10 April 2003 23:00 GMT

by Damaris Christensen

The concentration of circulating levels of leptin - a hormone linked to obesity - may prove another indicator of breast cancer risk, according to new research. If future research confirms the link, leptin might become a new factor to consider, alongside weight, family history, and estrogen levels, when calculating a woman's breast cancer risk.

The new findings show that a woman's production of leptin may reveal her history of eating fatty foods. "The amount of leptin found in a woman's blood stream can indicate her accumulation of fat over the years," said lead researcher Richard Hajek, of the University of Texas M.D. Anderson Cancer Center in Houston. "Measuring current body weight and fat intake doesn't offer that kind of a perspective."

Leptin is made by fat cells and overweight people tend to have higher amounts of leptin in their blood stream. Studies of leptin - which suppresses appetite when it is high - have shown that when people are overweight leptin concentrations may vary immensely. But if researchers account for body weight and body fat, Hajek told BioMedNet News, then a strong correlation with diet emerges.

Hajek and his colleagues followed 38 overweight, poste-menopausal women - all Hispanic - 25 of whom were given intensive dietary counseling for six months. After accounting for a woman's weight-to-height ratio and her percentage of body fat, as women ate less fat their leptin levels decreased - suggesting that leptin levels might reflect eating habits over time, says Hajek.

"I think there is a ratchet-type mechanism," he said. "If you overeat, leptin rises in an attempt to control appetite. But if you maintain a high intake over long periods of time, eventually baseline levels go up."

The results were published in the Proceedings for the 2003 Annual Meeting of the American Association for Cancer Research. The meeting itself was cancelled due to an outbreak of a virulent pneumonia in Toronto.

Hajek and his colleagues believe that leptin, in conjunction with known risk factors, may predict a woman's risk of developing breast cancer. To further test this hypothesis, they are now looking at leptin levels in about 3,000 women who have been followed for several years as part of a large study of whether dietary change could affect breast cancer recurrence.

"This is kind of exciting, even though it is a very small study," said Raymond DuBois, director of cancer prevention with the Vanderbilt-Ingram Cancer Center at Vanderbilt University in Tennessee. "We know for most solid tumors that obesity is a risk factor. This study is trying to make that link on a molecular level." Given that leptin levels are known to vary, however, much more research needs to be done to determine how well a single leptin measurement can track long-term changes in diet, he says.

A growing body of evidence suggests that it is time to take a closer look at the relationship of leptin and breast cancer, says Margot Cleary, a nutritional biochemist with the Hormel Institute at the University of Minnesota in Austin, Minnesota. Cleary's work has shown that leptin has a proliferative effect on cancer cells in culture. She's also shown that mice with leptin and leptin-receptor deficiencies are more susceptible to breast cancers.

"As yet, the role of leptin in cancer is not really clear cut," she said, "but it is certainly deserving of further study.".