The Nurses’ Health Study

The Study

The Nurses’ Health Study began in 1976 and has followed generations of nurses for decades. The original cohort included 121,700 female registered nurses between ages 30 and 55 at enrollment.

Links to This Study

• Official Nurses’ Health Study history
  The study’s official history page explains how the original cohort was established, how participants have been followed, and how the research focus expanded over time.
• Selected Nurses’ Health Study publications
  The official study website maintains a large collection of scientific papers produced from the Nurses’ Health Studies.

How Did the Study Begin?

In 1976, researchers mailed questionnaires to registered nurses across the United States. A total of 121,700 women returned completed questionnaires and became the original Nurses’ Health Study cohort.

The women were 30 to 55 years old when they entered the study.

Why Nurses?

Registered nurses were especially useful participants for a long-term health study because they could understand detailed medical questions and were expected to report health information reliably.

The original study focused on issues including contraceptive use, smoking, cancer, and cardiovascular disease, but its scope expanded enormously over time.

How Were the Women Followed?

Participants have generally received follow-up questionnaires every two years. Researchers ask about newly diagnosed diseases, medications, smoking, physical activity, reproductive factors, and many other aspects of health and lifestyle.

Because the same participants are followed repeatedly, researchers can examine how exposures measured years earlier relate to diseases that develop much later.

When Was Diet Added?

Detailed dietary information was added in 1980 using a food-frequency questionnaire.

Dietary questionnaires have subsequently been repeated at approximately four-year intervals, allowing researchers to study changes in eating patterns over time rather than relying on a single dietary measurement.

Why Is This Study So Important for Nutrition Research?

Many chronic diseases take decades to develop. A short clinical trial cannot practically follow tens of thousands of people for most of their adult lives.

A large prospective cohort such as the Nurses’ Health Study allows researchers to examine long-term associations between habitual diet and later development of cardiovascular disease, diabetes, cancer, and many other outcomes.

Examples of Nutrition Questions Studied

Researchers using Nurses’ Health Study data have examined many nutrition questions, including dietary fats and coronary heart disease, fruit and vegetable intake, type 2 diabetes, red and processed meats, beverages, dietary patterns, and healthy aging.

The study has produced an enormous number of scientific publications rather than one single “Nurses’ Health Study paper.”

One Landmark Nutrition Paper

A 1997 analysis published in the New England Journal of Medicine followed 80,082 women from the Nurses’ Health Study and examined dietary fat intake and coronary heart disease risk.

• PubMed record — 1997 dietary-fat paper
  The U.S. National Library of Medicine’s record for the landmark paper Dietary Fat Intake and the Risk of Coronary Heart Disease in Women.
• DOI — permanent study identifier
  The DOI is the paper’s permanent digital identifier and should continue to direct readers to the official journal page even if the journal’s web address changes.
• Official journal page — New England Journal of Medicine
  The official publisher page for this landmark Nurses’ Health Study nutrition analysis.

What Are the Strengths of the Nurses’ Health Study?

Its major strengths include its very large cohort, decades of follow-up, repeated measurements of diet and lifestyle, high participant retention, and detailed information about many potential confounding factors.

These features allow researchers to examine relationships that would be extremely difficult or impossible to study in long-term randomized trials.

An Important Limitation

The Nurses’ Health Study is observational. Researchers observe what participants eat and how their health changes; they do not randomly assign women to different lifelong diets.

For that reason, associations found in the study cannot by themselves prove that a particular food or dietary pattern caused or prevented a disease. Researchers adjust statistically for many potential confounding factors, but unmeasured differences may remain.

Who Was Included?

The original cohort consisted of female registered nurses, primarily in the United States. That made long-term follow-up practical and scientifically valuable, but it also means that the original cohort was not a perfect cross-section of the entire population.

Later Nurses’ Health Study cohorts expanded the age range and diversity of participants.

The Nurses’ Health Study II and III

The Nurses’ Health Study II began in 1989 with more than 116,000 younger female nurses. Nurses’ Health Study 3 began in 2010 and includes a newer generation of nurses and nursing students.

Together, the Nurses’ Health Studies form one of the largest and longest-running programs investigating how diet, lifestyle, reproductive factors, environment, and other exposures relate to long-term health.

Why Is This Included Under “What Happens Over a Lifetime?”

The great value of this study is time. Researchers have been able to watch health patterns unfold over decades.

That long perspective helps answer questions that short trials cannot: whether everyday eating and lifestyle patterns are associated with health and chronic disease many years later.