Long-term residential sunlight exposure is positively associated with cognitive function in young adulthood and midlife, according to new research from Finland. The findings suggest that sunlight may play a protective role in cognitive health during these stages of life, potentially influencing memory, attention, and other cognitive domains.
Residential sunlight exposure refers to the amount of sunlight that individuals are exposed to in their residential neighborhoods or areas where they live. It takes into account factors such as the location of their residence, the surrounding environment, and the duration and intensity of sunlight in that area.
The new study has been published in Scientific Reports.
Previous studies have shown that sunlight plays a role in cognitive function through its influence on circadian rhythms, sleep patterns, mood, and emotion regulation. Experimental evidence in mice has also suggested that exposure to ultraviolet (UV) radiation, which includes non-visible wavelengths of sunlight, can have beneficial effects on learning and memory.
Observational studies in older populations have indicated a protective association between sunlight exposure and cognitive decline. However, it is not known whether this association exists in younger age groups before the onset of clinical cognitive decline.
To conduct the study, the researchers used data from the Cardiovascular Risk in Young Finns Study, a nationwide prospective cohort study in Finland. They included 1,838 participants who had undergone a comprehensive cognitive assessment in midlife. The participants’ residential history and meteorological data on sunlight were obtained.
The average daily exposure to global solar radiation for different exposure lengths (2 months, 1 year, 2 years, and 5 years) prior to the cognitive assessment date was calculated for each participant’s residential zip code area. The researchers also collected information on individual-level educational attainment and neighborhood-level socioeconomic factors.
Cognitive function was assessed using the Cambridge Neuropsychological Test Automated Battery, which included tests for visual memory, reaction time, visual processing, and short-term working memory. The associations between residential sunlight exposure and cognitive function were analyzed using linear regression models. The analyses were adjusted for factors such as season, sex, age, educational attainment, and neighborhood-level socioeconomic characteristics.
The researchers found that greater average residential exposure to sunlight for exposure lengths of 1 year or longer was associated with better performance in global cognitive function, visual memory and associative learning, and visual processing and sustained attention. The differences in cognitive function between individuals with the highest and lowest sunlight exposure corresponded to a 2- to 4-year difference in cognitive age.
These associations remained statistically significant even after adjusting for individual- and neighborhood-level socioeconomic factors. However, when the researchers looked at shorter time periods, such as 2 months and 1 year before the cognitive function test, they didn’t find any significant associations between sunlight exposure and cognitive function. This suggests that the impact of residential sunlight exposure on overall cognitive function is relatively small, but it can accumulate over time.
The findings provide evidence that long-term sunlight exposure may play a role in cognitive health. However, the study is observational and does not establish causation, and the results may not be generalizable to populations in different geographic locations. The study authors said that further research is needed to understand the mechanisms behind these associations and to explore the relevance of sunlight and other environmental factors in cognitive health at different stages of life.
The study, “Long-term residential sunlight exposure associated with cognitive function among adults residing in Finland“, was authored by Kaisla Komulainen, Christian Hakulinen, Jari Lipsanen, Timo Partonen, Laura Pulkki-Råback, Mika Kähönen, Marianna Virtanen, Reija Ruuhela, Olli Raitakari, Suvi Rovio, and Marko Elovainio.