Dietary Analyses in the Nurses' Health Study, Nurses' Health Study II, and Health Professionals Follow-Up Study

The Nurses' Health Study (NHS) consisted of 121,700 female registered nurses aged 30 to 55 years from 11 US states who were enrolled in 1976. The NHSII was initiated in 1989 with the recruitment of 116,671 younger female registered nurses, 24 to 44 years of age, from 14 states. The Health Professionals Follow-up Study (HPFS) was established in 1986 and was comprised of 51,529 US male health professionals ranging in age from 40 to 75 years at enrollment from 50 states.

Study investigators sent follow-up questionnaires biennially to participants to update information on past medical history as well as lifestyle factors. Validated food frequency questionnaires (FFQs) were first sent in 1980 for the NHS, 1991 for the NHSII, and 1986 for the HPFS. Dietary assessments have been updated every 2-4 years since baseline. The FFQs collect information on average intake of each food item over the past year. It also specifies a common serving size for each item. Participants could select from one of nine intake frequency choices, ranging from less than once per month to six or more times per day. Participants also provided information on current use and dose of multivitamins and use of other vitamin supplements.

For these three cohorts, investigators repeatedly collected and updated information on several anthropometric and lifestyle factors such as weight, smoking status, alcohol use, coffee intake, and physical activity level. Information was also collected on several major risk factors.

Study subjects reported new diagnoses biennially. After obtaining permission from participants, their medical and pathological records were acquired. Study physicians blinded to questionnaire information reviewed these records to confirm diagnoses of coronary heart disease and stroke. Self-reported diabetes diagnoses are confirmed using a validated supplementary questionnaire on symptoms, blood glucose levels, and medication use. Deaths are identified through reports from next of kin, postal authorities, or by searching the National Death Index.

All investigations regarding dietary factors in relation to type 2 diabetes, cardiovascular disease, and mortality have been approved by the institutional review boards of both Brigham and Women's Hospital and Harvard T.H Chan School of Public Health.

Inclusion criteria

• Returned baseline food frequency questionnaires (FFQs).

Exclusion criteria

• Participants who had died or reported a diagnosis of diabetes (including type 1 diabetes, type 2 diabetes, and gestational diabetes for women), cardiovascular disease (CVD) or cancer at and before the baseline for the dietary analyses.
• Participants who left more than 70 of the 131 food items blank on the baseline FFQ, reported unusual total energy intake levels (<3,347 or >17,573 kJ/day for men, and <2,092 or >14,644 kJ/day for women), or had missing baseline dietary information.
• Participants who only completed the baseline questionnaire.