Retinol, retinol-binding protein 4, abdominal fat mass, peak bone mineral density, and markers of bone metabolism in men: the Northern Osteoporosis and Obesity (NO2) Study.

Context: The association between retinol and bone mineral density (BMD) in males after puberty has not been fully investigated previously.
Objective: To investigate the association between retinol, retinol-binding protein-4 (RBP-4), BMD (g/cm(2)), abdominal fat mass, and markers of bone metabolism in young men.
Design: Longitudinal study.
Participants: Seventy-eight healthy males with a mean age of 22.6+/-0.7 years at baseline. A follow-up was conducted in 73 of the participants 2.0+/-0.4 years later.
Main Outcome Measures: Associations between serum concentrations of retinol and RBP-4, and BMD of the total body, lumbar spine, and hip, serum concentrations of osteocalcin, and carboxy terminal telopeptide of type 1 collagen (CTX), were investigated.
Results: Both retinol and RBP-4 showed an inverse relationship with that of osteocalcin (r=-0.23 to -0.25, P<0.05). Levels of RBP-4 (r=0.26, P=0.02) and osteocalcin (r=-0.23, P=0.04) were also related to abdominal fat mass, and the relationship between RBP-4, retinol, and osteocalcin disappeared after adjusting for this influence of abdominal fat mass. Neither retinol nor RBP-4 concentrations were associated with BMD at any site, CTX as baseline, or changes in BMD during the 2-year follow-up period. Levels of RBP-4 showed a strong association with levels of retinol (r=0.61, P<0.001).
Conclusion: We found a negative association between the bone formation marker osteocalcin with retinol and RBP-4. The association disappeared when adjusting for the influence of abdominal fat mass. Neither retinol nor RBP-4 were associated with peak BMD in young men.