FSH and longitudinal changes in bone marrow adipose tissue composition in older adults

Bone marrow adipose tissue (BMAT) expansion and distinct BMAT composition profiles, including lower unsaturated levels, are cross-sectionally associated with older age. Prospective changes in BMAT composition with aging and the effect of serum follicle stimulating hormone (FSH), which influences both bone and fat metabolism, are unknown. We examined these associations in the AGES-Reykjavik Bone Marrow Adipose cohort, using sex-stratified linear regression models adjusted for covariates including estradiol and testosterone. At baseline, 236 women and 245 men had mean age 81 (SD 4) and 83 (4) years, respectively. Over a mean 3.3 years for 154 women and 2.6 years for 151 men, there was no significant change in total or saturated BMAT. However, mean unsaturated BMAT increased in women (+0.26 %/year, 95 % CI +0.21 %/year to +0.32 %/year) and men (+0.24 %/year, 95 % CI +0.18 %/year to +0.30 %/year). Among women, greater increases in unsaturated BMAT were associated with significantly greater reductions in vertebral trabecular volumetric BMD. At baseline, women in the highest FSH quartile had highest total (66.6 %, 95 % CI 64.3 %-69.0 %) and saturated BMAT (95 % CI 49.3 %, 47.5 %-51.0 %). No relationship existed between FSH and unsaturated BMAT in women or any BMAT outcome in men. Longitudinally, in women, higher FSH was associated with greater increase in unsaturated BMAT. There was no relationship between FSH and change in total or saturated BMAT in women or any change outcome in men. In older adults, total BMAT was stable, but BMAT composition changed with increases in unsaturated BMAT. In women, higher FSH correlated cross-sectionally with higher saturated BMAT but longitudinally with greater gain in unsaturated BMAT. These novel findings warrant further longitudinal studies to better characterize BMAT changes and the role of FSH.