Cognitive skills of older adults tend to peak in the late summer and early fall compared to winter and spring seasons, according to researchers at the University of Toronto in Canada.

The study titled "Seasonal plasticity of cognition and related biological measures in adults with and without Alzheimer disease: Analysis of multiple cohorts" was published in PLOS Medicine on Sept. 4.

The research team examined data on 3,353 people with an average age of 77. The participants were recruited for three different cohort studies in the United States, Canada, and France. 

"We tested their thinking and concentration, measured Alzheimer-disease-related proteins in their spinal fluid, performed autopsies on those who died, and measured brain gene expression," they wrote in the paper. 

Confounding factors like mood, sleep, physical activity, and thyroid status were recorded and accounted for.

Overall, it was found the cognitive skills of the participants were found to peak during the late summer and early fall. This was regardless of whether or not they had Alzheimer's disease. When looking at the spring and winter months, the decline in their cognitive function was equivalent to the brain aging by 4.8 years. 

Upon examining the cerebrospinal fluid samples, the team also found seasonal rhythms in their proteins, resulting in an increased expression of dementia-related genes. During the spring and winter periods, the participants were also 30 percent more likely to meet the criteria for being diagnosed with dementia.

"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 added.

But the exact factor driving these changes could not be identified.

Environmental factors like light and temperature were speculated to play a role, especially if warmer temperatures encouraged more social interactions. If so, it may help to use interventions like phototherapy or temperature modification during the months when older adults are more likely to experience dips. 

"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 concluded.

Among limitations, the data only involved people from the temperate northern-hemisphere regions, not from southern-hemisphere or equatorial regions. It was acknowledged each participant was assessed only once per annual cycle.

According to the latest data based in the United States, 5.7 million people of all ages are estimated to be living with Alzheimer's dementia in 2018. Age is considered the most significant risk factor as dementia typically does not affect people who are under the age of 60.

While there is neither a cure nor a sure-fire method to prevent the condition, a healthy lifestyle can help reduce the risk. Among recommendations, experts emphasize the importance of socializing, getting enough physical activity, maintaining a healthy diet, and keeping the brain active.