"Winter blues is a general term, not a medical diagnosis. 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," Dr. Matthew Rudorfer, a mental health expert at National Institute of Health, said in a statement. The so-called winter blues are often linked to something specific, such as stressful holidays or reminders of absent loved ones.
"Seasonal affective disorder, though, is different. It's a well-defined clinical diagnosis that's related to the shortening of daylight hours," Rudorfer said. "It interferes with daily functioning over a significant period of time."
A key feature of SAD was it follows a regular pattern. SAD is more common in northern than in southern parts of the United States, where winter days last longer.
"In Florida only about 1 percent of the population is likely to suffer from SAD. But in the northernmost parts of the United States about 10 percent of people in Alaska may be affected," Rudorfer said.
As with other forms of depression, SAD can lead to a gloomy outlook and make people feel hopeless, worthless and irritable. They might lose interest in activities they used to enjoy, such as hobbies and spending time with friends, Rudorfer said.
"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 "People with SAD tend to be withdrawn, have low energy, oversleep and put on weight.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, such as cakes, candies and cookies."