An exploratory Italian study found higher levels of the bone-derived hormone osteocalcin were associated with elevated insulin and estimated insulin resistance despite normal blood sugar, but researchers stress that larger studies are needed.
Researchers in Italy have reported that osteocalcin, a hormone made by bone tissue, may be linked to early metabolic changes in children and adolescents with obesity, even when blood sugar levels are still normal. In an exploratory study published in Nutrients, higher osteocalcin concentrations were associated with higher fasting insulin and greater estimated insulin resistance, suggesting that bone may play a more active role in metabolism than previously thought.
The study, carried out at the Regional Reference Centre for Paediatric Obesity in Messina, reviewed records from 33 children and adolescents aged 5 to 15 with obesity. All had body mass index measurements at or above the 95th percentile for age and sex, and all retained normal glucose tolerance. Yet 22 of the participants met the researchers’ definition of insulin resistance, based on the homeostatic model assessment of insulin resistance and an abnormal insulin response during an oral glucose tolerance test. The group’s average fasting insulin was 25 μU/mL, and mean osteocalcin levels were 112 ng/mL.
Osteocalcin has drawn increasing interest because it is not just a marker of bone formation. Earlier studies have suggested it may influence insulin secretion and sensitivity, and several previous paediatric studies have reached different conclusions. Research involving prepubertal obese children has pointed to a possible role for osteocalcin in energy metabolism, while other work found lower levels in obese children and a negative relationship with insulin resistance. A separate study did not find a significant association at all, underscoring how inconsistent the evidence remains.
The new findings do not prove that osteocalcin causes insulin resistance, or that it is a useful early test on its own. The study was small, retrospective and limited to one centre, which means it could not rule out other influences such as puberty, diet, activity levels or body composition. The authors argue that larger, longer-term studies are needed to determine whether osteocalcin simply reflects early metabolic stress or whether it has a more direct role in the pathway from obesity to later disease.
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