Memory and concentration peak in the late summer for adults in their 70s, 80s, and 90s according to a new study co-led by Columbia neurologist Philip De Jager, MD, PhD. The findings suggest that cognitive function in older adults varies over the course of the year as the seasons change, even among those who have Alzheimer’s disease.
Further research to understand the mechanism by which these seasonal changes occur may lead to new ways to treat memory loss and improve cognitive performance in patients with Alzheimer’s disease.
Why do this study?
“We had previously discovered that the change in seasons causes large-scale alterations in the nucleus and function of brain cells in older individuals,” says De Jager, who is the Weil-Granat Professor of Neurology at Columbia University Vagelos College of Physicians and Surgeons.
“We hypothesized that, if brain cell function was changing so much, cognitive function, which is the expression of brain cell function, might also be affected by seasonal rhythms.”
How was the study conducted?
The study looked at more than 3,300 older adults from multiple ethnic groups living in the United States, Canada, and France.
An older person functioned as if they were four years older in the winter, compared to the summer.
Participants had annual evaluations that included 19 different cognitive tests—measuring, for example, working memory, perceptual speed, and visuospatial ability. The scores were averaged to create a composite cognitive score.
The researchers also looked for seasonal variations in gene activity and in diagnoses of mild cognitive impairment (MCI), Alzheimer’s, and dementia.
What did the study find?
Among older adults, cognitive performance peaked just before the fall equinox (this year, Sept. 22 in the Northern Hemisphere) and reached a low point near the spring equinox. The effect was strongest for working memory and perceptual speed.
“The seasonal difference is significant,” says De Jager. “Cognitive function normally declines with age, and the seasonal difference we found is roughly equivalent to four years of aging. This means that an older person functioned as if they were four years older in the winter, compared to how they functioned in the summer.”
The fluctuations were seen in both healthy adults and adults diagnosed with Alzheimer’s, though seasonal differences were smaller in those with dementia.
The effect did not change when other factors that can influence cognitive function were considered. These included symptoms of depression, self-reported hours of sleep and physical activity, and thyroid activity (measured by hormone levels).
What does the study mean?
The presence of robust seasonal variation in cognition among people with Alzheimer’s suggests that identifying the underlying mechanisms could lead to new ways to improve cognitive performance in dementia patients and in people at risk of cognitive decline.
The findings also suggest that Alzheimer’s patients may need more care in the winter and early spring than in the summer.
Identifying the underlying mechanisms could lead to new ways to improve cognitive performance in dementia patients and in people at risk of cognitive decline.
Seasonal changes in cognition may account for the observation that some individuals diagnosed with MCI can regain normal cognition when they are re-evaluated at a later date.
The study did not examine younger adults, but previous studies have not found any association between season and cognition. “We think that an abundance of cognitive reserve in younger adults may account for the age difference,” De Jager says.
This strong seasonal effect needs to be confirmed by larger studies, De Jager says.
In parallel, the researchers are looking for the molecules in the brain that are driving this seasonal effect, so that drugs could be developed to mimic the effect of improved cognitive performance in the summer. Exposure to light is another possible approach to modulate these changes in brain function, and, if true, phototherapy may be effective at maintaining peak cognition year-round.
Each participant was evaluated only once per year; repeated testing of the same individual throughout the year will provide a more accurate and person-specific measure of the extent to which brain and cognitive function changes with the seasons.
Objective measures of sleep and physical activity also may help to refine observations by accounting for other important variables that can change with the seasons and affect brain function.
Philip De Jager is also director of the Center for Translational and Computational Neuroimmunology in the Department of Neurology at Columbia University Vagelos College of Physicians and Surgeons and director of the Multiple Sclerosis Clinical Care and Research Center at Columbia University Irving Medical Center.
Co-senior author Andrew S.P. Lim is an assistant professor in the Department of Medicine at the University of Toronto and an attending neurologist at Sunnybrook Health Sciences Centre.
The study, “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, 2018.
Some authors of the paper are consultants for pharmaceutical companies and receive grants for continuing medical education activities. See paper for full details and a full list of authors.
The study was supported by the National Institutes of Health (grants P30AG10161, R01AG052488, R01AG043379, R01AG15819, R01AG17917, R01AG36042, R01AG36836, U01AG046152, RF1AG022018, R01AG042210, and R01NS078009); Canadian Institutes of Health Research (MOP125934, and MSH136642); Alzheimer’s Association; Brain Canada (AARG501466); National Sciences and Engineering Research Council of Canada (RGPIN-2017-0692); Agence Nationale de la Recherche (MALZ grant 2013); Agence Publique Hopitaux de Paris; Institut National de la Sante et de la Recherche Medicale; Illinois Department of Public Health; Alzheimer Society of Canada; Heart and Stroke Foundation of Canada; and the Robert C. Borwell Endowment Fund.