Cooking with coal or wood associated with increased risk of major eye diseases: study

China – A study involving nearly half a million people in China reveals a clear link between cooking with wood or coal, and an increased risk of major eye diseases that can lead to blindness, according to a report published in PLOS Medicine.

The researchers from the University of Oxford’s Nuffield Department of Population Health and the Chinese Academy of Medical Science and Peking University, Beijing, analyzed data from almost half a million Chinese adults in the China Kadoorie Biobank.

All the study participants were asked about their cooking habits by questionnaire, then tracked for hospital admissions of major eye diseases through linkage to health insurance records. Over the 10-year follow-up period, there were 4,877 cases of conjunctiva disorders, 13,408 cataracts, 1,583 disorders of the sclera, cornea, iris and ciliary body (DSCIC), and 1,534 cases of glaucoma among study participants.

Compared with those who cooked using clean fuels (electricity or gas), solid fuel users tended to be older, female, rural residents, less educated, agricultural workers and regular smokers. After accounting for these factors properly, the results suggested that long-term use of solid fuels for cooking was associated with 32 per cent, 17 per cent, and 35 per cent higher risks of conjunctiva, cataracts, and DSCIC, respectively, compared with those who cooked using clean fuels.

There was little difference in risk between the different types of solid fuel used (for instance, coal versus wood).

There was no association between long-term use of solid fuels and an increased risk of glaucoma.

Individuals who switched from using solid to clean fuels for cooking had smaller higher risks (over those who had always used clean fuels) compared to those who did not switch. People who switched had 21 per cent, five per cent and 21 per cent higher risk for conjunctiva, cataracts, and DSCIC, respectively.

Dr. Peter Ka Hung Chan, research fellow in the Nuffield Department of Population Health, University of Oxford, and lead author of the study, explained these findings: ‘The increased risks may be caused by exposure to high levels of fine particulate matter (PM2.5) and carbon monoxide, which can damage the eye surface and cause inflammation.’

Burning wood also increases the risk of eye injury from sparks or wood dust. The investigators propose that the reason there was no association between solid fuel use and risk of glaucoma was because this disorder affects internal eye structures, which are less exposed to pollutants in the air.

Among individuals who used solid fuels for cooking, the study did not find significant difference in excess risk between those with and those without cookstove ventilation (such as a chimney).

In China, around 400 million people still used solid fuels for domestic purposes in 2018. Worldwide, the percentage of the global population relying on solid fuels for cooking has only decreased modestly since 2010, by 11 per cent. Most of these people live in low-income countries, particularly in Africa and Asia. This can make it difficult for those affected by eye disorders to access effective and affordable treatment.

“Our study adds yet another piece of evidence to support governmental efforts to facilitate fuel transition, and the general public should be informed about the potential risks of eye diseases, some of which are highly disabling, related to solid fuel use.” said Liming Li from Peking University and a senior author for the study.

Read the full study in PLOS Medicine.