Threshold effects and interactive effects of total zinc and selenium intake on cognitive function in older adults

The aim of this study was to assess threshold effects and interactive effects of total zinc and selenium intake on cognitive function in older adults.

We used data from the National Health and Nutrition Examination Survey (NHANES) 2011-2014. Zinc and selenium intake were obtained through two 24-h dietary recalls. Cognitive performance was evaluated by the Digit Symbol Substitution Test (DSST). Smooth curve fitting, two-piecewise multivariable linear regression models, binary logistic regression model, multiplicative interactions model, and additive interactions model were used to evaluate the association between zinc, selenium intake and their interactive effect on cognitive function.

A total of 2450 participants aged 60 years or older were included. Zinc and selenium intake was non-linearly associated with cognitive function. The inflection point for zinc intake was 8.94 mg/d in males and 7.58 mg/d in females. When zinc intake was below inflection point, zinc intake was positively associated with the DSST test in males (β = 1.02, 95% CI, 0.44 to 1.60) and females (β = 0.94, 95% CI, 0.26 to 1.62). When zinc intake above inflection point, there is no association between zinc intake and the DSST test in both sexs. The inflection point for selenium intake was 186.33 μg/d in males and 68.40 μg/d in females. Among males, the β (95% CIs) was 0.03 (0.01,0.06) to the left side of the inflection point and -0.06 (-0.10, -0.02) to the right of the inflection point. Among females, the β (95% CIs) was 0.13 (0.04,0.22) to the left side of the inflection point and 0.01 (-0.01,0.04) to the right of the inflection point. Besides, zinc and selenium have significant interaction on DSST test only in females (P = 0.028, RERI = 0.418).

The present study demonstrated that zinc and selenium intake was non-linearly associated with cognitive function in different sex. There was an interactive effect between zinc and selenium intake on improving cognitive function, especially in females.