Obesity status influences the relationship among serum osteocalcin, iron stores and insulin sensitivity

Increased iron stores significantly influence the clinical course of several chronic metabolic diseases. Recent studies have shown that iron overload decreases osteocalcin. We aimed to explore the relationship among osteocalcin, iron stores and insulin sensitivity.

Extensive clinical and laboratory measurements, including serum ferritin, cross-linked C-telopeptide of type I collagen (CTX) and osteocalcin (OC) concentrations, were analyzed in 250 adult consecutive Caucasian men. Insulin sensitivity was evaluated through frequently sampled intravenous glucose tolerance tests with minimal model analysis.

Circulating serum ferritin were negatively associated with serum OC and CTX (p = 0.004 and p = 0.045 respectively). In all subjects as a whole, BMI and ferritin contributed to explain 5.2% of OC variance after controlling for age and smoking status. However, the association between OC and insulin sensitivity remained significant only in lean subjects (BMI < 25 kg/m², r = 0.468; p = 0.006) whereas the link between serum ferritin concentration and OC and CTX were significant only in overweight/obese subjects (BMI ≥ 25 kg/m², r = -0.229; p = 0.002 and r = -0.196; p = 0.008, respectively).

The association of circulating osteocalcin with parameters of insulin sensitivity and iron stores were dependent on obesity status. Increased iron stores could contribute to the detrimental metabolic effects of overweight and obesity on bone.