Plasma trace elements and cognitive function in older men and women: the Rancho Bernardo study

This study examines the sex-specific associations of plasma concentrations of iron, copper, and zinc with cognitive function in older community-dwelling adults.

Cross-sectional study.

1988-92 follow-up clinic visit.

602 men and 849 women (average age=75 +/- 8 years) who were community-dwelling and not clinically demented.

Blood samples were assayed for trace elements and 12 cognitive function tests were administered. Sex-specific analyses were adjusted for age, education, alcohol consumption, smoking, exercise, and estrogen use in women.

Men and women differed significantly in education and alcohol intake (p's < 0.001), concentrations of plasma iron, copper and zinc (p's < 0.001) and scores on 11 of 12 cognitive function tests (p=0.04 to < 0.001). Regression analyses showed significant inverted U-shaped associations in men; both low and high iron levels were associated with poor performance on total and long-term recall and Serial 7's (p's=0.018, 0.042 and 0.004, respectively) compared to intermediate concentrations. In women, iron and copper concentrations had inverse linear associations with Buschke total, long and short-term recall and Blessed scores (p's < 0.05). Zinc was positively associated with performance on Blessed Items (p=0.008). Analyses comparing cognitive function using categorically defined mineral concentrations yielded similar sex specific results.

Optimal trace element concentrations may exist for optimal cognitive function in older adults, and these levels may differ by sex and cognitive function domain.