FRIDAY, April 8 (HealthDay News) -- A lack of leptin contributes to the absence of menstrual periods in women with extremely low levels of body fat, but treatment with a synthetic form of the hormone may restore both the menstrual cycle and fertility, a new study indicates.

Extremely low levels of body fat can occur in women who are unusually active, such as runners and dancers, and in those with eating disorders. These women are prone to the absence of periods (known to doctors as hypothalamic amenorrhea, or HA), which can lead to infertility and osteoporosis.

Previous research found that women with HA have chronically low serum leptin levels. This new study, published online in the Proceedings of the National Academy of Sciences, is the first to offer definitive proof that a lack of leptin contributes to HA.

The randomized, double-blind study included 20 women, ages 18 to 35, with HA. Many of them were runners. Over 36 weeks, the women received daily injections of either a synthetic form of leptin called metreleptin or a placebo, without the participants or the researchers being aware who was receiving the real or sham therapy.

Within one month of starting treatment, the women who received the metreleptin showed significantly increased levels of leptin.

"Seven of 10 women began to menstruate and four of the seven were found to be ovulating," senior author Dr. Christos Mantzoros, director of the Human Nutrition Unit at Beth Israel Deaconess Medical Center and a professor of medicine at Harvard Medical School, said in a BIDMC news release.

"Compared with women who received the placebo, the women who received the metreleptin therapy were also found to have an improved hormonal profile and exhibited higher levels of biomarkers indicating new bone formation," he added.

The synthetic leptin used in the study, which was funded in part by the National Institutes of Digestive and Kidney Diseases, was provided by Amylin Pharmaceuticals, Inc.

More information

The U.S. National Institute of Child Health and Human Development has more about amenorrhea.