Researchers out of the University of Alabama Birmingham recently report that lack of sun exposure may lead to cognitive decline over time.
The study, led by Dr Shia T Kent and published in International Journal of Biometeorology, sought to determine if sunlight and air temperature play a role in cognitive decline.
Sun exposure has profound effects on human physiology, with stimulation of vitamin D production being one of its main effects. Lately, vitamin D’s effect on the brain has received more and more appreciation. Vitamin D receptors are located throughout the brain. Vitamin D may be “neuroprotective” and have wide beneficial influence on mental health.
In this study, the researchers studied participants enrolled in the REGARDS cohort. This 30,000 person cohort began enrolling participants from the lower 48 States in 2003 and will follow them for 15 years, examining where they live and various health outcomes, like stroke for example.
In this study, the researchers wanted to take a snapshot of whether there were any associations between sun exposure, air temperature and cognitive health. So they captured data on residential history, yearly cognitive health surveys, air temperature and amount of sunlight from satellite and ground data from NASA.
After a about a median five-year follow up, they found that participants that lived in areas that got below the median amount of sunlight were at higher risk of cognitive decline (OR=1.23) than those living in areas above the median amount sunlight. The researchers found no statistically significant association between air temperature and cognitive decline.
The researchers concluded,
“The results of this analysis find that lower levels of solar radiation are related to increased odds of incident cognitive impairment…This longitudinal analysis used a large cohort to give evidence of a significant and novel relationship between reduced sunlight exposure and cognitive decline.”
They note that possible mechanisms for this cognitive decline include either lack of vitamin D or a mechanism involving circadian rhythm regulation. While vitamin D is an exciting and potential explanation, the researchers point out that much research still needs to be undertaken to prove this relationship and that for the time being, this study strictly demonstrates the benefit in living in sunny climates.
Obvious limitations of the study include potential for a multitude of confounders, lack of taking air pollution into account, and poor ability to track individual’s true exposures to sunlight.