Cold, rainy weather and gloomy days always trigger a flood of social media posts with photos of people curling up on the sofa with a blanket and a cup of hot tea to watch a movie or read a book. Why go outside unless you have to? The urge to stay home explains the consistent reports that Europeans and Americans spend 85%-90% of our time indoors. So say a 2003 European Commission population study, and a 2001 study published in Nature.
The number of hours we spend between four walls changes from season to season. If it’s not too hot, we spend more time outdoors in the summer, and we tend to stay inside in the winter, although a 2021 OnePoll survey says that this depends on our favorite season. Still, unless we work outdoors, we’re likely to spend, on average, 85-90% of our time indoors. What are we missing out on by not spending more time outside?
“Light synchronizes the circadian cycle,” said Dr. María José Martínez Madrid (University of Murcia, Spain), who coordinates the Spanish Sleep Society’s chronobiology (the study of biological rhythms) working group. To sleep well, it’s important to reduce exposure to light at night, but exposure to daytime light is equally important. “You should receive a minimum of two hours of natural light during the day, which is more difficult than it seems,” said Martínez. “If you aren’t exposed to light during the day, then melatonin is not synthesized at night. It [the circadian cycle] is a mechanism that needs this contrast – natural light during the day and darkness at night. We get drowsier and less physically active without this natural light exposure, and we don’t sleep as well at night.”
What’s needed is direct natural light exposure, and it shouldn’t be filtered through a window. “Even if we are exposed to light from a computer screen all day long, it’s not enough. This is blue light, which lacks the required intensity and full spectrum of light,” said Martínez.
Scientists also agree that time spent outdoors is related to healthier vision. A 2022 study concluded that the intensity of indoor light did not influence the development of myopia in children. In other words, the classic “you’ll ruin your eyesight by reading in the dark” admonition is a myth. But the study found that time spent outdoors did have an effect: more time outdoors protects against myopia in non-myopic children. This particular study did not find the same result for children that were already myopic, but another study did find that outdoor activity reduces myopia progression in school children.
Ophthalmologist Rosario Gómez de Liaño is the head of the strabismus (loosening or tightening the eye muscles in order to achieve proper eye alignment) surgical unit at the Hospital Clínico San Carlos (Madrid), president of the International Strabismus Society and a professor at the Complutense University of Madrid. She explained that the ultraviolet rays of natural light influence various physical mechanisms. “For example, there are different physical impacts to children reading indoors or outdoors because of the light, not because they were focusing their eyes at varying distances when they played outside,” said Gómez de Liaño.
The importance of mental health
A few months ago, a video went viral on TikTok and Instagram. It pictured a girl stomping along a snowy path to upbeat music with the caption, “Going on a stupid walk for my stupid mental health.” That’s the tiresome advice we always hear whenever we’re having a bad day – go get some fresh air.
“When we go out, we see that there is another world out there. This makes us realize that we could feel better if we went out more,” said Juan Ignacio Aragonés, a professor of social psychology at the Complutense University of Madrid and a member of PSICAMB, a Spanish environmental psychology association. The greater opportunity for social interaction can also increase our wellbeing, says Aragonés, who clarified that this is just common sense and is not based on scientific data.
But there is scientific data to prove Aragonés’ point. According to a 2021 study published in the Journal of Affective Disorders, more than 400,000 British participants in the study spent an average of 2.5 hours per day outdoors. Each additional hour outdoors was associated with less likelihood of depression and antidepressant use, lower frequency of anhedonia (reduced ability to experience pleasure) and despondency, less neuroticism and greater self-perceived happiness.
While this may mean that people tend to go out more when they are feeling good, there are indications that stupid walks can indeed help our stupid mental health. The relevant studies focus on three areas. The first is exposure to natural light, which regulates melatonin, serotonin and cortisol cycles. Since depression is related to alterations in these circadian cycles, regulating them could help stave it off.
There is also the relationship between the time we spend outdoors and physical activity. We tend to be more physically active when we’re outside, even if we’re just taking a walk, which contributes to feeling better. Lastly, the positive impacts of spending time in nature have been frequently studied, and according to a 2019 study, spending two hours a week in natural spaces has been linked to better health and greater overall wellbeing. This means that we get more benefit from outdoor time in a park or on a hike through the woods.
But what if that outdoor time is spent in an urban, polluted and stressful environment? According to a 2016 study published in the American Journal of Preventive Medicine, “study findings support the notion that increasing time spent outdoors may result in mental health benefits. However, this study questions whether that benefit is experienced equally among different groups, particularly given differences in occupational experiences and environmental characteristics of neighborhoods.”
Similarly, Dr. Rosario Gómez de Liaño mentioned a recent study that associates pollution to an increase in myopia. She says that many of these factors are still being researched, and cautions that “not all studies and journals are the same.” It remains to be seen what will bear out over time.
Ultimately, it seems clear that going out to a park or green space is better than a walk through city traffic on asphalt streets – personal health benefits expand in hospitable environments.