Winter in the mountains can be a uniquely invigorating time. With winter comes snow, and with snow comes skiing, snowboarding, snowshoeing, snowball fights, and more. So why, you might be asking yourself, does your heart sink every day with the ever-earlier sunset? Why don’t you feel like doing much other than curling up in bed under a thick blanket, maybe with a sweet treat?

If this sounds like you, you might be feeling the winter doldrums. And you’re in good company: about a quarter of Americans experience some kind of winter-related blues, impacting their mood, sleep, and appetite.

But why does the changing of the seasons bring such sadness to so many people?

The answer may feel intuitive: darkness. And not just because it’s miserable to drive to and from work in the dark (though that’s a part of it). The lack of sunlight that comes with shorter winter days messes with our bodies and our heads—some people more than others.

Vitamin D, which we get from sunlight, helps us produce serotonin, a chemical which helps provide a sense of well-being, as well as regulate sleep and appetite. Without enough sunlight, as in the winter, we can run short of this “happy chemical.”

Scientists think seasonal depression also has to do with the regulation of the hypothalamus, the part of the brain that deals with the circadian rhythm, or our “body clock.” Cells in our eyes that react to sunlight directly impact the hypothalamus. Sunlight kicks our body clock into gear, telling our bodies to wake up and be alert; when less light enters the eyes, as the day fades, it tells us to get sleepy.

But without enough sunlight throughout the day to send those initial “wake up” messages, the hypothalamus can get thrown out of whack. If you’re feeling down in the dumps as the days grow shorter, it might be because your confused hypothalamus is producing too much melatonin and not enough serotonin, leading to fatigue at all the wrong times. It can also induce feelings of sadness.

Generally, the best and simplest thing to do to help reduce those winter blues is to get out and soak up the sun for the few hours it’s out. But you don’t have the time or opportunity to get outside during our limited daylight hours, indoor plants can help. In several studies, houseplants were shown to have a measurable positive effect on peoples’ moods, reducing their blood pressure and levels of cortisol, a stress hormone. Get a plant for your desk or your living room, and remember those long days that’ll come back before we know it!

Despite facing 4 p.m. sunsets in December, we’re lucky: Colorado’s winter days are some of the sunniest in the country. Even though the sun sets early, a high percentage of our short days are bright and sunny. This is a good place to fight the winter doldrums! This winter, starting in mid-December, come over to Walking Mountains in Avon or to the Nature Discovery Center at the top of the Eagle Bahn Gondola for a sunny snowshoe tour with us!

Ella Spungen is a Naturalist at Walking Mountains who can’t imagine a sunny winter after 23 years in the dreary Northeast, but is thrilled to find out what it’s all about.