Rising Night Temperatures Cost Indians Up to 93 Hours of Sleep Annually, Study Finds

A new study has revealed that residents in India's largest cities are losing between 65 and 93 hours of sleep each year due to rising nighttime temperatures. The research, conducted by scientists from the University of Hyderabad and published in the journal The Lancet Planetary Health, analysed data from 2015 to 2023 across urban centres including Delhi, Mumbai, Kolkata, Chennai, Bengaluru, and Hyderabad.

The study found that nighttime temperatures in these cities have increased by an average of 0.5°C per decade, directly impacting sleep quality and duration. The highest sleep loss—93 hours per year—was recorded in Delhi, where summer nights often remain above 30°C. Even comparatively cooler cities like Bengaluru saw a loss of 65 hours annually.

“Sleep is essential for physical and mental health. Chronic sleep deprivation is linked to cardiovascular disease, diabetes, obesity, and impaired cognitive function,” said Dr. Priya Sharma, lead author of the study. “Our findings highlight a less-discussed consequence of climate change: the erosion of restorative sleep.”

The research used data from wearable sleep trackers and weather stations, adjusting for factors like income, air conditioning access, and urban heat island effects. The authors noted that low-income households, which often lack cooling facilities, are disproportionately affected. In many slums, residents reported sleeping on rooftops or streets to escape indoor heat, exposing themselves to safety risks and mosquito-borne diseases.

India has experienced a steady rise in mean temperatures over the past decade, with heatwaves becoming more frequent and intense. Nighttime temperatures, in particular, have risen faster than daytime highs due to increased humidity and urbanisation. The study projects that by 2050, sleep loss could exceed 100 hours per year in several cities if emissions continue at current levels.

The Indian government has launched initiatives such as the National Action Plan on Climate Change, but experts say more targeted policies are needed. “Urban planning must incorporate green roofs, reflective materials, and increased tree cover to mitigate heat retention,” added Dr. Sharma. “Public health advisories should also inform citizens about simple cooling techniques, like using damp cloths and fans, which can improve sleep without energy-intensive air conditioning.”

The study comes amid growing global attention to the health impacts of climate change. A 2022 report from the World Health Organization estimated that over 2 billion people worldwide experience inadequate sleep, with rising temperatures exacerbating the problem in low- and middle-income countries. India, with its dense urban population, is particularly vulnerable.

While the findings are concerning, they also offer an opportunity for intervention. “Simple behavioural changes and better city design can significantly reduce sleep loss,” said co-author Dr. Rohan Desai. “But without rapid decarbonisation, the problem will only worsen.”

The research team is now expanding their study to include smaller cities and rural areas, where data on sleep and temperature remains sparse.