Assessing Total Nutrient Exposures from All Sources in U.S. Adults

Dietary supplement (DS) use in the United States is pervasive, with approximately half of U.S. adults currently taking a DS. Although no consensus exists as to whether DS are beneficial to the prevention of chronic disease, strong scientific evidence supports sufficient nutrient intakes for optimal health. The Dietary Guidelines for Americans recommend that nutrient needs be met primarily through nutrient dense foods; however, it is recognized that in certain cases, dietary supplements and fortified foods may be necessary in order to meet nutrient needs. Currently, little is known regarding whether inclusion of DS can improve micronutrient intakes of some U.S. population subgroups, and how DS use patterns relate to income indicators among U.S. adults. Since DS contain nutrients in amounts as high as the National Academies for Science, Engineering, and Mathematics’ Dietary Reference Intakes, failing to evaluate the contributions of DS to total nutrient intakes when assessing the nutritional adequacy of the U.S. population may lead to inaccurate findings. Therefore, the overarching aims of the research presented in this thesis were to 1) provide updated estimates of DS use, 2) to examine the relationship between DS use and demographic, socioeconomic, and health-related characteristics, and 3) to examine the contributions of DS to total usual micronutrient intakes relative to the DRIs for adequacy (i.e., the EAR or AI) and excess (i.e., the UL) among U.S. adults by sex, age, race/Hispanic origin, and income, using data from the NHANES, 2011-2014.

The thesis begins with a narrative review evaluating the body of evidence investigating the best practices for dietary supplement assessment and total nutrient exposures. Collectively, little is known about the measurement error structure of DS reporting, and currently no standardized methods are available to assess the prevalence of use and nutrient exposures from DS. Chapters 2 and 3 are comprised of two cross-sectional studies using data from the National Health and Nutrition Examination Survey (NHANES) with regard to DS usage patterns and previous related literature relative to the research aims, the contribution of dietary supplements to total micronutrient intakes, and the prevalence of DS use by demographic, socioeconomic and health-related characteristics among U.S. adults.

The evaluation of the prevalence of dietary supplement use by socioeconomic and health-related characteristics indicates that one or more DS are used by over half of U.S. adults (52%), particularly multivitamin-mineral DS, and income is associated with DS use, type, and number of supplements taken. This study provided additional information on DS use in relationship to family income, food security, and SNAP participation status. To our knowledge, this study is the first to use NHANES data to provide information assessing the relationship between DS use and various indicators of participants’ economic status among U.S. adults, including food security.

The study that evaluated the contribution of dietary supplements to total micronutrient intakes among U.S. adults by a number of demographic characteristics, and suggests that the use of micronutrient-containing DS substantially contributed to total nutrient intakes and reduced the risk of inadequacy for several micronutrients across all sex, age, race, and income groups in the U.S. population. However, many U.S. adults still have inadequate intakes of potassium, magnesium, calcium, vitamin D, vitamin A, and/or vitamin C and these population subgroups at risk for inadequacy differ by sex, age, and race/Hispanic origin, and income. Use of DS substantially reduced the prevalence of inadequate intakes for calcium and vitamins D and C, but not for the other 17 micronutrients assessed. DS use also increased the risk of potentially excessive intakes, especially among DS users.

Collectively, the findings from the studies presented in this thesis contribute additional, updated evidence on the use of DS and their contributions to total nutrient exposures in different subpopulations of U.S. adults. Our outcomes point to a need for further investigation into how DS contribute to nutrient exposures and nutrient disparities present in certain subgroups of the U.S. adult population, as well as a standardization of methods to assess the prevalence of use and nutrient exposures from DS.