Iron and zinc nutrition in the economically-developed world: a review

Abstract

This review compares iron and zinc food sources, dietary intakes, dietary recommendations, nutritional status, bioavailability and interactions, with a focus on adults in economically-developed countries. The main sources of iron and zinc are cereals and meat, with fortificant iron and zinc potentially making an important contribution. Current fortification practices are concerning as there is little regulation or monitoring of intakes. In the countries included in this review, the proportion of individuals with iron intakes below recommendations was similar to the proportion of individuals with suboptimal iron status. Due to a lack of population zinc status information, similar comparisons cannot be made for zinc intakes and status. Significant data indicate that inhibitors of iron absorption include phytate, polyphenols, soy protein and calcium, and enhancers include animal tissue and ascorbic acid. It appears that of these, only phytate and soy protein also inhibit zinc absorption. Most data are derived from single-meal studies, which tend to amplify impacts on iron absorption in contrast to studies that utilize a realistic food matrix. These interactions need to be substantiated by studies that account for whole diets, however in the interim, it may be prudent for those at risk of iron deficiency to maximize absorption by reducing consumption of inhibitors and including enhancers at mealtimes.

Figure 1

Relationship between dietary iron and zinc content of selected foods of plant origin (indicated by black triangles), foods of animal origin (indicated by red circles) (adapted from USDA National Nutrient Database [20]), and fortified breakfast cereals (indicated by green squares [15,16,17,18,19]). For foods of plant origin (black solid line): r = 0.68, P = 0.005. For foods of animal origin (red dash line): r = 0.71, P = 0.001. For fortified breakfast cereals (green dash-dot line): r = 0.87, P = 0.086. Significance does not change when the two outliers, Pacific oysters and US Cheerios^®, are omitted. Values are based on uncooked nuts, carrot, oysters, raisins, oats and dairy products, and plain breakfast cereals; all other foods are cooked.