I have a friend who has seasonal affective disorder. She lives in the North, and it has been a very bad year for people with her disorder. Her husband is worried about her and next winter. What can he do to help her, and what can I do, to make her next winter better?

-- Victoria

Seasonal affective disorder (or SAD) is a recurrent pattern of seasonal depression. It manifests most commonly as depression during the winter, although a few people experience summer mood changes. SAD is thought to be caused by a sensitivity to the change in sunlight exposure as days shorten or lengthen during the year. Winter SAD lifts as the days lengthen in spring and summer, while summer SAD lifts as days shorten in fall and winter.

In addition to having typical features of depression such as fatigue, carbohydrate craving, sleep disturbance and social withdrawal, SAD sufferers may experience a weakened immune system and be more likely to become physically ill. (Summer sufferers may experience increased energy -- approaching mania -- and decreased sleep.)

Light therapy has been found very effective for SAD, so your friend may benefit from purchasing and using an artificial light box or other such device. Light therapy devices are designed to increase retinal (eye) exposure to light in morning or afternoon, sometimes actually simulating dawn or twilight. This regulates blood levels of the neurotransmitter serotonin and the hormone melatonin, substances that affect mood, sleep patterns and sleep quality. The treatment may run from 15 minutes to three hours once or twice per day, depending on the person and the type of light device. A psychiatrist experienced with SAD may be able to direct you to such devices and suggest how best to use them.

There are also reports that daily outdoor exercise, such as hour-long walks, help alleviate SAD. One way you and your friend's husband might help her this fall and winter is by taking turns accompanying her on daily walks outside in the daytime. You can also encourage her to eat a balanced diet and decrease the stress in her life. Psychotherapy, particularly cognitive-behavioral therapy, and antidepressant medication may also help.