Air pollution can affect sleep quality, study finds

Air pollution is affecting how well people sleep, according to a global review of 1.2 million people across six countries.

The metastudy analysed 25 high-quality studies since 2015, covering people over 45 years old in China, India, the US, Germany and other nations.

Particle pollution, nitrogen dioxide and carbon dioxide were all linked to shorter or poorer-quality sleep, with effects more extensive than expected.

The review was led by Dr Junxin Li of the Johns Hopkins University School of Nursing.

Dr Li said: “For years our team has been studying sleep in older adults living in the Baltimore area.

“Outdoor air quality may change block-by-block and, in some residences, we noticed exhaust fumes from nearby traffic.

“This led us to a simple but critical question: could the air older adults breathe indoors – as well as just outside their front door – be influencing how well they sleep?”

Some studies measured sleep with wrist-worn devices while others used interviews, examining both short-term pollution changes and long-term exposure.

Nine studies with similar approaches were pooled into a single metastudy, enabling predictions about pollution-related sleep problems and possible benefits of cleaner air elsewhere.

The team calculated that halving average particle pollution (PM2.5) – from levels typically found on busy London roads down to World Health Organization guidelines – could reduce poor sleep in middle-aged and older adults by around 10 per cent.

Li said: “We can infer that cutting average particle pollution (PM2.5) in half – from typical levels found alongside busy London roads down to the World Health Organization guidelines – could trim the likelihood of poor sleep in middle-aged and older adults by roughly one in 10.”

Indoor air pollution also emerged as a key factor, though only six high quality studies examined this, mostly in China.

People using solid fuels such as wood or coal for heating and cooking reported worse sleep, including insomnia and shorter duration, compared to those using clean fuels.

One study found that extractor fans or simply opening windows during cooking reduced the effects on sleep.

UK studies have shown that wood-burning stoves leak fine particles into homes, while cooking – particularly with fossil gas – adds further indoor pollution.

Li said: “Current clean-air policies focus mainly on outdoor sources, but our findings make clear that the agenda must expand.”

Older people typically spend much of their time at home, making indoor air quality especially important for this group.

Li added: “Air quality – both outdoors and inside the home – is an underrecognised contributor to sleep problems in middle and later life.

“Sleep itself should be treated as a core health indicator when environmental regulations are evaluated, because cleaner air not only safeguards lungs and hearts, it also helps people sleep, supporting cognition, mood and overall resilience later in life.”