Insulin-like growth factor-1 is associated with bone formation markers, PTH and bone mineral density in healthy premenopausal women

Bone turnover markers (BTM) progressively decrease in young adult women. This might be linked to changes in insulin-like growth factor-1 (IGF-I). Four serum BTMs [serum C-telopeptide of type 1 collagen (CTX), osteocalcin (OC), N-terminal propeptide of type 1 procollagen (P1NP), and bone alkaline phosphatase (bone AP)], serum calcium (sCa), phosphate (sPO₄), magnesium, 25-hydroxyvitamin D [25(OH)D], intact parathyroid hormone (PTH) and IGF-I were measured in 531 young healthy premenopausal women aged 20-50 years participating in the BONTURNO study. In all subjects bone mineral density (BMD) was measured at the spine and at the hip by dual-energy X-ray densitometry. Hip BMD, IGF-I, the four BTMs, sCa and sPO₄ progressively decreased with advancing age and this was associated with proportional increases in PTH. IGF-I levels were significantly and positively correlated with sCa, sPO₄, CTX, OC, P1NP, bone AP, spine BMD, femoral neck BMD and total hip BMD and negatively with age, BMI and serum PTH. When the IGF-I levels were adjusted for age and BMI, the only correlations maintaining a statistical significance were those with serum PTH, P1NP and bone AP. These associations were weak and IGF-I accounted for a only a small proportion of the BTM variance. The mean, age-adjusted IGF-I values were significantly higher in women practicing physical exercises for more then 60 min per week than in sedentary women. In conclusion, in this study we provide evidence of an association between the age-related decline in IGF-I with the progressive decrease in bone formation markers in premenopausal women.