Dietary Intake Levels of Iron, Copper, Zinc, and Manganese in Relation to Cognitive Function: A Cross-Sectional Study

Abstract

Background: Previous studies have related circulating levels of trace metal elements, of which dietary intake is the major source, to cognitive outcomes. However, there are still relatively few studies evaluating the associations of dietary intake levels of iron, copper, zinc, and manganese with cognitive function (CF). Methods: We leveraged the data of 6863 participants (mean [standard deviation] age = 66.7 [10.5] years) in the Health and Retirement Study (2013/2014). Dietary intake levels of iron, copper, zinc, and manganese were calculated from a semi-quantitative food frequency questionnaire. CF was assessed using the 27-point modified Telephone Interview for Cognitive Status (TICS). We used linear regression models to calculate the mean differences in global CF scores by quintiles of dietary intake levels of trace metal elements. Results: Among the study participants, the mean (SD) values of daily dietary intake were 13.3 (6.3) mg for iron, 1.4 (0.7) mg for copper, 10.7 (4.6) mg for zinc, and 3.3 (1.6) mg for manganese. Compared with the lowest quintile of dietary iron intake (<8.1 mg), the highest quintile (≥17.7 mg) was associated with a lower cognitive score (-0.50, -0.94 to -0.06, P-trend = 0.007). Higher dietary copper was significantly associated with poorer CF (P-trend = 0.002), and the mean difference in cognitive score between extreme quintiles (≥1.8 vs. <0.8 mg) was -0.52 (95% confidence interval: -0.94 to -0.10) points. We did not observe significant associations for dietary intake of zinc (P-trend = 0.785) and manganese (P-trend = 0.368). Conclusion: In this cross-sectional study, higher dietary intake of iron and copper was related to worse CF, but zinc and manganese intake levels were not significantly associated with CF.

Keywords: cognitive function; cross-sectional study; diet; trace metal.

Figure 1

Restricted cubic splines for the association of dietary intake levels of iron, copper, zinc, and manganese with global cognitive score. The reference point was set as the median values of dietary intake levels of iron, copper, zinc, and manganese. P-nonlinear = 0.209 for dietary iron intake, 0.836 for dietary copper intake, 0.613 for dietary zinc intake, and 0.704 for dietary manganese intake. The solid line represents the beta of the linear model, and the shaded area represents the 95% CIs of beta.

Figure 2

Restricted cubic splines for the association of dietary intake levels of iron, copper, zinc, and manganese with global cognitive score by age, sex, and cardiometabolic disease. The solid line represents the beta of the linear model, and the shaded area represents the 95% CIs of beta.