In the first week of November, Delhi’s air was so thick with pollution that it was visible and tangible and many of the city’s residents might have attributed the smog to their bad moods. But any emotional distress that they felt could have been more linked to the slightly shorter winter days than the lack of bright sunshine.

Scientists from Brigham Young University in the United States have found that the presence of pollution or rain or clouds do not affect mental and emotional health as much as the amount of time between sunrise and sunset. In other words, the intensity of sunlight does not matter as much as the duration.

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The study, published in the Journal of Affective Disorders, analysed six years of therapy data of 16,452 people along with environmental data. Th environmental data had 19 weather and pollution variables, including wind chill, rainfall, solar irradiance which is the amount of sunlight that hits the ground, wind speed, and temperature.

The researchers were surprised to find that other than sun time, no environmental factor were related to stress. The study also noted that greater sun time also trended mildly with lower suicide ideation.

The study was conducted among patients under therapy and not the general population. The findings are, however, applicable to a plethora of clinical psychological disorders and not just seasonal affective disorder. Seasonal affective disorders are types of depression that come and go in seasonal patterns. The symptoms are more apparent and tend to be more severe during the winter.

The researchers said that therapists should be aware that winter months will be a time for high demand for their services. “With fewer sun time hours, clients will be particularly vulnerable to emotional distress. Preventative measures should be implemented on a case-by-case basis,” said a press release released by the team.