TUESDAY, July 28, 2009 (HealthDay News) -- A new study shows that gloomy days are linked with memory and other cognitive problems in people suffering from depression.
Previous research has shown that many people feel their moods shift with shifting skies, with more depression linked with less sunlight, but this is the first time that light exposure and cognition have been paired, stated the authors of a study appearing in the July 28 online issue of Environmental Health.
Light therapy, such as that prescribed for people with seasonal affective disorder (SAD), might also help people with cognitive impairments, the authors added.
"This is speculation, but those who have cognitive impairment could be helped with sunlight," said study author Shia Kent, a doctoral candidate at the School of Public Health at the University of Alabama at Birmingham.
"This is very interesting. I haven't seen a study exactly like this," said Dr. Richard Isaacson, an assistant professor of neurology and medicine at the University of Miami Miller School of Medicine. "We're always looking for anything easy and safe in terms of stimulating the brain. This is the beginning of something, although we definitely need more research and investigation."
Prior studies have demonstrated a strong link between SAD and other forms of depression, and even with rates of violent murders, suicides and aggressive behavior. Depression tends to become more pronounced in darker months, while aggressive behaviors tend to escalate in lighter months.
The effect of sunlight on cognition, however, has not been well researched.
The researchers used NASA weather data to see if there was any correlation between days of sunlight and levels of cognitive impairment in people with and without depression.
Their original hypothesis panned out: Depressed people who soaked up more of the sun's rays over a two-week period had better cognitive function compared with their counterparts getting less sunlight.
But the relationship did not hold true in people who weren't depressed.
"We think some of the same physiological mechanisms that affect depression also affect cognitive function," Kent said.
In particular, the authors have pinpointed the melatonin and serotonin hormonal systems as culprits. Both of these systems are also implicated in depression.
"These same hormone systems have been implicated in a number of mental disorders and cognitive disorders, such as Alzheimer's, Parkinson's and sleep disorders," Kent said.
"I'm an Alzheimer's doctor, and see a lot of patients with cognitive impairment," Isaacson said. "When people are a little depressed, they don't pay attention and if they don't pay attention, they're not going to remember things. Increased serotonin levels increase attention, which means you remember stuff better and the mind works better. It's a simple concept."
More information
The American Psychological Association has more on seasonal affective disorder.
