Current dietary guidance recommends that individuals achieve recommended nutrient intakes from food sources while not exceeding their energy requirements (1
). Although all foods contain some naturally occurring nutrients, naturally nutrient-dense foods such as fruits and vegetables, whole grains, milk, and lean meats are more likely to help individuals meet their nutrient needs. Other foods contain both naturally occurring nutrients and nutrients added through fortification and/or enrichment. In evaluating total usual intake, most Americans met their recommended nutrient target for the majority of vitamins and minerals evaluated; however, far fewer individuals would have done so without fortification and enrichment. Nevertheless, even after accounting for the contributions of fortification and/or enrichment and dietary supplements, considerable percentages of individuals aged ≥2 y had intakes that were below the EAR for calcium and vitamin D and very few consumed the recommended amount of potassium (all nutrients that the 2010 Dietary Guidelines for Americans
singled out as being of public health concern). Intakes of magnesium and vitamins A, C, E, and K were also low for a considerable percentage of the population. Our data suggest that enrichment/fortification makes a greater contribution in the U.S. compared to Europe. Flynn et al. (14
) reported that nutrients naturally occurring in foods were the major source of nutrients in most European countries. This may be because the U.S. fortifies and enriches foods to a greater extent than most European countries.
In addition to a sizeable percentage of the population who appeared to have intakes below recommended levels for some micronutrients, children were also likely to exceed the UL for certain vitamins and minerals. Children were also more likely to exceed the UL in Europe as well, with retinol, zinc, and magnesium specifically mentioned (14
). However, the proper application of UL values for children has been the topic of considerable debate (30
). The UL is the highest level of daily intake that is likely to pose no risk of adverse health (24
). As intake increases above the UL, the risk of adverse effects may increase. However, the UL is based on a risk assessment approach and it is not recommended to be used as a rigid standard or cutoff point; other factors must be considered to assess any possible adverse health effects of intakes exceeding UL values (24
). More research is needed on the adverse health effects, if any, from intake levels exceeding the UL, especially because the UL for children for several nutrients, including folate, zinc, and vitamin A, were based on data with considerable limitations, including insufficient dose-response and toxicity data (31
The separation of added nutrients allowed for correct assessment of certain nutrient intakes above the UL, namely magnesium and niacin, which without doing so would overestimate the percentage of the population with intakes greater than the UL. In our data, using total niacin intake for UL purposes (not eliminating the naturally occurring niacin), the estimate of the population that exceeds the UL was ~50% as compared to 10% when conducted with only added niacin intakes.
A major strength of our study is the use of a large nationally representative population-based sample of children and adults to assess the source of total usual intake of nutrients with the National Cancer Institute method. For the first time, to our knowledge, intakes of micronutrients naturally occurring in foods and intakes of nutrients contributed by enrichment and/or fortification were separately determined. One of the limitations to our study was that both dietary intake and dietary supplement intake estimates were self-reported and as such were subject to bias. Additionally, our estimates of naturally occurring nutrients and nutrients added to foods were approximate given the assumptions needed to determine these intakes.
In conclusion, most Americans met their needs for many of the micronutrients examined. However, large percentages of the population had intakes below the EAR for magnesium and vitamins A, C, D, and E, and very few individuals obtained the recommended level of potassium. Compared with intakes from naturally occurring nutrients, enrichment and/or fortification dramatically improved intakes of several key nutrients, including folate, thiamin, iron, and vitamins A and D. Dietary supplements added to the intakes of those who used them and further reduced the percentage of the population below the EAR for magnesium and vitamins A, C, and E. Intakes from enrichment and/or fortification and from dietary supplements also increased the percentage of participants whose intakes exceeded the UL for niacin, vitamin A, folate, and zinc. The percentage of individuals exceeding UL for most nutrients was relatively small. Health professionals must be aware of the contribution that enrichment and/or fortification and dietary supplements make to the nutritional status of Americans.