expert opinion

Where do Americans get their nutrients?

September 15, 2011

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Dr. Johanna Dwyer, Jean Mayer USDA Human Nutrition Research Center on Aging, and the School of Medicine and Friedman School of Nutrition Science and Policy, Tufts University, Boston, USA.

“Most foods contain several naturally occurring nutrients at relatively low levels. The addition of nutrients to foods, either by enrichment (replacing nutrients lost in processing) or fortification (adding nutrients at higher levels than naturally occur in the food), enhances levels of one or more nutrients in certain foods that are widely consumed, thus raising intakes to more desirable levels. In the US, most grain products are enriched and a variety of other food products are fortified. For example, bread is enriched with thiamin, niacin, riboflavin, and iron ; most cereals are fortified with added iron and B vitamins, including folate, and most milk is fortified with vitamin D. In addition to obtaining nutrients from foods, many Americans use nutrient-containing dietary supplements (1). One-half of Americans (aged over 1 year) use dietary supplements, with multivitamin/ mineral supplements being the most common (2).

Unlike in the USA, in Europe fortified staple foods play a comparatively small role in increasing the intake of micronutrients. Even with the inclusion of dietary supplements most children and adults do not exceed the tolerable upper intake level (3). Given that fortification practices and dietary supplement use are very different in the US compared to Europe, this study aimed to determine total usual nutrient intakes for 19 micronutrients from all sources as well as the relative contributions of foods, fortified and enriched foods, and of dietary supplements within a nationally representative sample of the US population from 2 years of age (4).

Study results:

  • The percentage of individuals with total usual nutrient intake, including that from foods and dietary supplements, falling below the estimated average requirement (EAR) was considerable for vitamin D (70%), vitamin E (60%), calcium (38%), vitamin A (34%), vitamin C (25%), and magnesium (45%).
  • In contrast, smaller proportions of the population (< 8%) had total usual intakes below the EAR for
    vitamin B1, B2, B3, B6, B9 and B12, as well as zinc, iron, copper and selenium.
  • Less than 3% of the population had total usual intakes that exceeded the adequate intake (AI) for potassium and about 35% of the population had total usual intake greater than the AI for vitamin K.
  • Enrichment and/or fortification largely contributed to intakes of several micronutrients. Due to intake of fortified/enriched foods, the percentage of the population with usual intakes below the EAR was dramatically reduced compared with usual intakes from only naturally occurring nutrients: 74 to 45% for vitamin A, 51 to 6% for vitamin B1, 88 to 11% for folate, 22 to 7% for iron, 46 to 37% for vitamin C, 22 to 12% for vitamin B6, and 15 to 11% for zinc.
  • The intake of dietary supplements further reduced the percentage of the population consuming less than the EAR for all nutrients, e.g. 45 to 34% for vitamin A, 37 to 25% for vitamin C, 91 to 60% for vitamin E, and 55 to 45% for magnesium.
  • With the addition of intakes from dietary supplements, only small changes in the percentage of the total population exceeding the UL were found: 2–5% for vitamin A, 1–10% for vitamin B3, 1–6% for folate, and 5–8% for zinc.

In conclusion, large percentages of the American population had micronutrient intakes below the EAR. Compared with intakes from naturally occurring nutrients, enrichment and/or fortification significantly improved intakes of several key nutrients. Dietary supplements added to the intakes of those who used them and further reduced the percentage of the population below the EAR.

The percentage of individuals exceeding UL due to intakes from enriched and/or fortified foods and from dietary supplements was relatively small. The proper application of UL values has been the topic of considerable debate. The UL is the highest level of daily intake that is likely to pose no risk of adverse health (5). 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. 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 (6, 7).

Health professionals must be aware of the contribution that enrichment and/or fortification and dietary supplements make to the micronutrient status of Americans. Without enrichment and/or fortification and supplementation, many Americans do not achieve the recommended micronutrient intake levels set forth in the Dietary Reference Intake.”

Boston, August 2011

References

  1. Rock C. L. Multivitamin-multimineral supplements: who uses them? Am J Clin Nutr. 2007; 85:277–279.
  2. Bailey R. L. et al. Dietary supplement use in the United States, 2003–2006. J Nutr. 2011; 141:261–266.
  3. Flynn A. et al. Intake of selected nutrients from foods, from fortification and from supplements in various European countries. Food and Nutrition Research. 2009; Suppl.1:1–51.
  4. Fulgoni III V. L. et al. Foods, Fortificants, and Supplements: Where Do Americans Get Their Nutrients? The Journal of Nutrition. Online publication August 2011.
  5. Food and Nutrition Board, Institute of Medicine. Dietary reference intakes for thiamin, riboflavin, niacin, vitamin B-6, folate, vitamin B-12, pantothenic acid, biotin, and choline. Washington (DC): National Academies Press; 1998.
  6. Renwick A. G. Understanding tolerable upper intake levels: toxicology of micronutrients: adverse effects and uncertainties. J Nutr. 2006; 136:493–501.
  7. Berner L. A. and Levine M. J. Understanding tolerable upper intake levels: overall discussion: gaps and suggestions. J Nutr. 2006; 136:520–521.