Changes in time spent walking and the risk of incident dementia in older Japanese people: The Ohsaki Cohort 2006 Study

Background: the impact of long-term changes in physical activity during adulthood in the context of primary prevention of dementia has not been addressed previously. Objective: to study the relationship between changes in time spent walking after middle age and incident dementia in older Japanese individuals. Methodology: we conducted a cohort study of 6,909 disability-free Japanese individuals aged ≥65 years who lived in Ohsaki City, Japan. In both 1994 and 2006, the individual amount of time spent walking per day was assessed using a selfreported questionnaire ( < 0.5 h, 0.5-1 h or ≥1 h). Based on these three categories of exposure at the two points, participants were categorised into nine groups according to changes in time spent walking. Data on incident dementia were retrieved from the public Long-term Care Insurance (LTCI) Database, in which participants were followed up for 5.7 years (between April 2007 and November 2012). The Cox model was used for estimating the multivariate-adjusted hazard ratios (HRs) of incident dementia. Results: the 5.7-year incidence of dementia was 9.2%. Compared with persons who remained in the lowest category of time spent walking ( < 0.5 h/day in both 1994 and 2006), persons who remained in the highest category (≥1 h/day in both 1994 and 2006) had a significantly lower risk of incident dementia: the multivariate-adjusted HR (95% confidence intervals) was 0.72 (0.53 and 0.97). Conclusions: these results suggest that maintaining a higher level of physical activity after middle age may be a key strategy for prevention of dementia in older age.