Assessment of Supplement Use

The baseline questionnaire asked participants about the frequencies with which they used three types of multivitamins ("stress-tab type", "therapeutic or theragran type", and "one-a-day type") during the preceding 12 months. For each type of multivitamin, participants were asked to report frequency of use as never, less than one time per week, one to three times per week, four to six times per week, or every day. Each frequency category was assigned a single value (never = 0, less than one time per week = 0.5, one to three times per week = 2, four to six times per week = 5, and every day = 7). Multivitamin use was defined as the sum of the values obtained for each type of multivitamin and was categorized as never use, casual use (between zero and six times per week), consistent use (seven times/wk), or heavy use (more than seven times per week). Thus, a participant who reported using a stress-tab type one to three times per week and a one-a-day type four to six times per week was considered to have been consuming multivitamins seven times/wk. Participants were also queried regarding dose and frequency of use of single supplements including vitamin A, beta-carotene, vitamin C, vitamin E, and calcium. Daily dose for vitamin E supplement intake was calculated as dose x daily frequency (frequency of use options were the same as multivitamins, and dose options were <100, 100–250, 300–500, ≥600 IU, or unknown). Each category of dose was assigned as 100, 200, 400, and 800 IU, and for those answering "unknown", a value of 400 IU was assigned. For those taking a multivitamin, daily dose of supplemental vitamin E was assumed to be 30 IU. Use of iron, zinc, selenium, and folic acid was assessed by asking participants whether or not they used each of these individual supplements more than once per month in the past 12 months (yes or no).

***They also had questions about diet. Full article:

http://jnci.oxfordjournals.org/cgi/c...7a92e7153#SEC2