From Medscape Medical News
Laurie Barclay, MD
August 24, 2010 — Prepubertal overweight children with prediabetes may have lower bone mass and an increased risk for poor skeletal development, according to the results of a study reported online July 16 in the Journal of Bone and Mineral Research.
"Childhood studies of the fat-bone relationship are conflicting, possibly reflecting the influence of metabolic abnormalities in some but not all obese children," write Norman K. Pollock, from Medical College of Georgia's Prevention Institute in Augusta, and colleagues.
The investigators compared bone mass in 41 prepubertal overweight children with prediabetes with that in 99 prepubertal overweight children without prediabetes. The study authors also evaluated associations of bone mass with measures of total and central adiposity, glucose intolerance, insulin sensitivity, lipid profile, markers of systemic inflammation, and osteocalcin. Age range of the children was 7 to 11 years.
Prediabetes was identified from an oral glucose tolerance test, which also allowed measurement of glucose, 2-hour glucose, glucose area under the curve (AUC), insulin, 2-hour insulin, and insulin AUC. Blood levels of lipids, C-reactive protein, and osteocalcin were also measured. Using dual-energy x-ray absorptiometry, the investigators measured total body bone mineral content (BMC), fat-free soft tissue mass (FFST), and fat mass (FM), whereas visceral adipose tissue (VAT) and subcutaneous abdominal adipose tissue (SAAT) were evaluated with magnetic resonance imaging scans.
After adjustment for sex, race, height, and weight, overweight children with prediabetes had a total body BMC 4% lower than those without prediabetes (P = .03). FM correlated directly with BMC in the total sample (β = .16; P = .01), after adjustment for sex, race, height, and FFST.
"This finding provides the first clue linking childhood obesity to skeletal fractures," Dr. Pollock said in a news release. "While overweight children may have more bone mass than normal-weight kids, it may not be big or strong enough to compensate for their larger size."
After controlling for sex, race, height, FFST, FM, and SAAT or VAT, however, VAT (β = -.13; P = .03) and SAAT (β = -0.34; P = .02) were inversely associated with BMC. BMC was not significantly associated with any of the biochemical measurements.
"Taken together, it seems that excessive abdominal fat may play a key role linking pre-diabetes to lower bone mass," Dr. Pollock said. "Our greatest window of opportunity to enhance bone strength and ultimately reduce the risk of osteoporosis is during childhood, before the capacity to build bone diminishes. One of the best things you can do for bone development and general health is exercise."
Limitations of this study include bone measurements derived only from dual-energy x-ray absorptiometry of the total body; and small sample size, precluding separate analysis of data by boys and girls or by white and black race.
"Children have a lot of potential and a whole lot of time to make positive changes," said coauthor Catherine Davis, also from the Prevention Institute. "If you could patent exercise as a drug, somebody would be really, really rich."
J Bone Mineral Res. Published online July 16, 2010. Abstract