February 10, 2023

expert reaction to study on association of long term exposure to air pollution and depression in later life

A study published in JAMA Network Open looks at long-term exposure to air pollution and late-life depression in older adults in the US.

Prof Oliver Robinson, Professor of Neuroscience and Mental Health, University College London (UCL), said:

Is this good quality research?  Are the conclusions backed up by solid data?

“This is a comprehensive dataset with the sort of large sample needed to identify these patterns. They have access to, and can control for, a large range of relevant confounders. There are three pollutants measured and the patterns are similar across all three (i.e. that exposure to pollutants increases incidence of late-life depression) which provides increased confidence in the findings.

How does this work fit with the existing evidence?

“We know lots of environmental factors contribute to mental ill health, this adds to that clear picture (including from a recent ‘meta analysis’ from the same authors which pooled all evidence available on the link between pollution and mental health before this study). It is also consistent with experimental work in animal models (in which, unlike in humans, it is possible to do controlled pollutant exposure studies).

Have the authors accounted for confounders?  Are there important limitations to be aware of?

“The authors adjust for many relevant confounders and also show that the effects are greater in those who are more vulnerable due to being older, having other comorbid illnesses, or being socioeconomically disadvantaged. One thing to consider is that this is an American sample, and the average levels of pollution may be much lower than places like London. Even though the researchers control for factors such as socio-economic status, poverty and psychosocial stress it is hard to fully disentangle these measures which are in turn also linked to depression. Finally, as with any sample from a specific program (in this case Medicare) there are likely biases in those who end up in the sample due to biases in enrolment.

What are the implications in the real world?  Is there any overspeculation?  How do these air pollution levels compare to the UK?

“This adds to a growing picture that we should be concerned about the effects of pollution on mental health on top of the more obvious links to respiratory health.

“This work has implications for places like London because the median NO2 exposure in this study is 15.4 but for example, in the Tower Hamlets areas which is currently discussing pollution exposure policies (https://talk.towerhamlets.gov.uk/lsbethnalgreen), on the equivalent average data is currently double this at 33.7 (https://talk.towerhamlets.gov.uk/4093/widgets/12671/documents/37041; n.b., measurement units not provided in the document) which is at the most extreme end of this studies’ data and would mean there is a substantially greater exposure and risk in London. As a result this study might not be representative outside of the US in areas where pollutant levels are much higher. 

Is there any proposed mechanism of action for this association? How would this be studied and tested?

“The proposed mechanism is through inflammation. It has been shown in both human and animal studies that these sorts of pollutants can increase inflammation and there is a strongly emerging link between inflammation and depression (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2680424/). As with all aspects of mental health there is a complex relationship between individual vulnerability and resilience and the environmental exposure, so it is not that everyone who is exposed to these pollutants will go on to develop depression, but this is a plausible mechanism. It would be ideal to replicate this analysis with comparable NHS datasets to identify the comparable relationships in the UK.”

‘Association of Long-term Exposure to Air Pollution With Late-Life Depression in Older Adults in the US’ by Xinye Qiu et al. was published in JAMA Network Open at 16:00 UK time on Friday 10^th February.

DOI: 10.1001/jamanetworkopen.2022.53668 (Reprinted)

Declared interests

Prof Oliver Robinson: “Live and work in London. Salary support from Medical Research Council. Consulting for Roche, Blackthorn therapeutics and Peak. Investigator Initiated Trial with Lundbeck. Ethics panel for IESO.”