The connection between cortisol and obesity, touted by TV ads for a variety of weight-loss supplements, may be even more tenuous than first thought, according to researchers at Oregon Health & Science University.

The conventional wisdom for some time has been that the stress hormone cortisol increases appetite and stimulates adipose tissue to store fat, primarily in the abdomen. And in recent years, there has been a boom in weight-loss supplements known as cortisol blockers.

But a new study by the Oregon researchers, reported in the Journal of Clinical Investigation, suggests that cortisol levels are not the sole, major factor involved in obesity and fat distribution.

"In reality, there are many other hormones involved in weight regulation and it's hard to say whether cortisol and corticosterone -- both in a family of hormones called glucocorticoids -- rise prior to weight gain or if their increases are impacts of the weight gain itself," said Dr. Malcolm Low, associate director of the Center for the Study of Weight Regulation and Associated Disorders.

In their research, scientists studied specially bred mice lacking the proopiomelanocortin (POMC) gene. Previous research has shown that mutations to the POMC gene in humans and mice cause obesity, but simultaneously decrease glucocorticoid levels.

Because it was unknown whether the primary abnormality occurs in the brain or peripheral tissues, scientists attempted to repair the problem and counteract the obesity by manipulating POMC and glucocorticoid levels.

"In both cases, the mice lacking POMC in the brain did not show improvement in their metabolic state. The treatments actually led to an acceleration in weight gain and development of diabetes," explained Low.

"Importantly, the identical treatments had no discernable effect in control mice with normal POMC levels in the brain. This research demonstrates the important function of the POMC gene in the central nervous system, independent of the pituitary and adrenal glands.

"It also demonstrates that cortisol alone is not the major culprit in weight gain. Glucocorticoids are merely part of a chain of hormonal and neuronal signals associated with obesity," Low concluded.