Reliability and Validity of Self-Report of Vitamin and Mineral Supplement Use in the Vitamins and Lifestyle Study

Abstract

In the United States, dietary supplements contribute a large proportion of micronutrient intakes. Therefore, it is important to collect accurate information on supplement use for studies of micronutrients and disease risk. This report describes the test-retest reliability and validity of a detailed, self-administered mailed questionnaire on vitamin and mineral supplement use. Participants (n = 220) completed the questionnaire at baseline and 3 months later. During an in-person interview, participants provided spot urine and blood samples, and interviewers transcribed nutrient information from their supplement bottle labels. The questionnaire had very good test-retest reliability for mean supplement intake over the past 10 years, with intraclass correlations ranging from 0.69 for beta-carotene to 0.87 for vitamin E. Pearson's correlation coefficients comparing current supplemental intakes from the questionnaire and interviews/label transcriptions were high, ranging from 0.58 for beta-carotene to 0.82 for chromium; however, for some nutrients, median intakes from the questionnaire were slightly lower than from the interviews. Beta-carotene, vitamin C, and vitamin E (alpha-tocopherol) showed clear linear trends of increasing blood concentrations with higher self-reported supplemental intakes (Pearson's correlation coefficients adjusted for potential confounding factors and diet = 0.31, 0.29, and 0.69, respectively; all p < 0.0001). Creatinine-adjusted spot urinary calcium values were not associated with supplemental calcium intakes (Pearson's r = -0.07). This self-administered questionnaire demonstrated high reproducibility and validity for collecting detailed information on supplement use.

Associations of Antioxidant Nutrients and Oxidative DNA Damage in Healthy African-American and White Adults

“…Next, they reported whether they took a single nutrient supplement of h-carotene, vitamin A, vitamin C, or vitamin E, and if yes, the frequency and usual dose (amount per day). Daily intake of each nutrient was calculated as follows: frequency (days per week) Â dose per day / 7 (days) (30). For these analyses, participants are categorized as ''nonusers'' or ''users'' of dietary supplements from this instrument.…”

“…This open-ended approach is more valid than selfadministered questionnaires (30). Average daily nutrient intake from the inventory was calculated as follows: frequency (days per week)  number of pills taken each time  dose per pill / 7 (30).…”

“…This open-ended approach is more valid than selfadministered questionnaires (30). Average daily nutrient intake from the inventory was calculated as follows: frequency (days per week)  number of pills taken each time  dose per pill / 7 (30). We then summed intakes of each individual nutrient from all multivitamins and single supplements reported to determine a total average daily intake for each nutrient.…”

Dietary Supplement Use by Community-living Population in Japan: Data from the National Institute for Longevity Sciences Longitudinal Study of Aging (NILS-LSA)

“…At present, there have been a few studies on dietary supplement assessment methodology. [5][6][7]11,21,[24][25][26][27] It is important to develop generally accepted assessment method in the dietary supplement study to make direct comparison.…”

Use of dietary supplements among US adults with asthma

“…This method has been used as the reference method to assess the validity of self-reported dietary supplement use in other studies. 31,32 The definition of asthma was based on self-report, which is subject to recall bias and misclassification. However, it is not feasible for large epidemiological studies such as NHANES to validate all self-reported medical histories.…”