January 7, 2016 6:05 AM EST

Seasonal affective disorder (SAD)–a type of depression most prevalent in colder, darker months–affects roughly 15 million Americans each year. We asked Dr. Norman Rosenthal, a SAD expert and the author of Winter Blues, for tips to thwart it.

EAT SMART

Foods like legumes, oats and almonds–which have a low glycemic index–will give your body a long-lasting energy boost.

MAKE PLANS

In addition to talking with a therapist, which has been shown to relieve SAD symptoms, making plans with friends is a great way to avoid feeling isolated.

FIND LIGHT

Rosenthal suggests going for a 20-minute walk early in the morning, when natural light is brightest. There are also special light-therapy boxes that can illuminate an office or a cubicle.

STAY ACTIVE

Several studies have found that exercise can alleviate and even prevent depression, likely in part because of the release of feel-good chemicals in the brain.

–Alexandra Sifferlin

This appears in the January 18, 2016 issue of TIME.

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Contact us at letters@time.com.

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