Bone mineral content continues to increase in obese adolescents during weight loss

Obese teenagers who succeeded in losing weight in a year-long medically supervised weight control program also saw their bone mineral content increase over that period, say researchers from The Children's Hospital of Philadelphia.

The finding was reassuring, because adolescence is a critical period for bone health in later life.

A study in the current issue of the journal Obesity studied 62 adolescents between the ages of nine and 17 years who participated in a trial looking at the effectiveness of a comprehensive, family-based, behavioral weight control program in conjunction with a weight loss drug, sibutramine. The researchers previously reported the combination of behavioral changes and medication helped very obese teenagers lose weight.

In adults, obesity is associated with increased bone mineral density and voluntary weight loss is associated with a decrease in bone mineral density. The findings in this study show that bone mineral content continues to increase in this adolescent population despite weight loss.

“The growing pediatric obesity epidemic raises important clinical and public health questions about the effects on lifelong bone health of early onset obesity and its treatment,” said Nicolas Stettler, M.D., M.S.C.E., pediatric nutrition specialist at The Children's Hospital of Philadelphia and lead author of this study. “Although fractures due to low bone mineral content are mainly a problem for the elderly, the amount of bone mass acquired during puberty is the key determinant of lifetime fracture risk.”

Using a dual energy X-ray absorptiometry scanner (DXA), researchers looked at specific body areas including legs, arms and lumbar spine as well as the bone mineral content of the whole body. The data was compared with a reference group of 66 adolescents. Bone mineral content of the obese subjects was higher than that of the reference group at the beginning and end of the study.

When looking at each subject's bone mineral content, adjusted for their height, the researchers noticed that bone mineral content in the arms and legs increased less than would be expected with growth while the lumbar spine content increased more than expected. These changes in bone mineral content were largely explained by changes in the amount of fat and muscle in the body during the intensive weight loss program.

“As obesity treatment during adolescence becomes more frequent, it is important to understand the role of weight loss on bone health during this critical period,” Dr. Stettler added.