A hormone that triggers hunger may also play a role in the reproductive system, new research suggests.

The hormone, known as ghrelin, may be involved in suppressing reproductive function when a woman is not eating enough, researchers say.

Ghrelin is known as the hunger hormone because people given the hormone in previous experiments became so hungry that they ate up to one third more food than usual.

In normal-weight people, ghrelin levels surge before meals and decline afterward. This cycle is thrown off balance in people who weigh too much or too little, however. People who are obese tend to have below-average levels of the hormone, while levels of the hormone are above average in people with the eating disorder anorexia nervosa.

Scientists think that ghrelin levels rise in anorexics to signal that the body is not getting enough energy.

Among women with anorexia who have stopped having their menstrual period - a condition called amenorrhea - ghrelin levels have been shown to be above normal, but levels of the hormone tend to decline in anorexics who have started gaining weight.

Like anorexia, exercise can sometimes interfere with the menstrual cycle, so a team led by Dr. Mary Jane De Souza at the University of Toronto in Canada set out to measure ghrelin levels in physically active women.

The study included 32 women who exercised regularly. Some of the women had normal menstrual cycles, while others had amenorrhea. Other physically active women had periods, but they didn’t ovulate.

For comparison, the study also included several sedentary women with normal menstrual cycles.

Levels of ghrelin were about 85 percent higher in physically active women who were not menstruating, De Souza and her colleagues report in the July issue of the Journal of Clinical Endocrinology and Metabolism. But ghrelin levels were normal in women who were menstruating but not ovulating.

The rise in ghrelin levels may reflect a chronic energy deficiency in female athletes who have stopped menstruating, De Souza told Reuters Health. The surge in ghrelin may be signaling the body to eat more, she said.

“It appears that the body may well have compensatory mechanisms that are responding in attempts to increase food intake to offset the energy deficiency associated with severe menstrual disturbances such as amenorrhea,” De Souza said.

She noted that other studies have shown that female athletes who restrict their food intake often do so voluntarily, typically to improve performance or for aesthetic reasons. “The restoration of adequate food intake has been shown to reverse amenorrhea regardless of exercise levels,” De Souza said.

Ghrelin may also play an evolutionary role, preventing pregnancy during times of food shortages. As the authors put it in their article, their findings support the idea of a “potential role for ghrelin in the complete suppression of reproductive function in extreme states of chronic energy deficiency.”

SOURCE: Journal of Clinical Endocrinology and Metabolism, July 2004.