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Do you find that the time of year affects how well you are able to think? While studies have found this to be the case with young adults, there are few studies that look at the effects on thinking according to different seasons in older adults with and without dementia. 

Although there is no formal definition of what constitutes an “older adult”, according to most developed countries, an older person is defined as a person 65 years of age or older. The United Nations puts the number back a few years to age 60.

As summer winds down and we head into fall, a new study published in the PLOS Medicine has found that the cognitive function of older adults is actually better during this time of the year.

“We asked the question whether older adults’ thinking, memory, and concentration would change at different times of the year,” study author Andrew S. Lim told us. “And if so, what brain changes were responsible for this.”

Lim is an assistant professor and clinician scientist in the Division of Neurology, in the Department of Medicine at Sunnybrook Health Sciences Centre at the University of Toronto in Ontario, Canada. Based on previous studies, Lim and colleagues hypothesized that cognitive abilities would change based on the changing seasons.

“It was well established that thinking, memory, and concentration can vary with circadian (daily) rhythms,” Lim told us. “Also, we had published a previous study showing that many genes in the brain show seasonal rhythmicity.”

More than three thousand older adults from Toronto, Paris, and Chicago participated in the study. Thinking, memory, and concentration and how they varied with season were measured. Researchers also looked at the levels of Alzheimer’s disease-related proteins in the cerebrospinal fluid, and the expression of key genes in the brain.

“We found that on average, individuals evaluated in the late summer and early fall had better thinking, memory, and concentration that those evaluated in the late winter and early spring, with a difference equivalent to over 4 years of aging,” Lim told us. “As well, those evaluated in the late winter and early spring had a nearly 30 per cent higher odds of being diagnosed with mild cognitive impairment or dementia. This was paralleled by seasonal rhythms in Alzheimer’s disease-related proteins and in brain gene expression.”

Data was derived from the Sunnybrook Dementia Study, the Rush Memory and Aging Project, the Minority Aging Research Study, the Religious Orders Study, and the Centre de Neurologie Cognitive study. Neuropsychological testing was conducted and researchers examined RNA sequencing and the AD biomarkers of cerebrospinal fluid.

Lim and his colleagues expected that season would have some effect, but they were surprised at the magnitude of the effect and believe there is much to do as a result going forward.

“Some fraction of patients diagnosed with mild cognitive impairment (MCI) or dementia in the late winter and early spring may show spontaneous improvement and may no longer meet criteria for MCI or dementia by fall,” Lim told us. “Resources devoted to dementia care and diagnosis may need to be increased in the late winter and early spring when the clinical need is anticipated to be greatest.”

Lim explained to us that even patients with established Alzheimer's disease pathology retain some degree of cognitive plasticity, which may potentially be harnessed to improve cognitive function and that as we gain a better understanding of the environmental (e.g. light, temperature), behavioural (e.g. physical activity, diet), physiological (e.g. sex hormones, vitamins like vitamin D), and molecular (e.g. genes) factors driving seasonal rhythms of cognition, we may be able to design environmental, behavioural, physiological, or pharmacological interventions to harness the residual cognitive plasticity in patients in Alzheimer's disease.