•What is the primary question addressed by this study?•Is dietary copper (Cu) intake associated with cognitive decline in the elderly?•What is the main finding of this study?•Analysis in this cohort of 3,106 participants found that there was a nonlinear inverse association of dietary Cu intake with cognitive decline in the elderly, with an inflection point at approximately 1.3 mg/day of dietary Cu. The inverse association between dietary Cu and cognitive decline was stronger in those with lower dietary fat intake and lower levels of physical activity (All p-interactions <0.05).•What is the meaning of the finding?•Our study underscores the importance to maintain optimal dietary Cu levels to prevent cognitive decline in the elderly.