When the days get short and the weather turns nasty, many people feel sad. Psychologists have a name for the winter blues.

Appropriately, they call it seasonal affective disorder, or SAD for short. There’s a wide range of people afflicted with the condition, from about 1 percent in Florida to nearly 10 percent in New Hampshire.

Those who suffer complain that they have very little energy and feel lethargic or even hopeless. They may spend more time in bed, and may find that they crave carbs.

Giving in to those cravings can lead to seasonal weight gain along with the blues. The primary difference between SAD and depression is that winter blues usually lift once spring arrives.

This pattern has led to a hypothesis that SAD is a reaction to less exposure to daylight. In fact, it can sometimes be significantly helped with full-spectrum light therapy.

There is a range of light boxes that can be used for home treatment of seasonal depression.

Vitamin D also is in short supply in the wintertime, and a relative deficiency of this critical nutrient may also play a role.

Low vitamin D levels have been associated with depression, and boosting them with supplements sometimes results in an improved mood.

Although there are few well-controlled scientific studies to prove vitamin D has antidepressant effects, this is a low-risk approach to a serious problem.