In 1987, if respondents had an affirmative response in VITAMULTV (i.e., if they had taken multi-vitamins in the past 12 months), interviewers initially stated, "The following questions are about vitamins not including the multiple vitamins you already told me about." Interviewers then asked direct questions about specific vitamins and minerals (e.g., "During the past 12 months, did you take any calcium?"). The 1987 Field Representative's Manual instructed interviewers to "include only 'Tums' as calcium if reported in question 6. Do not include other brands of antacid."

In 1992, interviewers again began with a statement that the following questions would refer to individual vitamins and minerals, not to multi-vitamins. In 1992, the Field Representative's Manual instructed interviewers to accept "'Rolaids,' 'Tums' or other calcium-rich substances" as a "Yes" response.

In 2000 and 2005, interviewers asked, "During the past 12 months, did you take calcium?" Interviewers were instructed to "read if necessary," "Do not include any calcium in the multi-vitamins you told me about. Include Tums. Do not include milk or calcium-fortified orange juice."

First, 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. Second, rather than posing a question about each vitamin or mineral supplement in turn, in 2002 interviewers showed a flash card containing a list of vitamins and mineral to respondents with an affirmative response to their first question (i.e., a "Yes" response in VITYR). Interviewers then 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)

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

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

• Vitamin E (VITAMINE, 1987, 1992, 2000, 2002, 2005)

• 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 VITACALC were asked to report the number of months they had taken calcium supplements (VITACALCMO).

In 1987 only, respondents were asked to report the number of calcium pills they took per day (VITYCALCPILS) and the number of milligrams of calcium per pill (VITYCALCMG).

In 2000 and 2005, respondents who had taken calcium during at least one month in the past 12 months were asked how often they had taken calcium in those months (VITACALCNO). Respondents could choose to answer in terms of days per week or days per month (VITACALCTP).

For 2000 (but not 2005), the National Center for Health Statistics recoded data from VITACALCNO and VITACALCTP to create two new variables with consistent time units: number of days per week took calcium during the relevant months of the past 12 months (VITACALCDWK), and number of days per month took calcium during the relevant months of the past 12 months (VITACALCDMO). VITACALCDMO 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 calcium?").

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 VITACALC in 2002 indicates that the sample adult took calcium in high doses. A negative response to VITACALC in 2002 indicates that the respondent did not take high doses of calcium, but does not indicate that he/she took no calcium at all in the past 12 months. By contrast, affirmative responses to VITACALC in 1992, 2000, or 2005 indicate that the respondent took any amount of calcium supplements (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 calcium was 1200 milligrams. Thus, any respondent in 1987 taking more than that amount of calcium in a day would have been considered to be using "high dose or megavitamin therapy" by the above definition offered in the 2002 Field Representative's Manual. (However, by 2002, the Dietary Reference Intake for calcium had been raised to 1300 milligrams per day.)

Researchers who wish to combine data on calcium 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 calcium 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.