High iron intake is associated with poor cognition among Chinese old adults and varied by weight status-a 15-y longitudinal study in 4852 adults

Background High body iron status has been shown to be associated with adverse health outcomes. However, the relation between high body iron status, body mass index (BMI), and cognition is still understudied. Objective This study aimed to examine the association between iron intake and cognitive function in Chinese adults and tested the interaction effect of iron intake and BMI on cognition. Design Longitudinal study data from a nationwide sample (n = 4852; age ≥55 y) from the China Health and Nutrition Survey during 1991-2006 were used. Of the participants, 3302 had completed cognitive screening tests in ≥2 surveys. Cognitive function was assessed in 1997, 2000, 2004, and 2006. Dietary iron intake was obtained from a 3-d food record during home visits in 1991, 1993, 1997, 2000, 2004, and 2006. Multivariable mixed linear regression and logistic regression were used. Results The cumulative mean ± SD iron intake in 1997 of tested subjects was 23.7 ± 11.3 mg/d (25.4 mg/d in men and 22.2 mg/d in women). High iron intake was associated with poor cognition. In fully adjusted models, across the quartiles of iron intake the regression coefficients (95% CIs) were 0,-0.39 (-0.77,-0.01),-0.55 (-0.95,-0.15), and-0.90 (-1.33,-0.47), respectively. Comparing extreme quartiles of iron intake (high), the OR (95% CI) for poor cognitive function was 1.30 (1.04, 1.64). There was a significant interaction between iron intake and BMI. The association between high iron intake and poor cognition was stronger among those with a high BMI than those with a low BMI. Among those with a BMI (kg/m 2) >24, across quartiles of iron intake the ORs (95% CIs) for poor cognitive function were 1.00, 1.27 (0.91, 1.78), 1.41 (0.97, 2.04), and 2.04 (1.38, 3.01), respectively. Conclusion Higher iron intake is associated with poor cognition in Chinese adults, especially among those with a high BMI.