Cloudy Skies May Cloud Your Thinking
< Jul. 29, 2009 > -- People suffering from depression have been found to have memory and other cognitive (thinking skills) problems during gloomy weather, according to a new report.
Past studies have shown that many people feel their moods shift with shifting skies, with more depression linked with less sunlight. However, this is the first time that light exposure and cognition have been paired, say the authors of a study appearing in the journal Environmental Health.
"This is speculation, but those who have cognitive impairment could be helped with sunlight," says study author Shia Kent, a doctoral candidate at the School of Public Health at the University of Alabama at Birmingham.
Light therapy, such as that prescribed for people with seasonal affective disorder (SAD), might also help people with cognitive impairments, the authors add.
A New Focus Using Sunlight?
"This is very interesting. I haven't seen a study exactly like this," says 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.
However, the effect of sunlight on cognition has not been well researched.
Research Looked at Weather Data
Kent's team used weather data from the National Aeronautics and Space Administration (NASA) to assess any correlation between days of sunlight and levels of cognitive impairment in people with and without depression.
The researchers were able to verify their original hypothesis: 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 they found that the relationship did not hold true in people who were not depressed.
Melatonin, Serotonin Involved?
"We think some of the same physiological mechanisms that affect depression also affect cognitive function," Kent says.
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 says.
"I'm an Alzheimer's doctor, and see a lot of patients with cognitive impairment," says Dr. Isaacson. "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."
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What is Seasonal Affective Disorder (SAD)?
Seasonal affective disorder, or SAD, is a mood disorder characterized by depression related to a certain season of the year - especially winter. However, SAD is often not described as a separate mood disorder but as a "specifier," referring to the seasonal pattern of major depressive episodes that can occur within major depression and manic depression.
SAD is a clinical diagnosis accepted in the medical community. Dr. Norman E. Rosenthal, Chief of Environmental Psychiatry Branch of the National Institute of Mental Health, is the researcher credited with discovering SAD.
Onset usually occurs during adulthood (with the average onset occurring at approximately age 23), and is four times more likely to affect women than men. According to Mental Health America, approximately 10 percent to 20 percent of the population suffers from mild winter SAD, and nearly 5 percent suffer from a more severe form of the disorder.
Decreased sunlight is thought to be part of the cause of SAD, and is under clinical investigation.
Two seasonal patterns of symptoms have been identified with SAD: a fall-onset type, also called "winter depression," in which major depressive episodes begin in the late fall to early winter months and remit during the summer months, and a spring-onset type, also called "summer depression," in which the severe depressive episode begins in late spring to early summer.
The following are the most common symptoms of SAD. However, each individual may experience symptoms differently. Symptoms may include:
The symptoms of SAD may resemble other psychiatric conditions. Always consult your physician for a diagnosis.
The treatments for "winter depression" and "summer depression" often differ, and may include any, or a combination, of the following:
Always consult your physician for more information.
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