Seasons — by their very nature — bring change, be it in air temperature, the amount of daylight or the plants that are in bloom.

These changes also affect humans, albeit in ways we're only starting to understand. Take, for example, how the seasons affect our sense of cognition and what that means for those with Alzheimer's.

A study published in PLOS Medicine investigated that question and found that cognition in seniors improves during summer and autumn and goes into a comparative spiral in winter and spring in the Northern Hemisphere. These findings may influence when we test for and how we treat Alzheimer's.

Seasonal cycles of cognition

Researchers collected data from 3,353 participants from three observational community studies and two observational memory clinic studies spread across the United States, Canada and France. Additionally, participants were put through neuropsychological testing, and a subset of study participants had their cerebrospinal fluid checked for Alzheimer's disease biomarkers. Other tests were performed on study participants who died during the study to collect information about the dorsolateral prefrontal cortex, a section of the brain that helps regulate executive functions, like memory, planning and cognition.

Even after accounting for factors like sleep, depression and physical activity, the research demonstrated a "significant and reproducible association between season and cognition," with the peak occurring near the fall equinox. Participants showed an almost 30 percent higher chance of meeting the criteria for mild cognitive impairment (MCI) and dementia during winter and spring than they did during summer and fall. This association carried over in participants already diagnosed with Alzheimer's, and the difference in when participants were tested could amount to a four-year age difference in cognition.

Senior woman looks out the window during winter Cognition among seniors faltered during winter and spring months. (Photo: Suzana Marinkovic/Shutterstock)

The findings represent a potential new way of thinking about how and when we test for Alzheimer's and how we treat it over the course of the year. For instance, given that even among those already diagnosed with Alzheimer's experienced an increase in cognition during the fall, it may be possible to leverage the increased cognitive functions year-round with appropriate care and treatment. Additionally, testing for MCI and dementia may be more helpful during winter and spring months, when cognition is in decline, to get a clearer sense of its severity.

Currently, it's unclear how and why the seasons play a role in cognition. Researchers speculate that light and temperature, changes in hormone levels or access to vitamin D may all exert some level of influence on cognition. If it's some kind of biochemical response, replicating it somehow could lead to a year-round increase in cognition.

Researchers note that the study participants were all from the Northern Hemisphere, and that it would be worthwhile to conduct similar studies in the Southern Hemisphere, where the seasons and their effects may function in an opposite fashion.

Our brain power changes with the seasons
A PLOS Medicine study has found that cognition in older adults is influenced by the seasons.