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Beth Mancini, MSN, RN, has counted the number of freckles from her knees to her ankles, mailed her own blood and urine samples and filled out personal health questionnaires every other year for more than a decade.

Women who are younger than this Texas nurse will benefit most from the research project that requires such personal information from Mancini. She is one of more than 200,000 nurses throughout the country who are participating in the Harvard Nurses' Health Study-the largest, longest-running study of women's health in the world. Nurses such as Mancini hope that their faithful participation will answer questions that will help younger generations maximize their chances of enjoying long, healthy lives.

Frank Speizer, MD, launched the first phase of the Nurses' Health Study in 1976 to investigate the long-term effects of birth control pills on women. Researchers knew the pill was an effective contraceptive, but Speizer noticed increasing reports of healthy young women who suffered from blood clots in their legs and lungs.

Speizer knew he needed a cohort of women who had been regularly using the pill. At first, he considered studying the wives of physicians, but decided it would be easier for medically trained women to understand terminology in the questionnaires.

The researchers contacted the boards of nursing in 11 states and tracked down the addresses of thousands of female, married nurses aged 30 to 55. They sent health questionnaires to 170,000 nurses and 120,000 responded.

In 1989, Speizer's team launched another study to investigate women who were taking more modern birth control pills, which had lower hormone levels than the original ones. The researchers wanted to study women who had started taking these newer pills at an earlier age. They recruited another 116,000 nurses aged 25 to 42.

As the researchers followed the nurse participants' eating and exercise habits, their disease patterns and family histories, they discovered common themes in the data.

"We found that what our grandmothers told us was correct," Speizer said. "Don't smoke, keep your blood pressure down, don't gain weight, take a multivitamin with folate and exercise regularly."

The data showed that exercise reduces the risk of colon cancer and heart disease, and vitamins with folate have a protective effect on the heart and colon. Women who eat less red meat also generally have a lower risk of colon cancer.

The researchers also found that women who take the pill for more than five years will modestly increase their risk of breast cancer, but this risk subsides after they've been off the pill for 10 years.

"Most women use the pill when they are not at high risk of breast cancer," said Susan Hankinson, Sc.D., RN, senior investigator for the study. "The pill also can decrease the risk of ovarian and endometrial cancer."

The researchers also found that postmenopausal hormones generally don't increase the risk of breast cancer if women take the hormones for less than five years. But the longer a woman uses them, the more likely she is to develop breast cancer.

The Nurses' Health Study also showed that vigorous exercise is not required to ward off heart disease.

According to the data, women who walk briskly for at least three hours a week are protected against heart disease as much as women who exercise vigorously for 90 minutes a week. Both groups are 30 percent to 40 percent less likely to develop heart disease than sedentary women.

One of the researchers' unexpected discoveries debunked the idea that all fats are harmful.

The fats in processed snacks and margarine can clog the arteries, but the fats in fish and nuts actually can reverse the damage done by the harmful fats. Although eggs have a bad rap for their cholesterol content, the Nurses' Health Study found that the risk of heart disease was the same in women who ate an egg a day as for those who ate one egg per week.

Nurse participants such as Bonnie Faherty, Ph.D., FNP, RN, believe the study's findings are exciting, but she admitted that it can be challenging to change old habits.

"When they want information for a questionnaire, it's a real call to your conscience," said Faherty, who has participated since 1989. "As nurses, we have to be role models for our patients. I've tried to cut down on sugar and fat, and I'm more aware of how much red meat I eat. But I'm not a great fish eater."

Faherty had bouts of colon and breast cancer, but still participates in the study. "I just like the idea of being part of a research study that is so large and could produce such important results," she said.

Speizer said the nurses have been incredibly helpful by notifying researchers when their addresses change, and more than 90 percent of the original nurses still participate. "The nurses themselves have been extremely cooperative and tell us an awful lot about themselves," Speizer said.

Sixty-eight-year-old Marie Phillips, RN, has been in the study since 1976, and she's pleased that nurses have gained the reputation of being persevering participants. She believes that the most fruitful data are yet to come.

"Many of the things are still to be discovered," Phillips said. "When I die or other nurses die, then they will see what really happens in the long run. If I'm healthy and live to be 100, they can look at my health profile and see what was it was that I may have done right."