Growth Hormone Might Contribute to Weight Woes

Hormonal differences that might help explain why African-American girls grow faster and taller than their Caucasian counterparts could also be stacking the metabolic deck in favor of weight gain in adulthood.

Researchers at the USDA/ARS Children's Nutrition Research Center at Baylor College of Medicine report that African-American girls have higher blood levels of the biologically active form of a potent growth hormone known as "free IGF-1" than their Caucasian peers. The study, the first to report ethnic differences involving Insulin-like Growth Factor-1 (IGF-1), is reported in the September issue of the Journal of Pediatrics.

"This raises the question of whether high levels of free IGF-1 are accelerating growth in African-American children and whether these higher levels could be a factor in excessive weight gain if they persist once growth is complete," says Dr. William Wong, a Baylor professor of pediatrics.

The study involved 136 normal-weight, healthy African-American and Caucasian girls between the ages of 9 and 17. The study was designed to gain insight into the reason African-American girls are more sexually mature, taller and heavier, with both more lean muscle mass and body fat.

"In addition to the higher levels of free IGF-1, the African-American girls had corresponding lower blood levels of two specific binding proteins. These binding proteins tie up free IGF-1 in the bloodstream, making it inactive," he says.

According to Dr. Wong, the liver's production of one of these binding proteins is inhibited by insulin. This is significant because non-diabetic, healthy, normal-weight African-American children also have higher blood insulin levels.

"These results suggest that insulin might be involved in how much free IGF-1 is in circulation," he says.

Higher blood insulin levels are of concern because they might predispose individuals to insulin-resistant type II diabetes. However, even if diabetes does not develop, high insulin levels are thought to contribute to the development of high cholesterol levels, weight problems and hypertension, which are all more prevalent among African Americans.

"If we can unravel the molecular and genetic mechanisms responsible for ethnic differences in free IGF-1 levels, we might also discover factors that predispose African Americans to high insulin levels and related weight and cardiovascular problems," Dr. Wong says.

- JOAN CARTER, R.D./L.D., M.B.A.

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©2006 Texas Medical Center

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