Why It's So Hard to Wake Up on Winter Mornings

If fruit flies had to get up every morning when the alarm clock rings to go to work, in winter the same thing would happen to them as it does to many humans: the sheets would stick to them (in this exercise of imagination they also sleep covered on a bed). But, because they don't live tied to the tyranny of an alarm, when it's cold and dark, they just wake up later.

In the dark, cold months, with the alarm clock set to the same time as in summer, it's easy to wonder when it goes off if we shouldn't do like the sun, fruit flies and other animals that also sleep more in winter and delay the time of that alarm. Is this drowsiness due to the fact that we need more sleep in this season?

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A study published earlier this year in the journal Frontiers in Neuroscience, in which the sleep of participants – all with different sleep disorders, in an urban environment, without setting an alarm clock – was objectively measured (with polysomnography) throughout the year concluded that, although they slept more in winter, it was not a very significant extra time. What was noticeable was a change in the architecture of sleep, the phasing distribution of the time we spend sleeping: in winter, more time is spent in the REM phase. If these results were also given when studying people without sleep disorders, they indicate in the study, it would be a "first evidence of the need to adjust sleep habits to the seasons."

However, sleeping more or having a harder time getting out of bed doesn't necessarily mean we need more hours. "We always have the same need to sleep the same hours in winter as in summer, it's just that in winter we have more opportunity," says María José Martínez Madrid, coordinator of the Chronobiology working group of the Spanish Sleep Society (SES) and member of the chronobiology research group at the University of Murcia. In other words, the environment, with more hours of darkness, favors sleep, something that, the expert indicates, we should take advantage of and perhaps, if we can, go to bed earlier. "In general, Spaniards have a sleep deficit. We're under six-and-a-half hours, whereas we should be getting seven to nine hours of sleep," he says. It is, in fact, in summer when we sleep even less and we should try to sleep more. As for spending more time in the REM phase, the expert indicates that it is logical: in the successive sleep cycles that we have throughout the night, the REM phase is longer and longer. If we sleep more, it's normal to spend more time there.

This environment that favors sleep is mainly influenced by light, one of the synchronizers of the circadian cycle. "When there is no sun, what is encouraged is the increase in melatonin, a sleep hormone in humans," says Martínez Madrid. If the alarm clock goes off before dawn or the room is pitch black, that awakening is more complicated.

Vitamin D, which we tend to have lower levels in winter, also plays a role, adds Noelia Ruiz Herrera, a professor in the Bachelor's Degree in Psychology at the International University of La Rioja (UNIR) who is currently on a research stay in the Division of Sleep and Circadian Rhythm Disorders at Harvard Medical School's Brigham and Women's Hospital. "Lower levels of vitamin D, which are associated with less exposure to light, can also affect the production of serotonin, which is a hormone that influences our sleep-wake cycle and our mood," she explains. Seasonal affective disorder, that feeling melancholic and even depressed in these months, can also make it difficult to get out of bed. "When is it worrisome? When it influences our daily lives," Ruiz says.

Changes in habits can also play a role. If, for example, we do less physical exercise in winter, we will sleep worse, warns the expert, which will make it more difficult for us to get out of bed when the alarm goes off.

The Importance of Temperature

Another way to wake someone up, beyond making noise, is to turn on the light all at once. The fruit flies with which we started this text also wake up if you do that to them, but, if it is cold for them (18ºC), they go back to sleep. This was one of the findings made by those responsible for a study published in 2020 in the journal Current Biology, which detected a sensory system in flies that detects cold in the antennae and communicates it to the neural network that regulates sleep. It's not just the light that matters, but also the temperature.

Does the cold of winter mornings also influence humans? The answer is somewhat more complicated, concedes Marco Gallio, an associate professor of neurobiology at Northwestern University and one of the study's authors. Humans, after all, wear clothes, sleep indoors and cover ourselves with blankets, so the effects of winter are somewhat more blurred. For this reason, he explains via email, light is considered to be the primary sleep synchronizer in humans. "Even so, the idea that fluctuations in external temperature can function as a synchronizer in mammals has been directly tested and has gained some experimental support," he says.

In the case of humans, a team of researchers from South Africa and the United States wanted to see if artificial light and modern life had spoiled our sleep. To do this, they studied how three more or less isolated tribes (the Hadza of Tanzania, the San of Namibia and the Tsimane of Bolivia) sleep, whose way of life is similar to that of our ancestors. One of the most surprising results of the study, published in Current Biology in 2015, was the importance that temperature seemed to gain over light: the time to go to sleep was not marked by the sunset, but by the drop in temperature. They went to sleep not when it was dark, but about three hours later, when the temperature drop was noticeable. And, yes, they slept half an hour longer in winter.

Anyone who has spent sleepless summer nights because of the heat knows that temperature matters. "To sleep we need to cool our brain, we need the temperature to drop and for that we need the environment to be cooler than our interior. This is also favoured in winter," says María José Martínez Madrid. In the morning, however, the effect of temperature may have more to do with not wanting to leave a warm place if just by sticking out a finger we feel like we are freezing.

For Martínez Madrid, the conclusion is clear: we need the same hours of sleep, but in winter it's easier. "I always repeat that winter time is not the bad one, we should take advantage of it!" he insists. Of course, he knows that today's rhythms of life and schedules make it difficult to go to bed earlier or wake up when we've had enough sleep. He gives the example of teenagers, who need to wake up later. "Teens naturally tend to delay going to sleep and getting up. However, in high school, instead of entering at 9:00, the poor enter at 8:00 in many places, so we are going backwards in their clocks. If we adapted to them coming in at 10 a.m., we would follow the rhythm that their body asks them to do," he says.

Tips for waking up better in winter

• In the morning, expose ourselves to the light as soon as possible. This early reception of light, in addition to activating us, will help – thanks to the contrast between day and night, between light and dark, key to the circadian rhythm – so that at night we secrete more melatonin and sleep better, so we will wake up more rested, says María José Martínez Madrid. If we have to get up when it is still dark, the expert recommends light therapy lamps, which imitate daylight.
• Make the transition to the outside of the sheets less difficult. Noelia Ruiz suggests programming the heating to turn on 15 minutes before waking up, in addition to having "warm slippers or socks near the bed so you don't step on the cold floor."
• Do not swirl. While snoozing the alarm a few times isn't so clear that it's necessarily bad, it does nothing but delay the hard time of getting out of bed. Noelia Ruiz recommends "that the alarm be definitive" and, to force us to get out from under the duvet, "put the alarm clock on the other side of the room".
• Become physically active. Once out of bed, this would be ideal, "both to warm up and to activate us and to set the clock," says Martínez Madrid. He recommends, for example, walking to work if you can, which will also help if it is already daylight to receive light.
• Promote nighttime sleep. The better we have slept, the easier the morning will be. To do this, in addition to taking advantage of the darkness and trying, if possible, to go to bed earlier, it is also key to prepare the bedroom. "It's very tempting to turn on the heating in the bedroom at night when it's very cold, but let's remember that hot air and dry air can have undesirable effects on the quality of our sleep, because it dries out the mucous membranes of our nostrils. This causes us to have more snoring, which can be the beginning of a bad dream. We need to be in a relatively cool, dark room that allows the temperature to flow," explains Noelia Ruiz. In addition, exercising, maintaining regular times (going to bed and getting up, meals, sports, social life), hydrating well and trying to make dinner not too close to bedtime will also help to get a better sleep and an easier morning.

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