Abstract
Iron and zinc are found in similar foods and absorption of both may be affected by food compounds, thus biochemical iron and zinc status may be related. This cross-sectional study aimed to: (1) describe dietary intakes and biochemical status of iron and zinc; (2) investigate associations between dietary iron and zinc intakes; and (3) investigate associations between biochemical iron and zinc status in a sample of premenopausal women aged 18–50 years who were recruited in Melbourne and Sydney, Australia. Usual dietary intakes were assessed using a 154-item food frequency questionnaire (n = 379). Iron status was assessed using serum ferritin and hemoglobin, zinc status using serum zinc (standardized to 08:00 collection), and presence of infection/inflammation using C-reactive protein (n = 326). Associations were explored using multiple regression and logistic regression. Mean (SD) iron and zinc intakes were 10.5 (3.5) mg/day and 9.3 (3.8) mg/day, respectively. Median (interquartile range) serum ferritin was 22 (12–38) μg/L and mean serum zinc concentrations (SD) were 12.6 (1.7) μmol/L in fasting samples and 11.8 (2.0) μmol/L in nonfasting samples. For each 1 mg/day increase in dietary iron intake, zinc intake increased by 0.4 mg/day. Each 1 μmol/L increase in serum zinc corresponded to a 6% increase in serum ferritin, however women with low serum zinc concentration (AM fasting < 10.7 μmol/L; AM nonfasting < 10.1 μmol/L) were not at increased risk of depleted iron stores (serum ferritin <15 μg/L; p = 0.340). Positive associations were observed between dietary iron and zinc intakes, and between iron and zinc status, however interpreting serum ferritin concentrations was not a useful proxy for estimating the likelihood of low serum zinc concentrations and women with depleted iron stores were not at increased risk of impaired zinc status in this cohort.
Highlights
The 2011–2012 Australian Health Survey indicated that 12% of women 16–44 years of age had depleted iron stores compared to 1%–2% of Australian men [2].Premenopausal women with iron stores at this level are more likely to experience impaired physical performance [3], and there is some evidence that cognitive ability may be negatively affected [4,5].As iron is found in similar food sources to zinc [6,7], inadequate dietary iron and zinc intakes may occur simultaneously [8]
Compounds such as phytate may further impede absorption of both iron and zinc from foods [9,10]. Due to these diet-based similarities, there is potential for iron and zinc status to be positively correlated [14,15,16,17], there are no data on zinc status to explore this relationship in Australian women
This finding is in line with previous research that reported a positive association [14,16,17], in our cohort, women with biomarkers below internationally-recognized cut-offs for low levels of one mineral were not more likely to present with low levels of the other mineral
Summary
The 2011–2012 Australian Health Survey indicated that 12% of women 16–44 years of age had depleted iron stores (serum ferritin < 15 μg/L [1]) compared to 1%–2% of Australian men [2].Premenopausal women with iron stores at this level are more likely to experience impaired physical performance [3], and there is some evidence that cognitive ability may be negatively affected [4,5].As iron is found in similar food sources to zinc [6,7], inadequate dietary iron and zinc intakes may occur simultaneously [8]. It is widely acknowledged that the inorganic form of iron, non-heme iron, is less bioavailable than heme iron [11], and it has been hypothesized that analogous to non-heme iron, inorganic zinc salts in plants are a less bioavailable form of dietary zinc [12,13]. Compounds such as phytate may further impede absorption of both iron and zinc from foods [9,10]. Assessment of zinc status is notoriously difficult [18], as zinc plays a crucial role in immune function [19]
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