Cysteine, homocysteine and bone mineral density: a role for body composition?

BACKGROUND Plasma total cysteine (tCys) and homocysteine (tHcy) are associated with body composition, which in turn affects bone mineral density (BMD). OBJECTIVES To investigate whether associations of tCys and tHcy with BMD are mediated through body composition (fat mass and/or lean mass). DESIGN Using data from 5238 Hordaland Homocysteine Study participants, we fit multiple linear regression models and concentration-response curves to explore the relationships between tCys, tHcy, and BMD, with and without adjustment for body mass index (BMI), lean mass and/or fat mass. RESULTS All associations were stronger in women. tCys was positively associated with BMD (women, partial r=0.11; men, partial r=0.07, p<or=0.001 for both), but this association was markedly attenuated after adjustment for fat mass. tHcy showed an inverse association with BMD in women (partial r=-0.09, p<0.001), which remained significant after adjustment for lean mass and fat mass. In men and women, changes in tCys or tHcy during 6 years were not associated with BMD at follow-up. Weight gain during 6 years predicted higher BMD at follow-up (p<or=0.009) independent of nutrient intakes, physical activity and baseline BMI. Baseline tHcy inversely predicted BMD measured 6 years later (partial r=-0.11, p<0.001 in women; partial r=-0.07, p=0.002 in men) independent of baseline BMI, while a positive association of baseline tCys with BMD at follow-up (partial r=0.10 in women, 0.09 in men, p<or=0.001) disappeared after adjustment for baseline BMI. CONCLUSION tHcy is inversely associated with BMD independent of body composition, while the positive association of tCys with BMD appears to be mainly mediated through fat mass.