Toenail and plasma levels as biomarkers of selenium exposure.

PURPOSE: Both blood and toenail selenium are used to assess selenium exposure in epidemiologic studies. Little is known about the relationship of these biomarkers with each other or about whether there are differences in the relationships of these biomarkers with diet, supplement use, or participant characteristics. METHODS: Data are from 220 participants in a large cohort study of supplement use and cancer risk. Measures of selenium exposure included supplement use (current and 10-year) from a self-administered questionnaire, an inventory of currently used supplements (multivitamins and single supplements), dietary intake from a food frequency questionnaire (FFQ), and selenium concentration in toenails and plasma. RESULTS: Plasma and toenail selenium concentrations were significantly correlated (r=.56 [95% confidence interval: .46, .64]). Supplemental selenium was the strongest predictor of both selenium biomarkers, and these associations were slightly stronger when based on the supplement inventory and 10-year self-reported use compared to current self-reported use. Correlations of current and 10-year questionnaire dose and inventory dose with toenail selenium were .26, .36, and .33; for plasma selenium, these were .27, .36, and .36. Neither dietary selenium nor any participant characteristics, except smoking, was related to either biomarker. Current smokers had lower toenail, but not plasma, selenium levels compared to nonsmokers (.89 versus 1.03 microg/g, p = .03); however, the difference was not significant after control for supplement use (p = .09). CONCLUSIONS: Both toenail and plasma selenium levels similarly reflect selenium intake exposure. There do not appear to be independent associations of toenail or plasma selenium with FFQ-derived selenium intakes, health-related behaviors, or demographic characteristics.

Dietary supplements and weight control in a middle-age population.

OBJECTIVES: Obesity is rapidly becoming a health problem of epidemic proportions, bringing with it a host of health concerns. This study investigates the association of long-term (10-year) use of 14 nutritional supplements, marketed as weight-control aids, with weight change over the past 10 years among individuals age 53 to 57 years. METHODS: Data are from the VITamins And Lifestyle (VITAL) cohort study of western Washington. Participants (n = 15,655) completed questionnaires about 10-year supplement use, diet, health habits, height, and present and former weights. The following supplements that are sometimes marketed for weight control or loss were examined: multivitamins; vitamins B6 and B12; chromium; coenzyme Q10, dehydroepiandrosterone, essential fatty acids (EFAs), fiber, garlic (Allium sativum), ginkgo (Ginkgo biloba), ginseng (Panax spp.), melatonin, soy, and St. John's wort (Hypericum perforatum). Linear regression was used to model 10-year change in weight from age 45 to ages 53-57, stratified by sex and body mass index (BMI, kg/m2) (normal, overweight, or obese) at age 45 years. Models were controlled for race/ethnicity, education, energy intake, physical activity, weight at age 45 years, and smoking. RESULTS: Among overweight or obese men and women, long-term use of multivitamins, vitamins B6 and B12, and chromium were significantly associated with lower levels of weight gain. For example, with chromium, weight gain in the past 10 years for obese men was 11.7 lb for no use, 6.1 lb for <150 microg/day (10-year average), and a weight loss of 3.1 lb for > or = 150 microg/day (p for trend, <0.05). Among obese women, weight gain was 14.1 lb, 7.9 lb, and 3.2 lb for the three groups respectively (p for trend, <0.01). CONCLUSIONS: These data suggest that long-term users of certain supplements experienced less weight gain than individuals who did not use the supplements. Further study is necessary before recommendations regarding these supplements can be made.

Demographic and health-related correlates of herbal and specialty supplement use.

BACKGROUND: By broadening the definition of a dietary supplement, the 1994 Dietary Supplements Health and Education Act opened the market to many herbals, botanicals, and other food ingredients that would have otherwise needed safety testing before being sold. Information regarding patterns and correlates of herbal and specialty supplement use can help nutritionists understand which compounds are most commonly used, who are likely to use these supplements, and whether the choice of herbal supplements appears motivated by specific health concerns. METHODS: Data are from 61,587 participants, aged 50 to 76 years, who completed a self-administered mailed questionnaire in 2000-2002 on current dietary supplement use (20 herbal/specialty supplements, multivitamins, and 17 individual vitamins or minerals), demographic and lifestyle characteristics, and medical history. RESULTS: When compared with no supplement use, herbal/specialty supplement use was significantly higher among respondents who were older, female, educated, had a normal body mass index, were nonsmokers, engaged in exercise, and ate a diet lower in fat and higher in fruits and vegetables (all P<.001). Similar trends were observed when herbal/specialty supplement users were compared with vitamin/mineral users. For specific supplements and medical conditions, the strongest associations were cranberry pills and multiple bladder infections (odds ratio [OR], 4.66; 95% confidence interval [CI], 4.03-5.38), acidophilus pills and lactose intolerance (OR, 3.37; 95% CI, 2.96-3.84), and saw palmetto and enlarged prostate (OR, 3.33; 95% CI, 3.00-3.72). CONCLUSIONS: Odds of supplement use are high for certain demographic and lifestyle characteristics. Additionally, persons with specific medical conditions are using supplements promoted to reduce risk for their particular conditions.

Reliability and validity of self-report of vitamin and mineral supplement use in the vitamins and lifestyle study.

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.

Dietary supplement use and medical conditions: the VITAL study.

BACKGROUND: Over half of U.S. adults use vitamin or mineral supplements, and some are likely using supplements to treat chronic diseases or risk factors for disease. Information on the relationship between supplement use and medical conditions is useful to health professionals to understand the self-medication behavior of their patients, and important for researchers because medical conditions may be potential confounding factors in observational studies of supplement use and disease risk. METHODS: The cross-sectional data in this report are from 45,748 participants, aged 50 to 75 years, who completed a self-administered, mailed questionnaire on current dietary supplement use (multivitamins plus 16 individual vitamins or minerals), medical history (cancer, cardiovascular-related diseases, and other self-reported medical conditions), and demographic characteristics. RESULTS: Supplement use (mean number used at least once a week) was higher among respondents who were older, female, highly educated, Caucasian, and of normal body mass index (all p<0.001). After controlling for these covariates, supplement use was higher among those with the condition for 13 of the 21 conditions examined (p<0.01); only having diabetes or high stress was associated with using fewer supplements. For specific supplements, the strongest associations were for cardiovascular disease and its risk factors with vitamin E, niacin, and folate, and for calcium with indigestion and acid reflux disease. For several conditions, the relative odds of using specific supplements were consistently higher for men than for women. CONCLUSIONS: Supplement use was associated with many medical conditions in this cohort. However, these cross-sectional data do not permit inferences about the temporal sequence. Some associations appeared to be based on evidence for efficacy (e.g., folate with coronary artery disease), and others could be based on misinformation (e.g., selenium with benign prostatic hyperplasia).