No energy, feeling moody and wanting to be alone are all signs of seasonal depression called seasonal affective disorder, or SAD.  Half a million people suffer from it, but there are some simple ways you can help prevent and treat this condition.

First is to exercise.  Keeping a healthy routine during winter can help fight against the sluggishness SAD can bring. Doctors recommend yoga or a walk outside.

Next, stay social. SAD is associated with isolation, so remaining social throughout the winter can help.

And if all else fails, try light therapy.  SAD is believed to be caused by declining light levels interfering with the body’s natural rhythms.  Daily exposure to a high-intensity light source may help curb some of the effects.

Vitamin-D levels are also believed to be associated with the disorder.  Your body normally creates the vitamin with exposure to sunlight, so your levels might be low in the winter.  A blood test can tell your doctor if supplementation could be necessary.  Light therapy also helps raise vitamin-D levels.