Do the shorter, darker days make you cranky? Or put you in a bit of a funk?

It may mean you have a type of depression triggered by the calendar called Seasonal Affective Disorder, or SAD.

Dr. Obi Ikwechegh
Dr. Obi Ikwechegh

It's a byproduct of shorter days and longer nights this time of year. At least 3 million Americans – and probably many more – wrestle with SAD from September to March, according to Dr. Obi Ikwechegh at Novant Health Psychiatric Medicine.

"It can become for some patients pretty significant such that they actually become suicidal," said Ikwechegh (pronounced "e-quay-chay"). "Until you're really in treatment where your physician can help you see that it's every winter, most patients don't know that they have it."

What are the symptoms of SAD?

Patients with SAD "have all the hallmarks of a major depressive disorder," Ikwechegh said, "including irritability and anhedonia, which is not wanting to do things that you used to love to do, depressed mood, difficulty sleeping and appetite disturbance."

You might even crave carbohydrates and pack on some pounds.

What causes SAD?

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Sunlight regulates your sleep-wake cycle. When daylight hours begin to shrink in the fall, your body clock can get out of whack — even before daylight saving time ends. SAD is a sign your body is struggling with this natural seasonal reset.

The exact causes are unknown, but research points to some chemical culprits, according to the National Institute of Mental Health.

Some people with SAD make too much melatonin, a hormone that regulates sleep, and may have an imbalance of serotonin, a brain chemical that affects mood. They may also have low levels of vitamin D, the so-called "sunshine vitamin," NIMH says.

What's the best remedy for SAD?

Relief starts with a visit to your doctor, who will review your symptoms and make a diagnosis. He or she may prescribe an antidepressant and/or a vitamin D supplement and is almost sure to recommend light therapy.

Spending time — especially in the early morning and early evening — in front of a special therapy lamp that mimics natural sunlight can lift your mood and keep the winter blues at bay, Ikwechegh said. Some of her patients use a therapy lamp, on a timer, to wake them every morning. They set it to come on again when they get home after work. Some also have a small therapy lamp on their desk at the office.

"It's not just a matter of having extra light, though," Ikwechegh says. "The light has to approximate the sun's light."

Many insurers will cover some or all of the lamps' cost, but only with a doctor's prescription, Ikwechegh said.

Some SAD patients also respond well to seasonal adjustments to their usual medications and some benefit from therapy.

What else do people need to know?

The brain is just like any other organ in the body, meaning things can go awry, Ikwechegh says. If you think you have seasonal depression, don't be ashamed to get help. It doesn't mean you're weak or crazy..

"It would be different if we don't have a treatment, but we do," Ikwechegh says. "They could have a better life, frankly. Many, many people go through SAD every year, so there's an impact on your marriage, your children, your job, on yourself. It's worth it to get the treatment you need."