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The way a girl grows during adolescence, and even in the womb, may play a role in her risk of breast cancer later in life, a Danish study suggests.

The study of the health records of 117,000 women in Denmark found that those who were chubby at birth but tall and lean by age 14 were more likely to develop the disease.

"Something very early on in life plays a role in [the] risk of breast cancer," said lead researcher Mads Melbye, professor of epidemiology at the State Serum Institute in Copenhagen.

"No one knows really what," he said, but theories include differences in levels of hormones that influence growth, and genetic variations that dictate people's size.

Most studies of women have found that tall ones have an increased risk of breast cancer, that heavy ones have a higher risk of the disease after menopause, and that lean ones have a higher risk before menopause and a reduced risk after.

"We as researchers need to focus earlier in life to disentangle what really matters," Dr. Melbye said.

The study is reported in today's New England Journal of Medicine.

The researchers found that the taller a girl was at 14, roughly the end of puberty, the higher her chance of later developing breast cancer. For example, a girl 5 feet 6 inches tall at age 14 had about a 50-per-cent higher risk of later developing breast cancer, compared with one who was just under 5 feet at 14.

Babies who weighed 8.8 pounds at birth had a 17-per-cent higher risk of later developing breast cancer than newborns who were only 5½ pounds. Each additional two pounds over 5½ boosted risk by 10 per cent.

The lower a girl's body mass index (a measure of weight relative to height) at age 14, the higher her risk of breast cancer, echoing findings about the risk in premenopausal women. The Danish researchers also found the younger a girl has her peak growth period, the higher her risk of later breast cancer. "It is confirming things that people had long suspected," said Dr. William Hait, director of the Cancer Institute of New Jersey.

He said factors that influence initial development of breast tissue in the womb and how early a girl's breasts develop, as well as what a pregnant woman eats and drinks, and her daughter's diet during childhood, appear to affect the risk of breast cancer.

One surprise was that, after adjusting for the other risk factors, the researchers found that the age at which a girl began menstruating did not influence her risk of breast cancer. It has long been dogma among doctors that the earlier menstruation begins and the later menopause starts, the higher the risk of breast cancer.

Dr. Hait and Dr. Yelena Novik, a breast cancer specialist at New York University Cancer Center, said the Danish study was particularly strong because of the huge number of files studied and the detailed school and adult health records available in Denmark. But Dr. Novik said it would have been helpful if the study had examined the women's weight and height as adults and whether they had a family history of breast cancer.