As winter approaches and daylight hours grow shorter, people prone to seasonal depression can feel it in their bodies and brains.

“It’s a feeling of panic, fear, anxiety and dread all in one,” said Germaine Pataki, 63, of Saskatoon, Saskatchewan.

She’s among the millions of people estimated to have seasonal affective disorder, or SAD. Her coping strategies include yoga, walking and an antidepressant medication. She’s also part of a Facebook group for people with SAD.

“I try to focus on helping others through it,” Pataki said. “This gives me purpose.”

People with SAD typically have episodes of depression that begin in the fall and ease in the spring or summer. Changing the clocks back to standard time, which happens this weekend, can be a trigger for SAD. A milder form, subsyndromal SAD, is recognized by medical experts, and there’s also a summer variety of seasonal depression, though less is known about it.

In 1984, a team led by Dr. Norman Rosenthal, then a researcher at the National Institutes of Health, first described SAD and coined the term. “I believe that because it is easy to remember, the acronym has stuck," he said.

What causes seasonal affective disorder?

Scientists are learning how specialized cells in our eyes turn the blue wavelength part of the light spectrum into neural signals affecting mood and alertness.

Sunlight is loaded with the blue light, so when the cells absorb it, our brains’ alertness centers are activated and we feel more wakeful and possibly even happier.

Researcher Kathryn Roecklein at the University of Pittsburgh tested people with and without SAD to see how their eyes reacted to blue light. As a group, people with SAD were less sensitive to blue light than others, especially during winter months. That suggests a cause for wintertime depression.

“In the winter, when the light levels drop, that combined with a lower sensitivity, might be too low for healthy functioning, leading to depression,” Roecklein said.

Miriam Cherry, 50, of Larchmont, New York, said she spent the summer planning how she would deal with her winter depression. “It’s like clockwork,” Cherry said. “The sunlight is low. The day ends at 4:45, and suddenly my mood is horrible.”

Does light therapy help?

Many people with SAD respond to light therapy, said Dr. Paul Desan of Yale University’s Winter Depression Research Clinic.

“The first thing to try is light,” Desan said. “When we get patients on exposure to bright light for a half an hour or so every morning, the majority of patients get dramatically better. We don’t even need medications.”

The therapy involves devices that emit light about 20 times brighter than regular indoor light.

Research supports using a light that’s about 10,000 lux, a measure of brightness. You need to use it for 30 minutes every morning, according to the research. Desan said this can help not only people with SAD but also those with less-severe winter blahs.

Special lights run from $70 to $400. Some products marketed for SAD are too dim to do much good, Desan said.

Yale has tested products and offers a list of recommendations, and the nonprofit Center for Environmental Therapeutics has a consumer guide to selecting a light.

If your doctor diagnosed you with SAD, check with your insurance company to see if the cost of a light might be covered, Desan suggested.

What about talk therapy or medication?

Antidepressant medications are a first-line treatment for SAD, along with light therapy. Doctors also recommend keeping a regular sleep schedule and walking outside, even on cloudy days.

Light therapy’s benefits can fade when people stop using it. One type of talk therapy — cognitive behavioral therapy, or CBT — has been shown in studies to have more durable effects, University of Vermont researcher Kelly Rohan said.

CBT involves working with a therapist to identify and modify unhelpful thoughts.

“A very common thought that people have is ‘I hate winter,'" Rohan said. “Reframe that into something as simple is ‘I prefer summer to winter,'" she suggested. “It’s a factual statement, but it has a neutral effect on mood.”

Working with a therapist can help people take small steps toward having fun again, Rohan said. Try planning undemanding but enjoyable activities to break out of hibernation mode, which "could be as simple as meeting a friend for coffee,” Rohan said.

What else might work?

People with SAD have half the year to create coping strategies, and some have found hacks that work for them — though there may be scant scientific support.

Elizabeth Wescott, 69, of Folsom, California, believes contrast showers help her. It’s a water therapy borrowed from sports medicine that involves alternating hot and cold water while taking a shower. She also uses a light box and takes an antidepressant.

“I’m always looking for new tools,” Wescott said.

Cherry in New York is devoting a corner of her garden to the earliest blooming flowers: snowdrops, winter aconite and hellebores. These bloom as early as February.

“That’s going to be a sign to me that this isn’t going to last forever," Cherry said. "It will get better, and spring is on its way.”

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The Associated Press Health and Science Department receives support from the Howard Hughes Medical Institute’s Science and Educational Media Group. The AP is solely responsible for all content.