Dreary, dismal days without the sun may do more than dampen our spirits. They might just impact the cognitive skills of those who battle depression, according to some new work that appears in the July 28 online issue of Environmental Health.
This is the first research to try and link light exposure and cognition, though earlier studies have shown that our mood can depend on the amount of sun we see (Seasonal Affective Disorder SAD)
The work involved a team of American researchers led by Shia Kent of the University of Alabama at Birmingham who used cross-sectional data for 14,474 people over 45 years old participating in a project investigating stroke incidence and risk factors, to look for links between depression, cognitive function and sunlight.
The team employed NASA weather data for the United States to check for match-ups between the days of bright sunlight and levels of cognitive functioning in those with, and without, depression.
The cognitive function of the subjects was measured using a validated questionnaire; an accepted depression scale assessed depression. Once the data was collected, advanced statistics were used to assess any link between average sun exposure and cognitive function.
Kent summarized the findings of the team, "We found that among participants with depression, low exposure to sunlight was associated with a significantly higher predicted probability of cognitive impairment. This relationship remained significant after adjustment for season. This new finding that weather may not only affect mood, but also cognition, has significant implications for the treatment of depression, particularly seasonal affective disorder".
Seasonal affective disorder, SAD, is a relative newcomer to the scene, first referenced in print back in 1985, and is known to bring depressive symptoms as the days grow shorter in the fall and winter, with symptom improvement as spring returns.
At higher latitudes more people are diagnosed with as they are exposed to less sunlight and colder and harsher winters.
Women are more often diagnosed with this form of depression than men. For symptoms to receive an official diagnosis of SAD, they must repeat for two years in a row, without depression at other times of the year.
The researchers speculate that cognitive impairment brought on by depression and lack of sunlight might improve using the same light therapy as with SAD.
Earlier work has shown a strong link between SAD and other lingering forms of depression. It's also accepted that depression often becomes more pronounced during the darker months of the year.
The study also confirmed melatonin and serotonin, both already implicated in depression, as being involved in cognitive function issues.
These two brain chemicals have been named as factors in serious brain diseases like Alzheimer's and Parkinson's, as well as sleeping disorders. Cerebral blood flow has also been implicated in cognitive functioning; earlier work confirming that such blood flow is affected by light.
Also of note, the relationship between sunlight and cognitive function didn't hold true for those who weren't depressed, according to the research. This suggests that it may be that the same mechanisms involved in depression might also be involved in cognitive functions.
If you are depressed, or deal with SAD, trying to spend some time in the sun (safely, of course) is a simple way to put the findings of this intriguing research to the test for yourself. You might also consider learning more about light therapy, which would have you sitting comfortably under a full spectrum light for a few hours a day all through the winter months.
Also good is a walk outdoors, even in the cold, as it can be a refreshing, invigorating source of natural sunlight and keep Seasonal Affective Disorder SAD at bay.