Researchers have confirmed that a shortage of sunshine makes people more vulnerable to “winter blues,” as well as the more serious seasonal affective disorder.
“Daylight is effectively a natural antidepressant,” Dr. Brenda McMahon of Rigshospitalet in Copenhagen, Denmark, wrote in the journal European Neuropsychopharmacology.
She explained: “Like many drugs currently used against depression, more daylight prevents serotonin (from) being removed from the brain.” Medical News Today noted that serotonin is “the so-called happiness neurotransmitter.”
Past studies showed that people with the gene 5-HTTLPR are more likely to contract seasonal affective disorder (SAD). The gene is linked to a serotonin transporter that regulates the release of the substance from the brain. Slowing the release rate relieves depression. Most antidepressant drugs are designed for that purpose.
The Denmark research team set out to learn why some people who are at genetic risk of depression do not suffer from the condition.
McMahon wrote: “We found that the level of serotonin transporter protein dropped by an average of around 10 (percent) from summer to winter, with the drop being noticeably greater in women. We found that some people (could) control how much serotonin transporter was produced.”
SAD affects more than 16 million people in the United States every year. That is 6.7 percent of the country’s population. About 80 percent of patients are women, probably due to genetic factors.
“Winter blues is a general term, not a medical diagnosis,” said Dr. Matthew Rudorfer, a mental-health expert at the National Institutes of Health. “It’s fairly common, and it’s more mild than serious. It usually clears up on its own in a fairly short amount of time.”
Rudorfer made a distinction between the winter blues and SAD, which he described as “a well-defined clinical diagnosis (that) interferes with daily functioning over a significant period of time.”
Geographic location plays a large role. “In Florida, only about 1 percent of the population is likely to suffer from SAD,” Rudorfer said. “But … about 10 percent of people in Alaska may be affected.”
NIH researchers have long understood the connection between seasonal depression and sunlight. They believe excess darkness adversely affects the body’s circadian rhythm, or internal clock.
“This 24-hour ‘master clock’ responds to cues in your surroundings, especially light and darkness,” the agency wrote. “During the day, your brain sends signals to other parts of the body to help keep you awake and ready for action. At night, a tiny gland in the brain produces a chemical called melatonin, which helps you sleep. Shortened daylight hours in winter can alter this natural rhythm and lead to SAD in certain people.”
The most common treatment for the disorder, light therapy, substitutes bright artificial light for the sun. More than 70 percent of patients get relief from their symptoms.
“Some people say that SAD can look like a kind of hibernation,” Rudorfer said. “People with SAD tend to be withdrawn, have low energy, oversleep and put on weight. They might crave carbohydrates.”
The NIH website explains that SAD patients are often “gloomy,” with “hopeless” and “worthless” feelings that can make them “irritable.” As a result, they often stop enjoying their favorite activities and tend to avoid social situations.