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Nutrition

Multivitamins Overview

Cardiovascular Disease  |  Type 2 Diabetes  |  HIV+  |  Hypertension  |  Weight Loss and Maintenance


Introduction

To compensate for perceived dietary deficiencies or promote optimal health, many Americans (52% of adults) take dietary supplements.  According to the latest NHANES survey, multivitamins, typically formulated at about 100% Daily Value (DV) for most vitamins and selected minerals, are the most commonly used supplement (35% of adults) [1].

Multivitamin use increases with age, education, income and, with the exception of pregnant and lactating females, is most prevalent among non-Hispanic white men and women ³ 60 y.  Users are also more likely to have a normal BMI, engage in regular physical, and be nonsmokers [2].  Surveys indicate that, in general, groups less likely to use dietary supplements, including multivitamins, have a higher prevalence of nutrient deficiencies or low nutrient status.

Data from the NHANES III and 1999-2000 surveys indicate that total mean intakes of vitamins A, C, E, K, B6, B12, thiamin, riboflavin, niacin, and folate and the minerals copper, iron, zinc, magnesium, and selenium from food plus supplements were higher than the levels achieved with food alone.  In most cases, the percentage of U.S. adults consuming a diet below the RDA for these micronutrients was lower when total intakes from food and supplement sources combined were considered. 

Research

Few randomized trials have examined the health benefits of multivitamin use among nonpregnant adults.  Well designed studies must take into account multivitamin dose, formulation, duration of use, subjects’ health and usual diet as well as physiologically relevant biomarkers. 

Observational studies indicate that multivitamin use is associated with a reduced risk of cataracts [3], certain cancers [4,5], and coronary heart disease [6]. Clinical trials have demonstrated the beneficial effects of multivitamins on nutrient status [7], immune response [8, 9]. hypertension [10], fertility [11], and HIV progression [12]. 

Guidelines and Recommendations

Guidelines from some professional societies or government panels recommend obtaining vitamins and minerals from food sources rather than supplements, however, the evidence to date regarding the use of multivitamins in preventing micronutrient deficiencies (both overt and sub clinical) and related diseases has prompted their recommendation in certain cases.  According to the U.S. Preventive Services Task Force recommendations on routine vitamin supplementation to prevent cardiovascular disease and cancer, there is insufficient evidence to recommend for or against the use of multivitamins, yet there is little reason to discourage people from taking them. Patients should be reminded that taking multivitamin supplements does not replace the need to eat a healthy diet.

Recently, arguments supporting the use of a single daily multivitamin have appeared in the literature [13-15].  Fletcher and Fairchild [14, 15] justify this practice by citing the known and suspected benefits of supplemental folate, vitamins B6, B12, and D in preventing CVD, cancer, and osteoporosis.  According to Willett and Stampfer [13] a multivitamin will ensure an adequate intake of other vitamins for which the evidence of benefit is indirect.  When formulated at doses about 100% DV, multivitamins are inexpensive, safe, and appear to confer a greater likelihood of benefit than harm.

Critical Thinking Questions:

  1. What is the definition of a multivitamin?  Is this definition consistent between studies?
  2. Can multivitamins effectively compensate for low or suboptimal dietary intake and/or reduced absorption of key micronutrients?
  3. Can multivitamins prevent or significantly reduce the risk for developing chronic disease?
  4. Who might need to be cautious about the amounts of vitamin A, K, or iron contained in a multivitamin supplement?
  5. Why can’t a multivitamin supplement substitute for a healthy, balanced diet?
  6. Should a multivitamin supplement be recommended to all adults patients?
  7. How might you assess the quality of a multivitamin product?

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TUFTS UNIVERSITY PROGRAM IN EVIDENCE-BASED COMPLEMENTARY AND ALTERNATIVE MEDICINE
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Acknowledgements and disclaimer | Date last modified: Wednesday, February 08, 2006

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