Fibroblast growth factor 21 (FGF21) and bone: is there a relationship in humans?

In animals, high fibroblast growth factor 21 (FGF21) states improve insulin resistance but induce bone loss. Whether FGF21 relates to bone mineral density (BMD) is unknown in humans. Contrary to prediction from animal findings, we found higher FGF21 levels associating with greater BMD in women, independent of age and body composition. Introduction Recent laboratory studies suggest that FGF21 is involved in reciprocal regulation of bone and energy homeostasis. Systemic administration of FGF21 protects animals from obesity and diabetes but causes severe bone loss, smothering the enthusiasm over FGF21 as a potential antiobesity therapeutic. To date, there is no information on whether FGF21 relates to BMD in humans. We thus studied the relationship between plasma FGF21 levels and BMD in healthy adults. Methods Fasting plasma FGF21 levels were measured by enzyme-linked immunosorbent assay and body composition by dual-energy X-ray absorptiometry. Results Among 40 healthy volunteers (age 32 +/- 10 year, 16 women), men had significantly higher lean body mass (p<0.01) and total BMD (p<0.05), and lower percent body fat than women (p<0.01). Median plasma FGF21 levels were not different between the sexes. While therewas no association between FGF21 concentrations and body composition in men, FGF21 levels correlated positively with fat mass (p<0.01) in women. In men, no significant correlation between FGF21 with BMD was observed. However, in women, FGF21 correlated positively with total BMD(R-2=0.69, p=0.003) and spine BMD (R-2=0.76, p=0.001); the correlation remained significant after adjusting for age, ethnicity, and body composition. Conclusions This study reveals for the first time a strong positive association between plasma FGF21 levels and BMD in healthy women, suggesting the association between bone loss and high FGF21 states in animals may not be directly translated to humans in physiologic states. We hypothesize that FGF21 may increase bonemass particularly in women through paracrine mechanisms in the bone-adipose interface.