A new Canadian study finds that most older adults, including those with Alzheimer’s disease, appear to have better cognitive skills in the late summer and early fall than they do in the winter and spring. The difference in cognition is equal to nearly five years of age-related decline.

Very few studies have looked at the association between season and cognition in older adults. In the new work, researchers analyzed data on 3,353 people enrolled in three different cohort studies in the United States, Canada and France.

All of the participants had undergone neuropsychological testing and, in a subset of participants, levels of proteins and genes associated with Alzheimer’s disease were also available.

The researchers, led by Andrew Lim of Sunnybrook Health Sciences Centre and the University of Toronto, found that average cognitive functioning was higher in the summer and fall than the winter and spring, equivalent in cognitive effect to 4.8 years difference in age-related decline.

The findings also show that the odds of meeting the diagnostic criteria for mild cognitive impairment or dementia were higher in the winter and spring than summer or fall. The link between season and cognitive function remained strong even when the data was controlled for potential confounders, including depression, sleep, physical activity and thyroid status.

Finally, an association with seasonality was also seen in levels of Alzheimer’s-related proteins and genes in cerebrospinal fluid and the brain. However, the research was limited by the fact that each participant was only evaluated once per annual cycle, and only included data on individuals from temperate northern-hemisphere regions, not from southern-hemisphere or equatorial regions.

Overall, the study finds that season has a clinically significant association with cognition and its neurobiological correlates in older adults with and without AD pathology.

“There may be value in increasing dementia-related clinical resources in the winter and early spring when symptoms are likely to be most pronounced,” the authors said. “By shedding light on the mechanisms underlying the seasonal improvement in cognition in the summer and early fall, these findings also open the door to new avenues of treatment for Alzheimer’s disease.”

The study is published in the journal PLOS Medicine.

Source: PLOS