However, whether these findings translate into a lower risk of breast cancer later in life is not clear, according to the report in the January 15th issue of the Journal of the National Cancer Institute ( news - web sites).

"Although we do not know if lower hormone levels during adolescence will influence breast cancer risk in adulthood, adolescence is a time of rapid growth and maturation of the breasts. Estrogens and progesterones contribute to the regulation of this process," Dr. Joanne F. Dorgan, the study's lead investigator, said in a prepared statement.

Therefore, lower hormone levels might slow down the rate of cell division, which can lead to cancer-causing mutations, explained Dorgan, who is with the Fox Chase Cancer Center in Philadelphia, Pennsylvania.

Elevated body fat is another risk factor for premenopausal breast cancer, although it is not clear how extra pounds may contribute to the risk.

To investigate the relationship between fat intake during puberty and blood levels of hormones associated with breast cancer, the research team studied 286 girls aged 8 to 10 years. The girls were already enrolled in a study testing a diet to lower levels of LDL or "bad" cholesterol.

About half of the group attended individual and group nutrition counseling sessions on how to follow a low-fat diet, in which 28% of calories came from fat and no more than 8% from saturated fat. General nutrition guidelines suggest that healthy adults consume no more than 30% of total calories from fat, of which a maximum of 10% is from saturated fat.

The other half of the group received written material from the American Heart Association ( news - web sites) and did not take part in nutrition counseling.

After five years, girls in the counseling group had lower levels of specific forms of estrogen linked to breast cancer. For instance, estradiol levels were about 30% lower and estrone levels were about 20% lower, the study found. Levels of progesterone, which may also increase the risk of breast cancer, were also lower, the study found.

Finally, these girls reported eating fewer calories, less fat and saturated fat, and more fiber, compared with girls in the other group. These dietary interventions may also lower breast cancer risk, although study findings have been mixed.

"These results suggest that the modest reductions in total fat, saturated fat, and perhaps energy intake during adolescence may alter the function of the hypothalamic-pituitary-ovarian axis, which regulates ovarian hormone production," researchers conclude.

"Whether these differences ultimately influence breast cancer risk is currently unknown."

SOURCE: Journal of the National Cancer Institute 2003;95:132-141.