Indoor air pollution is a massive public health problem across the world. That is because three billion people are thought to cook and heat their homes with open fires and simple stoves burning wood, animal dung, crop waste (known as biomass) and coal.

Breathing in fumes from cooking smoke kills 600,000 Africans each year, a policy think-tank called the Africa Progress Panel tweeted recently.

Could the number of deaths be that high?

Estimating deaths due to risk factors tricky

The Africa Progress Panel consists of a forum of 10 prominent people, including former UN secretary-general Kofi Annan and humanitarian and former first lady of Mozambique, Graça Machel. They aim to influence policy in Africa.

We asked the think-tank for the source of its claim, which is also repeated in an article on its website. We have not yet received a reply but will update this report if we do.

In general, estimating deaths due to risk factors such as air pollution is tricky, a professor of environmental epidemiology at the Swiss Tropical and Public Health Institute, Martin Roosli, told Africa Check.

This is because you cannot directly observe the numbers of deaths. When people die as a result of breathing in fumes from burning solid fuels, they usually die of breathing difficulties caused by acute and chronic respiratory diseases.

Deaths due to three lung diseases, in particular, are usually linked to burning solid fuels for cooking: acute lower respiratory infections in children under five, chronic obstructive pulmonary disease and lung cancer in people older than 30.

To determine the number of deaths that can be attributed to a risk factor, such as cooking smoke, researchers work out how many people are exposed to it. From previous studies, they would know what the relative risk is of dying from a disease caused by indoor air pollution.

The resulting fraction would be multiplied by the total number of deaths in a given country in a given year to get an estimate of the number of deaths due to the risk factor.

Actual deaths lower than estimates

The figures cited by African Progress Panel are most likely to have been collected by the Institute for Health Metrics and Evaluation (IHME), Roosli told Africa Check.

The IHME is an independent global health research centre at the University of Washington in the US. For 2015, their estimate of the number of deaths in the African Union region due to cooking using solid fuels is 624,469, but it could range from 487,157 to 758,487. This is based on survey data.

However, Roosli pointed out that the chronic diseases which kill those exposed to cooking smoke have many causes. Therefore an estimate of the number of deaths caused by it will be larger than the actual number of deaths.

Conclusion: The claim is mostly correct

Deaths attributed to cooking smoke are estimated rather than actually observed. This is because the diseases which kill people exposed to cooking smoke have many causes. The actual number of people dying because of it are therefore lower than the estimates.

That said, the most recent data we have shows that between about 490,000 to 760,000 Africans died due to inhaling cooking smoke in 2015.

Researched by Vinayak Bhardwaj, Africa Check