To examine overall relationships between chronotype, and objective measured physical activity pattern and dementia in older adults, focusing on potential interactions between the chrontype, volume timing of activity and/or sleep and dementia.

Subject were 192 female and 47 male community-dwelling healthy Korean individuals aged 70–85 years. Total volume of activity at an intensity over 3 metabolic equivalents (METs) and timing of activity and sleep pattern were measured by 3 axial accelerometer throughout each 24-h period for 1 month. Participants also completed the morningness-eveningness Questionnaire, which is a 19-item self-report scale with questions focusing on habitual waking and bed times. Partial correlation coefficients adjusted for age and sex were calculated between measurements. We used logistic regression analyses to determine odds ratios and 95% confidence intervals adjusted for potential confounders, and to assess independent associations between chrontype, physical activity pattern and the risk of dementia.

The data were significantly described by partial correlation models, which showed that in both sexes the chrontype score and physical activity associated with cognitive function. Multivariate-adjusted logistic regression analyses predicted who engaged in<12 to 13min/day of moderate-intensity physical activity were, respectively, 2 and 3 times more likely to sustain dementia than those participating in>22min/day of activity>3 METs. Moreover, participants who classified as high in eveningness were 2 times more likely to sustain dementia than those with morningness.

Causation cannot be inferred from a cross-sectional study. Nevertheless, we suggest that from the viewpoint of cognitive health, older population should be encouraged to engage in low- and moderate-intensity habitual physical activity, taking a duration>12 to 13min/day at>3 METs. Moreover, these results suggest that elderly with higher eveningness also have higher risks of dementia.