This weekend, most Americans will get a gift that comes only once a year: an extra hour. At 2 a.m. Sunday, November 1, we’ll turn our clocks back to 1 a.m., officially ending daylight saving time. You can use that bonus hour to sleep, read, exercise, or stare at your phone for another 60 minutes. We have a pretty good idea which option will win.

But there’s a catch. While “falling back” is generally easier on our bodies than “springing forward,” changing the clocks still disrupts our internal rhythms. And the bigger issue isn’t what happens Sunday morning. It’s what happens during the next several months as daylight becomes increasingly scarce.

As we have mentioned often before, sunlight does considerably more than help us see where we’re going.

Your body doesn’t own a watch.

Our bodies operate on an internal 24-hour clock called the circadian rhythm. It helps regulate when we sleep and wake, but it also influences body temperature, hormone production, appetite, metabolism, and mood.

The clock is located in a small region of the brain called the suprachiasmatic nucleus (no need to pronounce or even remember this), which receives information about light through our eyes. Morning light tells our brain it’s time to be awake and alert. Darkness helps trigger the production of melatonin, the hormone that signals it’s time to sleep.

When we change the clocks, we change the timing of those signals relative to our daily routines. Our bodies don’t immediately get the memo.

The reason falling back is usually easier than springing forward is that we’re shifting our schedules an hour later, which is closer to the natural tendency of our internal clocks. That extra hour can help those of us who aren’t getting enough sleep.

Some people will find themselves waking up at 5 a.m. instead of 6, getting hungry an hour before dinner, or feeling ready for bed before the evening news. Most of us will adjust to the shift within a few days.

The real problem is the disappearing daylight.

Turning back the clocks doesn’t actually make the days shorter. The Earth’s tilt takes care of that all by itself. But as our planet’s movement reduces daylight in this part of the world, the time shift adds insult to injury (if you’re not a vampire) by shifting an hour of increasingly scarce daylight from the evening to the early morning. This makes the loss of afternoon sunshine feel especially abrupt.

And that can have consequences well beyond our sleep schedules.

Mood and motivation. Sunlight influences the brain systems that regulate serotonin, a chemical involved in mood. Reduced daylight may contribute to changes in serotonin activity and melatonin timing, leaving some people feeling less energetic, less motivated, or generally gloomy.

For some, these changes are mild. For others, they can develop into seasonal affective disorder (SAD), a form of depression that typically begins in the fall or winter and improves in spring. The American Psychiatric Association estimates that about 5% of American adults experience SAD, with higher rates in northern states.

Sleep and energy. Longer nights don’t necessarily mean better sleep. Reduced exposure to morning light can make it harder for our bodies to maintain a consistent sleep-wake rhythm. Some people sleep longer but still feel tired. Others find themselves waking too early or struggling to fall asleep at their usual bedtime.

Appetite and metabolism. Our circadian rhythms also help regulate insulin sensitivity, blood sugar, and the hormones involved in hunger. When those rhythms become disrupted, metabolic regulation can suffer. People with winter-pattern SAD may also experience increased appetite and cravings for carbohydrates.

Vitamin D. Our skin produces vitamin D in response to ultraviolet B rays from sunlight. During winter, especially in northern parts of the country, the sun may be too low in the sky for us to produce much vitamin D, even when we spend time outdoors. Vitamin D is essential for bone health, muscle function, and normal immune function. Low vitamin D isn’t necessarily the cause of winter fatigue or depression, and supplements haven’t consistently been shown to relieve seasonal depression. But finding ways to naturally produce more vitamin D can be very helpful.

You need your daily dose of daylight.

A fascinating 2021 study using data from more than 400,000 participants in the UK Biobank found that people who spent more time in outdoor daylight reported fewer depressive symptoms, better sleep, and less insomnia. The study was observational, so it couldn’t prove that sunlight caused those benefits, but the findings reinforce what we know about the importance of light to our internal clocks.

And here’s something worth knowing: Even on a cloudy day, outdoor light is typically much brighter than indoor lighting. A reasonably well-lit office might provide 300 to 500 lux, a measure of light intensity. Outdoor daylight can deliver thousands of lux, even when the sun isn’t shining.

In other words, sitting next to a window is nice, but getting outside is usually better.

So how do we make the most of the daylight we have?

• Get outside early. Try to spend 15 to 30 minutes outdoors in the morning, especially during the first hour or two after waking. Even a short walk can help synchronize your internal clock. You don’t need to stare at the sun, and you should continue protecting your eyes and skin.
• Take a daylight break. If your workday keeps you indoors, consider moving your lunch break outside or taking a short afternoon walk. Daylight and physical activity are a particularly useful combination.
• Keep moving. Exercise helps regulate sleep, improves mood, and supports metabolic health. It also helps counter the tendency to become less active during colder months. You don’t have to exercise outdoors, but combining the two gives you additional benefits.
• Don’t let winter change your entire schedule. Consistent bedtimes, wake times, and mealtimes help reinforce your circadian rhythm. Try not to compensate for the darkness by sleeping half the weekend away.
• Make evenings darker. Bright light late at night can delay melatonin production. Dim the lights, reduce screen brightness, and give yourself a reasonably dark bedroom. Your brain needs a clear distinction between daytime and nighttime.
• Stay connected. Shorter, colder days can make staying home particularly appealing. But social interaction and regular activities are important for mental health. Make plans, see friends, and resist the temptation to hibernate until April.

What about light therapy?

For people who struggle with winter depression, a light therapy box may help. These devices provide very bright light, typically 10,000 lux, without the ultraviolet radiation associated with sunlight.

Treatment generally involves sitting near the light for about 20 to 45 minutes shortly after waking. Light therapy has been used for decades to treat seasonal affective disorder, and many people find it helpful.

But timing matters, and light therapy isn’t appropriate for everyone. People with bipolar disorder, certain eye conditions, or medications that increase light sensitivity should consult a healthcare professional before trying it. And a light therapy box is not the same as a tanning bed, which we definitely don’t recommend.

What about the latest research on red light?

There’s also some intriguing emerging research suggesting that red and near-infrared wavelengths of light may influence the mitochondria, the structures inside our cells that produce energy.

In a small 2024 experiment involving 30 healthy participants, researchers at University College London found that a brief exposure to a specific wavelength of red light before a glucose tolerance test reduced the subsequent rise in blood glucose.

That’s interesting, but it’s very early research. It doesn’t establish that modern LED lighting causes metabolic disease or that replacing your light bulbs will improve your health. We have much stronger evidence for the benefits of natural daylight and maintaining healthy circadian rhythms.

For now, the best light therapy for most of us is still the free kind available outside.

This weekend, fall back gently.

You probably don’t need an elaborate strategy to handle Sunday’s time change. Try to maintain your usual sleep schedule, get some morning sunlight, and avoid turning that extra hour into an excuse to stay up even later Saturday night.

If you’re especially sensitive to changes in your sleep schedule, shifting your bedtime and mealtimes 15 or 20 minutes later over the next few days may make the transition easier.

And remember, feeling a little sluggish as the seasons change is common. Persistent sadness, significant fatigue, or loss of interest in activities you normally enjoy shouldn’t simply be dismissed as the winter blues. Seasonal depression is real, and effective treatments are available.

The good news is that we don’t have to surrender our energy and good moods just because the sun decides to call it a day at 5 p.m. A little planning, regular activity, and some strategically timed daylight can make the darker months considerably easier.

And if all else fails, there’s always the comforting thought that the days start getting longer again on December 22!