Nurses Health Study

The Nurses Health Study (NHS) and its successor, the NHS II, are two of the largest prospective (for-ward-looking) studies ever conducted. The primary purpose of the studies is to investigate the risk factors for major chronic diseases among women. The original NHS study began in 1976 and was motivated by an interest in assessing the safety profile of oral contraceptive, which millions of women had recently begun taking. Approximately 122,000 married registered nurses between the ages of 30–55 were enrolled [Page 1255]in the study and were asked to fill out questionnaires every two years. Topics initially included smoking, hormone use, and other chronic disease parameters. Eventually, other components were added including diet and nutrition assessments, quality-of-life measures, and blood and toenail samples. In the NHS II study, launched in 1989, investigators were interested in looking for contraceptive–cancer links in a younger cohort of women who may have begun oral contraceptives in adolescence. Approximately 116,000 registered nurses between the ages of 25 and 42 were included in this study, which measured a similar series of parameters as the NHS I. The NHS studies were based at Boston-area hospitals and funded by the U.S. National Institutes of Health.

Over the past 30 years, the NHS has produced a wealth of epidemiological data on a wide range of topics. Some of the major findings from the first 20 years of the NHS are as follows:

• 1.
  Cigarette smoking is a major cause of heart disease and stroke, with the risk dropping significantly in those who quit smoking. Smoking is also associated with lung cancer, suicide, cataracts, diabetes, hip fractures, and colon cancer, but not breast cancer. Those who quit tend to gain about 6 pounds, on average, and their risk of death from any cause returns to that of a nonsmoker 10 to 14 years after quitting.
• 2.
  Current oral contraceptive use is associated with a small increase in breast cancer and cardiovascular disease risk, but not colon cancer, hip fractures, or diabetes. Hormone replacement therapy for more than five years was associated with a small increase in breast cancer risk, but a decrease in cardiovascular disease risk (this finding has since been challenged) and decreased risk of hip fractures.
• 3.
  Obesity was found to be strongly associated with increased risk of cardiovascular disease, diabetes, and gallstones; a weak association with colon cancer and breast cancer (now controversial); and a protective effect on risk for hip fractures.
• 4.
  Moderate alcohol use was found to be related weakly to breast cancer, colon polyps, and hip fractures, but it had a protective effect for diabetes, it decreased total mortality among older women, and it decreased cardiovascular disease risk.
• 5.
  Certain dietary habits were found to be protective for or to increase risk for certain conditions including red meat increases colon cancer risk, trans fats increase cardiovascular risk, increased caffeine intake increases hip fracture risk, and vitamin E was found to be protective for cardiovascular disease but not for breast cancer.
• 6.
  Other disease associations were documented, including shift work and cardiovascular disease, vigorous activity decreases diabetes risk, blistering sunburns increase melanoma risk, family history of breast or colon cancer increases the risk of those diseases.

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