In 1987, 1992, 2000, and 2005, interviewers asked, "During the past 12 months, did you take any vitamin E?" In 1992, this question and others dealing with the use of particular vitamin/mineral supplements were prefaced with the instruction, "The following questions are about individual vitamins and minerals. Do not include the multi-vitamins you already told me about." The 2000 and 2005 surveys provided similar instructions, which interviewers were instructed to "read if necessary." The 1987 survey included a similar instruction that interviewers were told to read if there had been an affirmative response in VITAMULTV (i.e., if the respondent had taken multi-vitamins in the past 12 months).

In 2002, interviewers asked, "During the past 12 months, did you use high dose or megavitamin therapy for your own health or treatment?" (italics added), rather than asking about vitamin and mineral supplements in general. Those with an affirmative response (i.e., a "Yes" response in VITYR) were shown a flash card containing a list of vitamins and minerals. They were asked, "During the past 12 months, did you take any of the following vitamins in high dose? You may choose more than one" (italics added).

The other such supplements, along with the years these variables are available, are:

• Beta carotene (VITABETA, 2005)

• Calcium (VITACALC, 1987, 1992, 2000, 2002, 2005)

• Vitamin A (only) (VITAMINA, 1987, 1992, 2000)

• Vitamin C (VITAMINC, 1987, 1992, 2000, 2002)

• Multi-vitamin (VITAMULTV, 1987, 1992, 2000, 2002, 2005)

• Selenium (VITASELN, 2002, 2005)

• Coenzyme Q-10 (VITYCOEN, 2002)

• DHEA (VITYDHE, 2002)

• Vitamins A and/or D (VITYVITAD, 2002)

• Vitamin B complex (VITYVITB, 2002)

• Zinc (VITYZINC, 2002)

In 1987, 1992, 2000, and 2005, respondents who gave an affirmative response to the question associated with VITAMINE were asked to report the number of months they had taken vitamin E supplements (VITAMINEMO).

In 1987 only, respondents were asked to report the number of vitamin E pills they took per day (VITYVITEPILS) and the number of international units (IU) of vitamin E per pill (VITYVITEUN).

In 2000 and 2005, respondents who had taken vitamin E during at least one month in the past 12 months were asked how often they had taken vitamin E in those months (VITAMINENO), responding as desired in terms of days per week or days per month (VITAMINETP).

For 2000 (but not 2005), the National Center for Health Statistics recoded data from VITAMINENO and VITAMINETP to create two new variables with consistent time units: number of days per week took vitamin E during the relevant months of the past 12 months (VITAMINEDWK), and number of days per month took vitamin E during the relevant months of the past 12 months (VITAMINEDMO). VITAMINEDMO is also available for 1987 and 1992, when this information was collected through a direct question (i.e., "About how many days per month did you take vitamin E?").

For more information on the full range of variables dealing with vitamins, see VITANY and VITYR.

The 2002 Field Representative's Manual defines such therapy as "the use of vitamins in excess of the Recommended Daily Allowances (RDA) established by the National Academy of Sciences, Food and Nutrition Board."

Thus, an affirmative response to VITAMINE in 2002 indicates that the sample adult took vitamin E in high doses. A negative response to VITAMINE in 2002 indicates that the respondent did not take high doses of vitamin E, but does not indicate that he/she took no vitamin E at all in the past 12 months. By contrast, affirmative responses to VITAMINE in 1992, 2000, or 2005 indicate that the respondent took any amount of vitamin E (other than in a multi-vitamin) in the past 12 months.

RDAs vary by age group, sex, and pregnancy/lactation status. In 1987, the highest RDA of any group for vitamin E was 15 international units (or 10 milligrams). Thus, any respondent in 1987 taking more than 15 IU of vitamin E in a day would have been considered to be using "high dose or megavitamin therapy" by the standard set for the 2002 NHIS.

However, by 2002, RDAs were replaced by the Dietary Reference Intakes (DRI)--a set of dietary recommendations from the Food and Nutrition Board of the Institute of Medicine. The DRI for vitamin E was established as 15 milligrams (not IU) per day. According to the Council for Responsible Nutrition, "Historical vitamin E conversion factors were amended in the [Dietary Reference Intake report, 1997-2001], so that 15 mg is defined as the equivalent of 22 IU of natural vitamin E or 33 IU of synthetic vitamin E." (https://www.crnusa.org/about_recs3.html) Thus, a researcher wishing to impose a uniform threshold to establish what counts as "high dose or megavitamin therapy" for 1987 and 2002 may want to set 22 IU or 33 IU as the threshold for 1987, rather than 15 IU, which was the maximum RDA at the time.

Researchers who wish to combine data on vitamin E intake from 1987 with that from 2002 should exercise caution because there is more precision available in the variables from 1987 than in the variables from 2002. In the former year, respondents only provided the dosage amount of vitamins and minerals if they volunteered to get their container of supplements and read the dosage of vitamin E to the interviewer. In 2002, by contrast, "high dose or megavitamin therapy" was user defined to the extent that, although a definition of such therapy was provided in the Field Representative's Manual, the definition was not routinely shared with respondents. Further, respondents were not routinely reading the dosages of the supplements they were taking from a container in 2002.