A review looks at passive smoking as a risk factor for dementia and cognitive impairment

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Researchers from the Centre for Dementia Prevention have published a systematic review paper on the links between passive smoking and dementia. They reviewed research from nine different articles and overall found some weak evidence that passive smoking increases the risk of dementia or cognitive impairment.
There has been relatively little research into passive smoking and dementia. The review, led by Dr Lucy Stirland (pictured), aimed to find and summarise all the existing evidence currently available. The quality of each published article was also assessed to give an indication of how reliable the findings from each article are.

The search found nine relevant papers from four different countries. The papers compared people who were exposed to passive smoke with those who were not. Most of the studies found that people exposed to passive smoke scored less well on cognitive testing. Some of the papers looked specifically at dementia diagnoses and found these more common in people exposed to passive smoke. However, other papers did not find convincing evidence of either of these links.

In reviews of this type, the quality of research is assessed based on the way each study was conducted. The papers in this review varied, with two of excellent design and others having some shortcomings.

The overall conclusion was that passive smoking may increase the risk of dementia, but that this finding is relatively weak. The evidence is further limited by the majority of the research being of medium or low quality.

As there are few treatments available for dementia, it is important to identify risk factors that are potentially avoidable. It is well established that smoking increases the risk of dementia, but less work has been done on passive smoking. This review article may be useful to other researchers examining environmental risk factors for dementia. It also adds to what is known about the secondary harms of smoking, which is relevant to those involved in smoking legislation.

Stirland, L., O’Shea, C., & Russ, T. (2017). Passive smoking as a risk factor for dementia and cognitive impairment: Systematic review of observational studies. International Psychogeriatrics, 1-11