The dreaded 15 has long been a fear of first-year college females--but now there is even more cause for worry.

Researchers at the Harvard School of Public Health and Brigham and Women's Hospital recently found a correlation between weight gain and an increased risk of breast cancer.

Although the incidence of breast cancer is generally lower for young women, the study showed that maintaining a healthy weight is important throughout young adulthood.

"The message [to young women] should be that they should try to maintain their lean body mass. Weight gain after 18 was associated with breast cancer," said a researcher in the study, Dr. Zhiping Huang, who does research at Brigham and Women's Hospital.

Huang said that the increased risk varies directly with the amount of weight gained.

"The risk is continuous," she said. "The more [weight] you gain, the bigger the risk."

The study found that a weight gain of 45 pounds caused the risk of breast cancer for women aged 30 to 55 to double. But women who gain five to 10 pounds do not need to worry about an increased risk, she said.

According to Huang, physical activity is the most effective way for females to reduce their risk of breast cancer.

"The best approach is regular exercises. For women who are already over-weight, weight loss is recommended," she said.

Estrogen--the hormone linked to breast cancer--increases in the blood stream with a higher amount of body fat.

Huang explained that "after menopause, estrogen is produced by body fat. Weight gain increases blood estrogen levels."

The conclusion reached from this study correlates with earlier studies showing that post-menopausal estrogen or progesterone usage results in a higher risk of breast cancer, according to Huang.

Huang's research is part of a Harvard Nurses' Health study--a study that began in 1976 and has been following women age 30 to 55. Future research plans include studying how the weight distribution affects their risk for breast cancer.

"We are planning to study body fat distributions and risk of breast cancer," Huang said. "Some women gain a lot of weight abdominally. But some women gain weight peripherally."

Based on future studies, doctors may be able to recommend more specific exercises to women based on their body types.

"Maybe women can do some special exercises to change their fat distribution," Huang said.