Study finds India is losing up to 93 hours of sleep every year: Doctor explains why

Sleep is one of the first casualties of rising temperatures and, unlike heatstroke or dehydration, the damage often goes unnoticed.

According to Dr Pradeep Bajaj, Sleep Medicine Specialist, Amrita Hospital, Faridabad, a recent study estimating that people living in India's major cities lose between 65 and 93 hours of sleep every year due to high night-time temperatures serves as an important reminder that climate change is also becoming an issue for sleep health.

The analysis, conducted by Climate Central, a global climate research organisation, examined how rising night-time temperatures are affecting sleep patterns across cities.

It found that several Indian cities are experiencing significant sleep loss linked to warmer nights, with Chennai recording the highest overall sleep loss among major Indian metros at around 93 hours annually, followed by Mumbai and Kolkata.

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The study also highlighted the role of climate change in worsening the problem. Cities including Bengaluru showed a strong climate change signal, with a measurable share of sleep loss attributed specifically to rising temperatures caused by global warming.

Why heat makes it harder to sleep

"The body is made to fall asleep only when the core temperature starts to fall. This cooling process is a natural biological cue that prepares the brain for deep, restorative sleep," says Dr Bajaj.

Hot and humid bedrooms throughout the night disrupt that process.

"People struggle to fall asleep, wake up more frequently, and spend less time in slow-wave and REM sleep, the two stages that matter most for memory, immunity, emotional regulation and physical recovery."

The body's inability to cool down efficiently during hot nights can interfere with the natural sleep cycle, affecting both sleep duration and quality.

The impact goes beyond a restless night

Dr Bajaj says sleep clinics are seeing an increasing number of people experiencing symptoms that may be linked to poor sleep quality caused by heat.

"In the sleep clinics we see more and more patients complaining of unexplained daytime fatigue, poor concentration, irritability and morning headaches despite spending seven or eight hours in bed. In many cases, the problem has not been the duration but the heat of the environment that has affected the quality of sleep."

Poor sleep quality can affect daily functioning, including concentration, mood, productivity and overall wellbeing.

Who is most at risk?

The effects of hot nights can be more pronounced among certain groups, particularly those who are already vulnerable to sleep disruption.

"This is even more apparent in older adults, children, pregnant women, people with obesity and those living with conditions such as obstructive sleep apnoea, hypertension, diabetes or cardiovascular disease."

Dr Bajaj explains that repeated sleep disruption can have wider health consequences.

"Repeated sleep disruption can cause worsening of blood pressure control, impaired glucose metabolism, increased levels of stress hormones and, over time, reduction of workplace productivity."

Simple ways to sleep better on hot nights

While air conditioning can help improve comfort, Dr Bajaj says it is not the only solution.

"To improve sleep quality on hot nights:

These measures can support the body's natural cooling process and help improve sleep quality during periods of high temperature.

Sleep should be part of the climate conversation

With night-time temperatures rising across Indian cities, sleep protection deserves greater attention as a public health concern.

"With nights in Indian cities getting warmer, sleep protection should be an important aspect of public health conversations. Sleep is not a luxury. It’s a biological imperative and, increasingly, one of the unseen casualties of a warming climate."

As climate change continues to affect daily life, protecting healthy sleep habits may become an increasingly important part of managing the health impact of rising temperatures.