Air pollutant exposure linked to glaucoma, cataracts and suicide

People who are exposed to high levels of air pollution are more likely to develop glaucoma and cataract, and may even have a heightened risk of death by suicide, according to pooled analyses of previous research.

While there is strong evidence that being exposed to polluted air is harmful to the heart and lungs, much less is known about the effects of air pollution on the eyes, even though they are directly exposed. Dr Ahmed Alnabihi, from King Khaled Eye Specialist Hospital and Research Center in Saudi Arabia, was keen to change this.

“Every day, we see patients losing vision to conditions like glaucoma and cataract,” said Alnabihi, who presented his findings at the 44th Congress of the European Society of Cataract and Refractive Surgeons (ESCRS) last month. “These diseases are labelled as ‘age related’ as though aging is the only culprit, but that always felt incomplete to me. If something environmental is accelerating these conditions, that changes our thinking and suggests we could take action to reduce the risks.”

The study is a systematic review and meta-analysis, meaning Alnabihi and his fellow researchers gathered together all existing research in this area and pooled the data together. This included 41 separate observational studies, drawing on data from millions of people across East Asia and the UK and including some of the largest eye health databases in the world.

The researchers looked at levels of several types of air pollution: particulate matter (PM_2.5 and PM₁₀), nitrogen dioxide (NO₂), sulfur dioxide (SO₂), ozone (O₃) and carbon monoxide (CO). They compared these with how many people were diagnosed with glaucoma, cataract or age-related macular degeneration.

Their results showed that the higher the levels of fine particulate matter (PM_2.5), the greater the risks of glaucoma. People living in the most polluted areas had up to 70% higher odds of glaucoma compared to those in the least polluted areas. People living in more polluted areas also face a consistently higher risk of developing cataracts — and the more pollution, the greater the risk.

“The clearest finding was for fine particulate matter — the tiny particles in smoke, vehicle exhaust and industrial pollution that are small enough to get deep into the body,” Alnabihi said. “For every meaningful step up in pollution exposure, the risk of glaucoma rose by around 8% and cataract by around 4%. The evidence for age-related macular degeneration was less consistent, although some research supported a link. Other pollutants, including nitrogen dioxide and ozone, showed weaker or more mixed associations.”

Providing a possible explanation for the findings, Alnabihi stated, “Fine particles are thought to cause inflammation and oxidative stress in the body. Over years of exposure, these effects may damage the optic nerve, which is relevant to glaucoma, or the lens, which is relevant to cataract. Unlike most other organs, the eye is directly open to the environment. The ocular surface — the tear film, conjunctiva and cornea — has no barrier between it and outdoor air. That makes the biological plausibility here stronger than for some other organs.

“These findings add weight to the case for tighter air quality standards and pollution-reducing measures such as green spaces and traffic reduction in cities. Every major clean air policy has been justified primarily on the grounds of cardiovascular and lung health. Our paper adds a new organ system to that conversation.”

But it’s not just eye health that has researchers concerned, with a separate study — published in the Journal of Epidemiology & Community Health — suggesting that exposure to air pollutants may heighten the risk of death by suicide and suicidal thoughts.

While the effect of environmental factors on mental health conditions such as depression and anxiety has been extensively studied, its potential role on the risk of suicide is less well understood. To strengthen the evidence base, researchers at the Centre for Public Health, Queen’s University Belfast, sought to find out whether air, noise, light and water pollution, as well as sociodemographic factors such as sex and income, might influence the risk of death by suicide and suicidal behaviours.

They scoured research databases for relevant studies published in English between January 2010 and April 2024. Out of an initial haul of 287, 45 met the eligibility criteria: 33 investigated death by suicide, while seven investigated suicidal thoughts and five investigated attempted suicide.

Pooled data analysis showed that short-term exposure to PM_2.5 (13 studies) and PM₁₀ (seven studies) and long-term exposure to PM_2.5 (six studies) and NO₂ (seven studies) were statistically significantly associated with risk of death by suicide, attempted suicide and suicidal thoughts. Evidence from a narrative review of 16 studies showed potential positive associations with other air pollutants, including SO₃ and O₃ as well as noise pollution.

Pooled data analysis wasn’t possible for the effects of water and light pollution, because of the limited number of studies and varying outcome measures; the narrative review findings for these exposures were inconsistent. There were no clear associations between sociodemographic factors and the risk of death by suicide or suicidal behaviours.

By way of an explanation for the findings, the researchers pointed out that air pollutants and water polluted with arsenic, lead, lithium or nitrate have been linked to neurological effects, including chronic inflammation and nerve damage, which can impair brain function and influence mood and stress resilience. It has also been suggested that traffic and other environmental noise and light pollution increase stress levels through disruption of the body clock.

The researchers acknowledged various limitations to their findings, including the small number of studies available on each respective outcome and the fact that the included studies varied considerably in methodology and design. Indeed, commentators have suggested the outcomes may actually reflect the fact that polluted areas are also often disadvantaged areas, with higher unemployment and poorer access to mental health care.

Nevertheless, the researchers said their findings “bring to attention the critical importance of recognising environmental exposures as modifiable risk factors within suicide prevention efforts”, and suggested that integrating environmental health into mental health policy “could play a vital role in reducing suicide risk and improving overall population mental wellbeing”.

If you are affected by any of the issues discussed in this article, Lifeline has a 24/7 crisis support service that can help. Please call 13 11 14.

Image credit: iStock.com/Werawad Ruangjaroon