OverviewLike many people, you may experience cabin fever during the winter months. Or, you

Overview

Like many people, you may experience cabin fever during the winter months. Or, you may tend to eat more and sleep more when the temperature drops. But, seasonal affective disorder(SAD)goes well beyond those symptoms. SAD is much more than the winter blahs. It's a type of depressive disorder.

If you have SAD, winter's short days and long nights may induce feelings of depression, lethargy(嗜睡), fatigue, cravings for sweets and starches(淀粉类食物), headaches, sleep problems and irritability. Exactly how many people have SAD isn't really known, but it's estimated that about 6 percent of Americans suffer from winter SAD, and another 10 percent to 20 percent may experience mild SAD symptoms. The disorder usually begins when you're a young adult. It's also more common in women than in men.

What causes SAD is unclear, but it may have to do with the amount of sunlight you receive. Although SAD can affect people anywhere, it becomes more common the farther north you live--perhaps because these areas of the planet experience decreased daylight for months at a time. In some people, however, recurring episodes of depression may occur in the summer rather than in the winter.

Although there's no cure for SAD, there are treatments to help you successfully manage the condition so that you can go through the seasons of the year in relative comfort.

Signs and symptoms

SAD is a cyclic, seasonal condition, which means signs and symptoms are present only during a particular season of the year and then go away. Most of the time, the signs and symptoms of SAD appear during the winter and recede during the spring and summer.

But there are some exceptions to the rule. Some people have worsened signs and symptoms of depression in the spring. Other people--about one in 10--experience periods of mania(躁狂)or hypo- mania, a less intense form. of mania, during the summer. This is sometimes referred to as reverse SAD. Characteristics of mania may include persistently elevated mood, inflated self-esteem, hyperactivity and unbridled enthusiasm out of proportion to the situation.

If you regularly experience the following signs and symptoms when the seasons change, you may have SAD:

Winter SAD

Depression

Loss of energy

Social withdrawal

Increased sleep and sleepiness

Loss of interest in sex

Overeating, especially foods high in carbohydrates

Weight gain

Difficulty concentrating and processing information, especially in the afternoon

Summer SAD

Anxiety

Insomnia

Irritability

Weight loss

Decreased appetite

Causes

Doctors don't know the causes of SAD, but heredity, age and your body's chemical makeup all seem to play a role. So can the availability of sunlight. Researchers suspect that reduced sunlight may disrupt circadian rhythms that regulate your body's internal clock, which lets you know when it's time to sleep and when it's time to wake up. This disruption may cause depression. For example, winter depression is more common in people living in more northern latitudes, such as in Alaska, where the lengths of days and nights are more variable during the various seasons.

Some scientists have theorized that melatonin, a sleep-related hormone that's also linked to depression, might be the cause. Production of melatonin increases during the long nights of winter.

Other research suggests that lack of serotonin, a brain chemical(neurotransmitter)that seems to be triggered by sunlight, is the reason for winter depression. People who are depressed are known to have decreased levels of serotonin in their brains.

When to seek medical advice

Most people experience some d

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