New York, Nov 22 (IANS): Teenagers who are obese as well as those who lose excessive weight may both be at risk of irreparable damage to their bones, a new study has found.

Obesity has been previously associated with the risk of cardiovascular diseases and diabetes, but the study found that it can also affect the bone structure in childhood and adolescence.

"While obesity was previously believed to be protective of bone health, recent studies have shown a higher incidence of forearm fractures in obese youth," said lead author Miriam A. Bredella, Associate Professor at Harvard Medical School in Boston, US.

Having a high amount of visceral fat -- the deep fat in the abdomen that surrounds the internal organs -- coupled with a low amount of muscle mass -- anorexia nervosa -- puts adolescents at risk for weakened bone structure, the study said.

"Visceral fat secretes substances that promote chronic inflammation, and chronic inflammation stimulates formation of osteoclasts, which are the cells that resorb or break-down bone. In addition, vitamin D, which is important for bone health, is soluble in adipose tissue and gets trapped within fat cells," Bredella said.

Growth hormone, which is important for bone health, is also lower in adolescents with visceral obesity.

On the other hand, anorexia nervosa also leads to an increased fracture risk in adolescence, which persists to adulthood, even after normalisation of body weight, Bredella said, adding that it is important to address this problem early on.

Lean mass was positively associated with trabecular density -- a marker for the risk of osteoporosis --, volume and integrity.

"The best way to prevent bone loss is a healthy diet that contains adequate amounts of calcium and vitamin D, along with sufficient exercise," Bredella said.

The study will be presented at the annual meeting of the Radiological Society of North America in Chicago, US.