For eight years, nearly 30,000 people were questioned throughout China. Their life satisfaction and mental state were compared to the hours of sunshine of the day and the previous week. And yes, the bright days seem to play a small role in our well-being … but not as much as one could imagine.
A giant weather survey on human happiness
To answer the question “Does the sun make us really happier?“, Researchers have crossed two databases: that of the China Family Panel Studies (CFPS) and that of the country’s weather stations. Result: a long study of eight years, conducted between 2010 and 2018, analyzing the responses of almost 30,000 people interviewed at different seasons and in all regions of the country.
Each participant noted his life satisfaction on a scale of 1 to 5, and some have fulfilled a questionnaire evaluating eight recent depressive symptoms (sadness, solitude, disturbed sleep, etc.). These responses were meticulously paired with the amount of sun received, recorded by 824 weather stations spread over Chinese territory.
The sun was classified in five categories: 0 to 3 hours, 3 to 6 am, 6 to 8 a.m., 8 to 11 a.m., and more than 11 a.m. It was the beach 6 to 8 hours that served as a reference. The researchers then checked a large number of variables such as age, income, air pollution, temperature, humidity or precipitation to isolate the real effect of the lack of sun.
Sun of the day or radiant week, which one acts the most?
First observation: the link between sunshine and life satisfaction is very real, but remains modest. The people interviewed on the brightest days (more than 11 hours of sun) declared satisfaction slightly higher than those who responded in covered weather. Conversely, gray days with less than 3 hours of sun coincided with a slight drop in this satisfaction. The effects seemed linear: the more sun, the more people declare themselves happy. But these differences remain subtle: a few tenths of points on a scale of 1 to 5.
As for depression, this is another story. The sunshine of the maintenance day had no measurable impact on depressive symptoms. It is the average sun received during the previous week that made a small difference. By combining very sunny days (more than 11 hours), the researchers noted a slight decrease in depressive scores – of the order of a point fraction on a scale ranging from 0 to 24. These results tend to show that if a beautiful day can brighten up mood, it is above all prolonged exposure to light that seems to act, at homeopathic dose, on deeper morale.
Here is what we retain figures:
- Life satisfaction: increases slightly from 8 hours of sun per day;
- Less than 3 hours of sun: downward satisfaction;
- Depressive symptoms: no immediate effect, but low improvement after a very sunny week;
- Measured effects: a few tenths of a difference, statistically significant but modest.
Some profiles more feel the effects of the sun than others
The study did not stop at a national average. The researchers have identified subgroups more sensitive to light variations. First group: people working outdoors. Farmers, workers, employees on construction sites … Their daily well-being seems strongly correlated with the sun exposure, probably because of their work environment. No more light = more satisfaction, but also fewer depressive symptoms.
Another reactive population: families with young children. They also brought in additional satisfaction on sunny days. The authors advance a hypothesis: these families spend more time outside, and their morale therefore fluctuates more with the weather. Finally, the elderly saw their depressive symptoms drop a little more clearly after a bright week, while young people were more influenced by the sunshine of the same day.
To ensure the solidity of their conclusions, the researchers led several reliability tests: no correlation between the sun of the following days and well-being (which eliminates the opposite biases), similar results even by limiting the sample to the interviews carried out after 19 hours.
The effect of the sun exists, but it should not be overestimated. It improves morale and reduces signs of discomfort a little when it extends, but slightly. In short, a regular dose of natural light does not replace social ties, financial security or physical health, but it contributes to it in its own way, like a little daily time.