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Why is it so hard to wake up on winter mornings?

We need to sleep the same hours in both summer and winter, but the cold and darkness favor sleep. If you haven’t slept well or enough, getting out of bed is more difficult

Por qué cuesta tanto despertarse en las mañanas de invierno
Hitting the snooze button only delays the inevitable.Westend61 (Getty Images/Westend61)

If fruit flies had little alarm clocks that went off when they had to get up for work every day, they would feel the same way in the winter that humans do when it happens to them: their tiny sheets would stick to them. But, because they are not tied to the tyranny of an alarm, when it is cold and dark, they simply wake up later.

In the dark and cold months, with the alarm clock set at the same time as in summer, it is easy to wonder when it rings if we shouldn’t do like the sun, fruit flies, and other animals that also sleep more in winter and set the alarm for later. Is this drowsiness due to the fact that we need more hours of sleep during this season?

A study, published at the beginning of the year in Frontiers in Neuroscience, objectively measured the sleep of the participants (using polysomnographies). All had different sleep disorders, were in an urban environment, and did not set an alarm clock. Throughout the year the study concluded that, although the participants slept more in winter, it was not a very significant amount of extra time. What was noticeable was a change in the architecture of sleep, or the distribution of the time we spend in sleeping phases. In winter, participants spent more time in the REM phase. If these results were also obtained when studying people without sleep disorders, the study indicates, it would be the “first evidence on the need to adjust sleep habits to the seasons.”

However, sleeping more or finding it harder to get out of bed does not necessarily mean that we need more sleep. “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 and member of the chronobiology research group at the University of Murcia. That is to say, the winter environment, with more hours of darkness, favors sleep. The expert says that it is something that we should take advantage of and perhaps go to bed earlier, if we can. “In general, Spaniards have a sleep deficit. We are below six and a half hours, while we should sleep between seven and nine hours,” he states. In fact, we sleep even less in summer when 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 increasingly longer. If we sleep more, it is normal to spend more time there.

The environment that promotes sleep is mainly influenced by light, which helps us synchronize with the circadian cycle. “When there is no sun, the body encourages the production of melatonin, the sleep hormone in humans,” says Martínez Madrid. If the alarm clock rings before dawn, or the room is completely dark, waking up is more difficult.

We usually have lower levels of vitamin D, which also has an influence, adds Noelia Ruiz Herrera, professor of Psychology at the International University of La Rioja (Spain), and currently on placement as a researcher with the Division of Sleep and Circadian Rhythm Disorders at Brigham and Women’s Hospital at Harvard Medical School. “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 and wake cycle, and our mood,” she explains. Seasonal affective disorder, feeling melancholic and even depressed in these months, can also make it difficult to get out of bed. “When is it worrying? When it influences our daily lives,” says Ruiz.

Changes in habits can also influence sleep. For example, if we do less physical exercise in winter, we will sleep worse, the expert warns, 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 suddenly turn on the light. The fruit flies at the beginning of this text also wake up when the light goes on, but, if it is cold, they go back to sleep. This was one of the checks carried out by researchers in a study published in 2020 in Current Biology. They detected a sensory system in the antennae of flies that detects cold and communicates it to the neuronal network that regulates sleep. Not only does light matter, but the ambient temperature too.

Does the cold of winter mornings also influence humans? The answer is somewhat more complicated, concedes Marco Gallio, associate professor of Neurobiology at Northwestern University and one of the study’s leaders. After all, humans wear clothes, sleep indoors, and cover themselves with blankets, so the effects of winter are somewhat more diffused. For this reason, he explains by email, light is considered the primary synchronizer of sleep in humans. “Still, the idea that fluctuations in external temperature can function as a synchronizer in mammals has been tested directly and has gained some experimental support,” he notes.

In the case of humans, a team made up of researchers from South Africa and the United States wanted to see if artificial light and modern life had ruined our sleep. To do this, they studied how three more or less isolated tribes sleep (the Hadza of Tanzania, the San of Namibia, and the Tsimane of Bolivia), 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 have over light: the time to go to sleep was not marked by the sunset, but by the drop in temperature. The tribes went to sleep not when it was dark, but about three hours later, when the temperature drop was noticeable. And, yes, they slept an extra half hour 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 favored in winter,” says María José Martínez Madrid. In the morning, however, the effect of temperature probably has more to do with not wanting to leave our warm bed if we feel like it is freezing outside it.

For Martínez Madrid, the conclusion is clear: we need the same hours of sleep, but in winter it is easier. “I always repeat that winter time is not bad, we should take advantage of it!” she insists. Of course, you know that the current pace of life and schedules make it difficult to go to bed earlier and wake up when we have had enough sleep. She gives the case of teenagers as an example. Teens need to wake up later. “Teenagers naturally tend to delay their time of going to sleep and getting up. However, in high school, instead of going in at 9:00 a.m., the poor souls enter at 8:00 a.m. in many places, which means they are going in the opposite direction from their body clock. If we adapted to them coming in at 10 in the morning, it would help a little to follow the rhythm that their body demands,” she points out.

Tips to wake up better during the winter

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