Winter Solstice 2010: Good News for Those with "Winter Blues?" (PICTURES)

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(CBS) The 2010 winter solstice is here. For some, it's an astronomical curiosity. For others, it's about rebirth and ritual celebration. But for the estimated five percent of the population who suffer from seasonal affective disorder, the shortest day of the year means something else entirely:

The beginning of the end of the saddest time of the year.

PICTURES: Simple Help for Seasonal Affective Disorder

No one knows the exact cause of seasonal affective disorder (SAD). But experts say it arises when the body's internal clock falls out of sync with "clock time" - the result of winter's short days and late dawns. About five percent of the population feels "winter blues" quite acutely, with another 15 percent suffering a milder form.

What's it like? A lot like "having jet lag for five months," says SAD specialist Dr. Alfred Lewy, professor of biological psychiatry at Oregon Health and Science University.

Fortunately, Dr. Lewy tells CBS News, there are ways to overcome symptoms of the disorder, which include carbohydrate cravings, weight gain, difficulty waking, and social isolation in addition to sadness. Getting plenty of sleep, exercising regularly, and taking other simple lifestyle approaches can help, as can antidepressant medication. But for many SAD sufferers, the treatment of choice is light therapy, which involves sitting in front of super-bright fluorescent lights for an extended period of each day during the winter months.

How effective is light therapy? Studies show that up to 80 percent of users show complete remission of symptoms, according to the website of the National Association of Mental Illness.

PICTURES: Simple Help for Seasonal Affective Disorder