Association between metals concentrations and cognitive performance, and effect modification by diet in older U.S. adults

Background: Chronic exposure to metals has been associated with adverse neurological outcomes in the elderly. Although the mechanisms are not completely understood, the inflammatory processes in the brain are suspected as a pathway by which metals exerts their neurotoxicity. In parallel, a high diet quality may protect against chronic inflammation. Objective: We sought to examine the joint associations of overall diet quality - as measured by the Adapted Dietary Inflammatory Index (ADII) and the Healthy Eating Index 2015 (HEI-2015) - and blood metals concentrations on cognitive performance in elderly. Methods: We used data on 1,777 adults aged ≥60 years from the US National Health and Nutrition Examination Survey (NHANES; 2011-2014). We derived the ADII and the HEI-2015 from two nonconsecutive 24-hour diet recalls. Cognitive performance was measured by the Consortium to Establish a Registry for Alzheimer’s disease, the Animal Fluency test, and the Digit Symbol Substitution test. We calculated a composite z-score reflecting the overall cognitive performance. The effect of diet quality and blood metals concentrations on cognitive performances were assessed using generalized linear and additive models adjusted for appropriate confounders. Results: Mean score of overall cognitive performance was 87.8 (SD = 24.3). Higher HEI-2015 scores (reflecting higher diet quality), were associated with higher overall cognitive performance [B= 0.09; 95%CI: 0.02-0.16], while higher ADII scores (reflecting a pro-inflammatory diet) with lower cognitive performance [B= -0.09; 95%CI: -0.17;-0.02]. High lead concentrations were associated with poorer overall cognitive performance. However, this was observed only in subjects with low HEI-2015 or high ADII scores, while there was no association with lead concentrations in subjects with better-quality diets (p-interaction <0.08 for all). Conclusion: Our findings suggest that a better-quality diet, as assessed with a high HEI-2015 or a low ADII score may help prevent blood lead adverse cognitive effects among elderly people.