Effects of Physical Activity on Cognitive Functioning in Middle Age: Evidence From the Whitehall II Prospective Cohort Study

Archana Singh-Manoux, PhD; Melvyn Hillsdon, PhD; Eric Brunner, PhD; Michael Marmot, PhD, MBBS, FFPHM, FRCP

Disclosures

Am J Public Health. 2005;95(12):2252-2258. 

In This Article

Results

The median length of follow-up from phase 1 to phase 5 was 11 years; 355 individuals died during this period. Of the 10308 baseline participants (1985-1988), 8637 provided data at phase 3 (1991-1994), and 7830 provided data at phase 5 (1997-1999). Cognitive functioning and physical activity data at all 3 phases were available for 6236 respondents. In comparison with baseline data, the data used in our analyses were influenced by age (P=.001) and employment grade (P=.001) but not by gender (P=.61). The attrition rate was higher among older respondents and respondents of low socioeconomic position.

Table 1 presents data on respondents' physical activity levels; it can be seen that approximately half of the respondents reported high levels of activity at the 3 phases (51.3% at phase 1, 46.6% at phase 3, and 44.6% at phase 5). Table 1 also shows age- and gender-adjusted data on high, medium, and low levels of physical activity at the 3 phases (phases 1, 3, and 5). Performance on the memory test was not significantly associated (P=.07) with level of physical activity at phase 1. All other F tests were significant. Post hoc tests showed that the low-activity group, but not the medium-activity group, had lower cognitive- functioning scores than the high-activity group at phase 1. At phases 3 and 5, both of these groups had significantly lower mean scores than the high- activity group on all measures of cognitive function. Table 2 shows that 20.7% of the participants reported high levels of physical activity at all 3 phases and that 5.1% reported low levels at all of the phases. Age- and gender-adjusted mean scores differed significantly between the summary levels of physical activity for all of the cognitive tests examined.

Participants reporting a low level of physical activity at baseline (phase 1) were significantly more likely to have cognitive test scores in the lowest quintile after adjustment for age and gender ( Table 3 , model A1). After adjustment for measured covariates and confounders, including Mill Hill Vocabulary Scale score ( Table 3 , model A3), an association remained only between low level of physical activity at baseline and AH 4-I score. Cross-sectional age- and gender-adjusted associations (phase 5 physical activity and phase 5 cognitive functioning) were somewhat stronger ( Table 3 , model B1) than prospective associations (phase 1 activity and phase 5 cognitive functioning). After further adjustment for education, employment grade, self-rated health, blood pressure level, cholesterol level, smoking status, mental health status, and social network index score, low levels of physical activity remained associated with greater risk of poor cognitive functioning for all outcomes examined ( Table 3 , model B2). Additional adjustment for Mill Hill score (as a proxy for baseline cognitive functioning) revealed significant effects of low physical activity levels on AH 4-I score and phonemic fluency ( Table 3 , model B3).

Table 4 presents the odds of being ranked in the lowest quintile of cognitive test scores as a function of summary score (calculated to represent levels of physical activity through the 3 time points). A significant age- and gender-adjusted association was observed between summary score and the odds of being ranked in the lowest quintile on all cognitive tests ( Table 4 , model C1). Tests for linear trend across the summary scale were also significant for all measures of cognitive functioning examined. Adjustment for the covariates assessed ( Table 4 , model C3) significantly attenuated these relationships. The final model, model C3, showed a linear, cumulative dose-response relationship between levels of physical activity across phases 1, 3, and 5 and poor performance on the AH 4-I. A summary score of 6, representing low levels of physical activity at the 3 time points, also was associated with poor phonemic fluency.

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