No seasonal influence on cognitive performance in a national sample of older adults in New Zealand

A recent North American study reported seasonal differences in cognitive functioning in older adults. We assessed seasonality of cognitive functioning in a large data set of older adults in New Zealand. Methods The International Residential Assessment Instrument-Home Care (interRAI-HC) data set was analysed using a non-parametric method for testing seasonal distribution of cognitive and depression scale scores. Results Participants were 73 285 New Zealanders 65 years and older who completed their first interRAI-HC assessment (mean age, 81.4 years; 57% female). We analysed this sample cross-tabulating season (summer, autumn, winter and spring) and the Cognitive Performance Scale (CPS) score (Kruskal-Wallis test, P = 0.45). Month-by-month CPS scores also demonstrated no variation (Spearman's test, P = 0.96). There was no association between season of assessment and the Depression Rating Scale score, ruling out variability in affect impacting on cognitive performance (Kruskal-Wallis test, P = 0.99). Conclusion Our findings, limited to the Southern Hemisphere, demonstrate a lack of seasonality in cognitive performance and impairment in older adults.