In the observational study, the effect that outside light has on the mood and sleep of more than 400,000 people belonging to the UK Biobank has been analyzed. The Biobank is a large-scale biomedical database and research resource containing detailed health and genetic information on half a million UK participants.
Participants were asked about their mood, what medications they took if needed, and how much time they spent outdoors on a typical summer and winter day. On average, participants reported spending two and a half hours outdoors, with early risers reporting the longest compared to night owls.
Previous research has shown that spending time outdoors and in nature has a number of health benefits, part of which could be related to the fact that natural light is the most important environmental time signal for the body’s circadian rhythms .
On the contrary, the lack of natural light could be a key factor that contributes to our slumps and sleep problems , both associated with depression, one of the main causes of disability worldwide.
“Humans evolved in an environment with a clear distinction between day and night, but our modern environments have blurred this distinction,” the group explains in their article.
Today, people spend “most of their waking hours in conditions of intermediate artificial lighting, due to reduced exposure to sunlight and exposure to relatively bright night light .” This situation can lead to sleep disorders since light affects melatonin, the hormone that promotes sleep, suppressing it.
In previous research by the same team of scientists, it was found that almost half of the homes in a Melbourne study had light bright enough to suppress melatonin by 50%, although it is true that it does not. Everyone is affected by artificial light in the same way.
In this latest study, Sean Cain from Monash University in Melbourne and his team wanted to verify the relationship between hours of the day spent outdoors and mood, sleep quality and health in general, a factor less studied than the effects negatives of night light.
The analysis showed that receiving more light anytime between sunrise and sunset was associated with better mood and better sleep, as well as a lower risk of depression and less use of antidepressant medications .
Each additional hour of natural light was also associated with lower chances of depression throughout life, lower use of antidepressants, and greater happiness. And those who reported being in a better mood and sleeping with more outside light tended to do so again the second time they were surveyed, an average of four years later.
The results on the sun are somewhat to be expected, based on what we know about light, nature, sleep patterns, and moods, but what is encouraging is to see such a large study demonstrating the effects of spend more time outdoors. Of course, it is an observational study in which the participants have to answer about their daily and health habits, so the answers they give may differ from what they actually do .
Fuente: Angus C. Burns, Richa Saxena, Céline Vetter, Andrew J.K. Phillips, Jacqueline M. Lane, Sean W. Cain, Time spent in outdoor light is associated with mood, sleep, and circadian rhythm-related outcomes: A cross-sectional and longitudinal study in over 400,000 UK Biobank participants, Journal of Affective Disorders, https://doi.org/10.1016/j.jad.2021.08.056.
