Some authors have argued that excess micronutrients, specifically zinc, iron, and copper are a cause of a number of diseases, from atherosclerosis to Alzheimer's. (1) But other writers argue that most Americans are micro nutrient-deficient (very few Americans are macronutrient deficient!). (2)
Micronutrients are critical for human health, but many have relatively narrow ranges associated with optimal health. Assuming that U.S. dietary guidelines are valid (debatable, but a good starting point), how many people really are receiving inadequate or overabundant micronutrients?
I searched journal articles featuring contemporary data from the U.S. NHANES which surveys a representative sample of the U.S. population.
Large portions of the population had total usual intakes (food and supplement use) below the estimated average requirement for vitamins A (35%), C (31%), D (74%), and E (67%) as well as calcium (39%) and magnesium (46%). Only 0%, 8%, and 33% of the population had total usual intakes of potassium, choline, and vitamin K above the adequate intake when food and multivitamin use was considered. The percentage of the population with total intakes greater than the tolerable upper intake level (UL) was very low for all nutrients; excess intakes of zinc were the highest (3.5%) across the population of all of the nutrients assessed in NHANES.(3)
Population-based studies indicate that vegetarians have lower mean intakes of vitamin B-12 and zinc and higher intakes of fiber, magnesium, and vitamins A, C, and E than do nonvegetarians. Usual intake data suggest a similar prevalence of inadequacy between vegetarians and nonvegetarians for magnesium and vitamins A, C, and E, with both groups at high risk of inadequate intakes of these nutrients. These same data report that vegetarians have a higher prevalence of inadequacy for iron, vitamin B-12, protein, and zinc than do nonvegetarians. Vegetarians should optimize intakes of vitamin B-12, zinc, and protein; and both vegetarians and nonvegetarians need to increase intakes of calcium, magnesium, fiber, and vitamins A, C, and E. (4)
But these studies only analyze reported food intake, which is notoriously unreliable, even, possibly, in NHANES. Interestingly, NHANES also does actual blood tests, and the results from that research found very few physiologyical (as opposed to dietary) deficiencies. CDC's National Report on Nutritional Indicators (2012, valid for the period 2003-2006, only found deficiencies in B6 (11%), Iron (women: 10%), Vitamin D (8%), Vitamin C (6%). This same report indicates that folate supplementation is responsible for lowering deficiency to less than 1% of the U.S. population. They also note that many women have iodine levels "bordering on insufficiency". They did not note any micronutrient excesses. (5)
(1) Power Foods for the Brain. Barnard, Neil. 2013
(2) see, for example, http://chriskresser.com/are-supplements-really-necessary and http://chriskresser.com/why-you-should-think-twice-about-vegetarian-and-vegan-diets
(3) J Am Coll Nutr. 2014;33(2):94-102. doi: 10.1080/07315724.2013.846806.
Multivitamin/mineral supplement contribution to micronutrient intakes in the United States, 2007-2010.
Wallace TC1, McBurney M, Fulgoni VL 3rd. (Affiliation: Council for Responsible Nutrition)
(4) Am J Clin Nutr. 2014 May 28;100(Supplement 1):365S-368S.
Nutritional adequacy of plant-based diets for weight management: observations from the NHANES.
Farmer B.PlantWise Nutrition Consulting LLC
(5) Second National Report on Biochemical Indicators of DIet and Nutrition in the U.S. Population. 2012