A new link between skeleton, obesity and insulin resistance: relationships between osteocalcin, leptin and insulin resistance in obese children before and after weight loss.
BACKGROUND
The skeleton is regarded recently as an endocrine organ that affects energy metabolism. However, there are very limited data available concerning the relationships between the osteoblast-derived hormone osteocalcin, weight status, adiponectin and leptin in obese humans, especially in children.


METHODS
We analyzed osteocalcin, adiponectin, leptin and insulin resistance (IR) index homeostasis model assessment (HOMA) in 60 obese and 19 age- and gender-matched normal weight children. Furthermore, these parameters were determined in 60 obese children after participating in an outpatient 1-year lifestyle intervention based on exercise, behavior and nutrition therapy.


RESULTS
Sixty obese children had significantly lower osteocalcin levels (26.8+/-0.8 ng ml(-1)) than 19 normal weight controls (32.2+/-2.3 ng ml(-1)). Boys (29.9+/-1.1 ng ml(-1)) showed significantly (P=0.046) higher osteocalcin levels compared with girls (26.4+/-1.2 ng ml(-1)). In stepwise multiple linear regression analysis adjusted for age, gender and pubertal stage, osteocalcin was significantly negatively related to leptin and HOMA, but not to adiponectin. Changes of osteocalcin in the course of 1 year correlated significantly negatively with changes of IR index HOMA (r=-0.25), standard deviation score-body mass index (SDS-BMI) (r=-0.33) and leptin (r=-0.50). Substantial weight loss in 29 obese children led to a significant increase in osteocalcin and a significant decrease in leptin and HOMA. In 31 obese children without substantial weight loss, osteocalcin levels did not change significantly in the course of 1 year.


CONCLUSIONS
Osteocalcin levels were lower in obese children and were related to IR and leptin both in cross-sectional and longitudinal analyses. Therefore, osteocalcin might be a new promising link between obesity and IR.
Reinehr
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T
Department of Pediatric Nutrition Medicine, Vestische Hospital for Children and Adolescents Datteln, University of Witten/Herdecke, Germany. T.Reinehr@kinderklinik-datteln.de
Roth
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D015415:Biomarkers / Q000097:blood; D015992:Body Mass Index; D001835:Body Weight / Q000235:genetics / Q000502:physiology*; D001842:Bone and Bones / Q000378:metabolism; D002648:Child; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D005858:Germany / Q000453:epidemiology; D006801:Humans; D007333:Insulin Resistance / Q000235:genetics / Q000502:physiology*; D020738:Leptin / Q000097:blood*; D008019:Life Style; D008297:Male; D009765:Obesity / Q000097:blood / Q000235:genetics / Q000503:physiopathology; D015675:Osteocalcin / Q000097:blood*; D011627:Puberty / Q000097:blood; D012044:Regression Analysis; D012737:Sex Factors; D015431:Weight Loss / Q000235:genetics / Q000502:physiology*
D015415:Biomarkers; D020738:Leptin; D015675:Osteocalcin