The Nurses' Health Study is a series of prospective studies that examine epidemiology and the long-term effects of nutrition, hormones, environment, and nurses' work-life on health and disease development. The studies have been among the largest investigations into risk factors for major chronic diseases ever conducted. The Nurses' Health Studies have led to many insights on health and well-being, including cancer prevention, cardiovascular disease, and type 2 diabetes. They have included clinicians, epidemiologists, and statisticians at the Channing Laboratory (of Brigham and Women's Hospital), Harvard Medical School, Harvard School of Public Health, and several Harvard-affiliated hospitals, including Brigham and Women's Hospital, Dana–Farber Cancer Institute, Children's Hospital Boston, and Beth Israel Deaconess Medical Center.
Cohorts
The Nurses' Health Study original cohort was established in 1976 by Frank E. Speizer. Initially, the study investigated contraceptive use, smoking, cancer, and cardiovascular disease. The 1976 baseline group included married female registered nurses between the ages of 30 and 55. Approximately 121,700 participants in 11 of the most populous U.S. states (California, Connecticut, Florida, Maryland, Massachusetts, Michigan, New Jersey, New York, Ohio, Pennsylvania, and Texas) responded. The survey was then distributed biennially thereafter. Over the years, the principal investigator of the Nurses' Health Study have been Frank Speizer, Graham Colditz, Sue Hankinson, and Meir Stampfer. Over time, the study expanded. Most notably, a dietary questionnaire was added in 1980 due to investigators recognizing the impact of diet and nutrition on the development of chronic disease. Blood, urine, saliva, and other physical samples were received and tested beginning in 1982. Experimenters followed up reports of morbidity using the National Death Index. Where possible and permitted, cancer diagnoses were reviewed. Although reports of other diseases were not followed up, self-reporting has been confirmed by medical records and doctors unaware of the answers to the study's questions. The Nurses' Health Study II was established in 1989 by Walter Willett, who has been its principal investigator since inception. The focus of the study was women's health, especially the long term adverse effects of oral contraceptives. The sample population contained females within the age range of 25–42, employed as nurses, from 14 U.S. States. Data collected included the brand of pill and length of use. Over time, the study expanded to include information on basic practices and measurements of health, such as exercise practices and food intake. Between the years of 1996 and 1999, approximately 30,000 nurses volunteered to provide blood and urine samples to the study. Of these women, 18,500 were pre-menopausal, providing samples at specific points in the menstrual cycle. These data allowed researchers to study how hormone levels influence the risk of disease. A second set of samples was collected from 16,500 of the same group of women in 2010–2012, by which time most of them were postmenopausal. Over 25,000 children of women in the Nurses' Health Study II cohort were enrolled in their own follow-up study called the Growing Up Today Study, or GUTS, which has followed the subjects through their early life so as to obtain a second generation of data. The Nurses' Health Study 3 was developed in 2010 by Drs. Jorge Chavarro, Walter Willett, Janet Rich-Edwards, and Stacey Missmer. The study includes investigators from the Channing Division of Network Medicine at Brigham and Women's Hospital, Harvard Medical School, and Harvard T.H. Chan School of Public Health. The original population contained females 19–49 in age and expanded to include Canadian subjects. Unlike the predecessor studies, the NH3 includes participants of both male and female genders in 2015. Jorge Chavarro has been the principal investigator of Nurses' Health Study 3 since its 2010 inception.
Findings The studies revealed many correlations, that is statistical relationships, whether causal or not, between environmental factors and risk for health conditions. Smoking: correlated to a higher likelihood of cardiovascular disease (CVD), colorectal and pancreatic cancer, psoriasis, multiple sclerosis, type 2 diabetes, and eye disease. Trans Fats: correlation between cardiovascular disease (CVD) and consumption of trans fatty acids. Initially met with skepticism, it ultimately led to trans fat being added to U.S. food labels in 2003 and partially hydrogenated oils being labeled as not generally recognized as safe (GRAS) by the FDA. Obesity: correlated to a higher likelihood of cardiovascular disease (CVD), breast cancer, pancreatic cancer, psoriasis, multiple sclerosis, gallstones, type 2 diabetes, and eye disease. Postmenopausal Hormone Therapy: correlated to a lower likelihood of cardiovascular disease (CVD). Combination hormones (progesteron and estrogen) were associated with higher risk of breast cancer. Oral Contraceptives: correlated to a lower likelihood of ovarian cancer. No statistically significant effects of oral contraceptives were observed in regard to risk of breast cancer. Present or past use did not correlate significantly with CVD. Exercise: correlated to higher likelihood of breast cancer survival. Physical activity was correlated to a decreased likelihood of cardiovascular disease (CVD) and type 2 diabetes. Many relationships and factors were examined over the course of the study, examples including diet, coffee consumption, and sleep. Many publications diverse findings were produced as a result.
History
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