September 1, 2022

expert reaction to conference abstract looking at people exposed to air pollution revealing greater effects on females than males

A conference abstract (not a published paper) presented at European Respiratory Society International Congress 2022 looks at sex-related differences in response to diesel exhaust.

Prof Kevin McConway, Emeritus Professor of Applied Statistics, The Open University, said:

“It’s very difficult to evaluate a piece of research like this on the basis of a press release and a brief abstract (summary) of what’s going to be presented at the conference. Conference papers will not generally have gone through the sort of detailed peer review process that would be done before publication in a good journal, so I can’t rely on peer review either.

“My main concern about this conference presentation is that the research involved very few people – just five males and five females. The researchers report that the changes in components of the blood appeared to be different in males and females. But it’s likely that the males and females differed in many other ways than just their sex and/or gender, so there’s no way of telling whether it is their sex that actually causes the difference, or some other characteristics that they have. If we had more detail on exactly what statistical analysis had been done, and on how consistent the blood changes were in males and in females, things might be a bit clearer. But we haven’t, because those sorts of detail haven’t been published yet.

“So at this stage we just can’t go beyond a conclusion that there might be a general difference between males and females in how their blood changes after exposure to diesel exhaust, which is all that the researchers claim. On the other hand, if the reason for the observed difference is something other than sex, there might not be a difference between men and women in general in these blood changes.

“Another relevant point is that the researchers (rightly) don’t go beyond pointing out that some of the proteins involved play a role in things like inflammation, blood clotting or heart disease. That doesn’t mean that the changes in these proteins in the ten participants are actually linked to bad health in the participants, in these respects or any other ways. The researchers don’t report that they made any measurements of the participants’ health, so any conclusions about adverse effects of pollution on health are very distant from what was actually done in this study.”

Dr Samuel Cai, Lecturer in Environmental Epidemiology, University of Leicester, said:

“It is hard to judge if this is good quality research at present as this is only a conference abstract – we need to see the full peer-reviewed paper before we can really judge the quality. The design of the study was well considered, and the study was led by a team that has established expertise and lab facilities in this particular research topic.

“The quote from the author in the press release “Professor Mookherjee explained: “These are preliminary findings, however they show that exposure to diesel exhaust has different effects in female bodies compared to male and that could indicate that air pollution is more dangerous for females than males.” is a bit of an over-interpretation as it would need a robust dataset to confirm that.  From a public health point of view, it is quite risky to say that ‘air pollution is more dangerous for females and males’, although one could say that these preliminary findings seem to suggest stronger impacts from DE in females than males.

“However, there are some limitations as I can see from the abstract, and I think these preliminary findings should be interpreted with greater caution. So, first of all, due to the nature or some practical reasons of the controlled human exposure study, the study sample is very small with only 10 healthy non-smokers. Therefore, it will be extremely difficult to generalise these findings to a broader population group. Second, this study design typically only assessed short-term, rather than long-term air pollution impacts, it is therefore unclear how the exposure may eventually lead to the development of chronic diseases such as asthma. Third, as this is a controlled human exposure study, it may not be able to capture the full picture of real-world exposure.

“We all know that air pollution is a risk factor for many respiratory diseases, and many of the respiratory diseases tend to have sex differences in terms of disease incidence, treatment responses and mortality. Most, but not all, population-based studies in adults did find that the associations between air pollution and respiratory diseases tend to be stronger in females than males. So, this study does provide some mechanistic insights into it.

“Confounders adjustment is possibly not a big issue in this study design – in terms of limitations, I mentioned a few above. As this study only involved 10 healthy non-smokers males and females, it is unknown about the impact of sex-differences on the DE impacts on people with long-term respiratory health conditions such as asthma and COPD, further research is needed to better clarify susceptibility in different sub-groups of the populations, and that will help aid clinical decisions on the management of these respiratory disease patients.

“As these findings are still preliminary, I don’t think there are some real implications. Sex- and gender differences in air pollution and health studies are really complex, as they involve many different aspects in terms of behavioural, occupational, physiological and psychological differences between the two sexes. Whether the impacts are stronger in a given sex really depends on the types of air pollutants, studied health outcomes and the study population, so I would not over speculate at this stage.”

Abstract title: “Plasma proteomics analysis reveals sex-related differences in response to diesel exhaust”, by Mahadevappa Hemshekhar et al; Presented in session, “Impact of the external and internal exposome on chronic lung disease” at 08:30-09:30 CEST on Sunday 4 September 2022 at the European Respiratory Society International Congress 2022

There is no paper.

Declared interests

Prof Kevin McConway: “I am a Trustee of the SMC and a member of its Advisory Committee.  My quote above is in my capacity as an independent professional statistician.”

Dr Samuel Cai: “I have no conflict of interest.”