White blood cell count and psychomotor cognitive performance in the elderly

White blood cell (WBC) count is associated with many inflammatory diseases such as cardiovascular disease, diabetes and hypertension. Research on the relationship of WBC count and cognition in the elderly is relatively sparse. This study examined the association between WBC count and cognitive performance in older adults.

Data from the National Health and Nutrition Examination Survey (1999-2002) containing 1670 older adults were analysed. Every subject completed a household interview, examination of digit symbol substitution test (DSST) scores, WBC count measurement and a questionnaire regarding personal health. WBC count was restricted to the normal range and divided into quartiles, using a multiple hierarchical regression model to estimate the relationship between WBC counts and DSST scores. Quartile-based analysis with an extended-model approach was used for further covariates adjustment. Trends test examining the associations across increasing quartiles of WBC counts and DSST scores were also conducted.

In the multiple hierarchical regression model, the β coefficient, representing the change of DSST scores for each 1000 cells uL(-1) increase in WBC count, was -0·097 (R(2) = 0·343, P < 0·001). After additional competent covariates adjustment, the negative correlation remained (all P < 0·001). In quartile-based multiple linear regression, the negative trends between DSST scores and WBC count quartiles in the stratified comparison with extended-model approach were all statistically significant (P for trends <0·001).

Higher WBC counts, even within the normal range, were associated with poor psychomotor cognitive performance in the elderly.