, p < 0.001) and BMI (edf = 2.166, p = 0.001) were associated with TBS in the overall GAM; these tests assessed association rather than departures from linearity. Males had higher TBS than females in the gender-specific smooth model (β = 0.0846, p < 0.001). Direct contrasts supported differences in centered age smooths at approximately 34.0-45.4 and 67.1-74.9 years, but did not identify differences in BMI smooths supported by the simultaneous bands. Gender-specific smooths improved fit over common smooths (p = 0.00133), whereas the additional improvement from tensor-product surfaces did not reach statistical significance (p = 0.08363). GAMs improved in-sample fit but did not consistently reduce cross-validated prediction errors relative to linear alternatives. These findings suggest gender-related variation in the age-TBS association, while evidence for differences in the BMI-TBS association remains insufficient. Residual confounding and the cross-sectional design warrant cautious interpretation and further validation.