In 1991, the mailed questionnaire included a 133-item semiquantitative
food frequency questionnaire. Women were asked how often they had consumed
a commonly used unit or portion size of each food on average over the previous
year, including 3 items on consumption of sugar-sweetened soft drinks ("Coke,
Pepsi, or other cola with sugar," "caffeine-free Coke, Pepsi, or other cola
with sugar," and "other carbonated beverages with sugar"), 4 items on fruit
juice ("apple juice," "orange juice," "grapefruit juice," and "other juice"),
1 item on fruit punch, and 3 items on diet soft drinks ("low-calorie cola
with caffeine," "low-calorie caffeine-free cola," and "other low-calorie beverages").
We summed the intake of single items to create a total of sugar-sweetened
soft drink, diet soft drink, and fruit juice consumption. The 9 possible responses,
ranging from "never" to "6 or more times per day," were aggregated into 4
categories (<1 drink per month, 1-4 drinks per month, 2-6 drinks per week,
and ≥1 drink per day). Similar questionnaires were used to collect dietary
information in 1995 and 1999. Nutrient intakes were computed by multiplying
the frequency response by the nutrient content of the specified portion sizes.
Values for nutrients were derived from the US Department of Agriculture sources14 and supplemented with information from manufacturers.
The validity and reliability of food frequency questionnaires similar to those
used in the Nurses' Health Study II have been described elsewhere.15,16 Briefly, the correlation coefficients
between questionnaire and multiple dietary records were 0.84 for cola-type
soft drinks (sugar-sweetened and diet combined), 0.36 for other carbonated
soft drinks, 0.84 for orange juice, and 0.56 for fruit punch in the Nurses'
Health Study I15 and were 0.84 for sugar-sweetened
cola, 0.55 for other sugar-sweetened soft drinks, 0.73 for diet cola, 0.74
for other diet soft drinks, 0.78 for orange juice, 0.77 for apple juice, 0.75
for grapefruit juice, and 0.89 for other fruit juices in the Health Professionals
Follow-up Study,16 2 similar cohort studies
among US health care professionals.