Bidirectional associations of Physical Activity and Cognitive Function in Midlife Adults: A Longitudinal Analysis across 26 years follow-up.

Prior studies linking physical activity (PA) and cognition typically assume a causal association between PA and subsequent cognition. Yet, there remains speculation regarding the direction of this association. We investigated bidirectional associations between PA and cognition. Participants of the Medical Research Council National Survey of Health and Development cohort, all born in 1946 reported their PA frequency, undertook processing speed and word recall memory tasks throughout midlife (ages 43 years(y), 53y, 63y and 69y). There was evidence of bidirectional associations in initial structural equation models. To quantify this relationship, mixed-effects models were fitted with a lagged predictor and controlling for childhood cognition, socioeconomic and health factors, attrition and mortality. Among 2,888 participants (51% female) we report bidirectional associations between cognition and PA in midlife. A 1-standard deviation increase in verbal memory was associated with an increased probability of being in the mid-active category at the subsequent wave for females (Relative Risk Ratio (RRR):1.30 (95% Confidence Interval (CI):1.15-1.46)), while becoming active was associated with a minimally greater subsequent verbal memory z-score (β= 0.08, 95%CI: 0.01-0.14). Bidirectional associations proved more robust for males. Results suggest that reciprocal associations exist between PA and cognition, yet stronger in the direction of cognition to PA.