On the winter solstice, Dec. 21, the sun will set here on Cape Cod at 4:14 p.m. after rising about nine hours earlier, at 7:05 a.m.

Does 15 hours of darkness in a single day make you feel logy or even depressed? You might be suffering from Seasonal Affective Disorder, or SAD, a mood disorder first named in 1984. When the long nights of late fall and winter close in, SAD sufferers can grow lethargic and find themselves overeating and oversleeping. While some experience a mild case of the winter blues, others can be disabled by depression.

According to the Mayo Clinic’s website, more women than men suffer from SAD. The condition may run in families. And the farther you live from the equator, the worse your symptoms may be.

“New England is not the greatest place to live if you have a light problem,” says Carolyn Witt of Orleans.

Witt first became aware of SAD’s symptoms when she was in her 20s. Right around the time that the leaves fell off the trees, she started feeling lethargic. “In the winter I felt really blah, and toughed it out,” she said during a telephone interview last week.

She tried a number of natural remedies, but 10 years ago she and her husband bought a small house on the west coast of Florida where the sun sets almost an hour later. “It was a great solution,” she says of her seasonal travels. “I had no idea it would be so profound to move.” She also found a psychiatrist she liked and trusted.

For some SAD sufferers, the annual change of the clocks — this year on Nov. 6 — when daylight saving time ends, is a trigger, Witt says. “In October, a lot of people started saying, ‘I dread winter.’”

You might think it’s just a matter of feeling gloomy in the dark, but what happens to the body in the dark months is complex. It is thought that the circadian rhythm is disrupted by less exposure to sunlight. The body’s level of serotonin, which makes you alert and active, drops. Melatonin levels, produced during sleep, increase. When the hormones get out of whack, as the light changes between summer and winter, you can get depressed.

Witt recently founded a peer-led support group for those with SAD. It meets on Friday afternoons — before dark — at the Eastham Public Library. One coping strategy the group recently talked about is this: Whatever your favorite pastime is — reading, knitting, cooking — you can’t do it until the sun goes down. So at sunset you reward yourself.

“It’s too easy to flop in the chair and turn on the TV,” Witt says.

Or how about visiting one of our beautiful beaches at sunset?

“You can celebrate the sun and appreciate the sunset,” Witt says. She herself does this every other day. She also walks three times a day outdoors with her dog.

So if a lack of light is making you depressed, what if you could reintroduce that light? Enter light therapy, administered through portable home boxes.

Much research has been conducted to determine which types of light work best to mimic the lost hours of sunshine. In recent years lightboxes have improved, and a quick online survey shows that while you can spend up to about $230, the price has come down as low as $49. One lightbox, given a high rating by Consumer Tested Reviews, says that it “instantly” relieves symptoms by mirroring a full spectrum of sunlight rich in Vitamin D. People using this type of box spend 30 minutes in the morning by the light. No prescription is needed.

For Danielle Jeanloz of Chatham, who also feels the affects of SAD, lightboxes offer no relief. “Get a little sunshine daily, when possible, especially in the winter,” Jeanloz says, adding that even 10 minutes at midday can be energizing.

Jeanloz recommends a number of commonsense tips that have helped her such as taking in fresh air, eating healthy meals, getting enough sleep, and staying connected with friends and family. Jeanloz also takes vitamin D per her doctor’s recommendation.

“Volunteer if you can — it helps socialization and staying connected, feeling valued. And it’s enjoyable,” she says. “Recognize the ‘slump’ and be good to yourself” — even in small ways such as eating chocolate, or splurging on a massage. “By staying active and connected, the darker winter days go by quickly.”

Witt points out that the days will lengthen after Dec. 21, the winter solstice, also known as “the longest night.”

“I used to look at winter as this huge block of blah and gray,” she says. But knowing that each day is about a minute longer starting on Dec. 22 is “a crumb. Things are getting better.” To commemorate the solstice, Witt will host a celebration on Dec. 21 at 4 p.m. on Skaket Beach in Orleans. A fire, lights and drummers will mark the end of the shortening days.

Witt’s “Light Up Your Life” SAD support group meets at the Eastham Public Library at 190 Samoset Rd., on Fridays from 2 to 3 p.m. in the small conference room. All are welcome.