Asthma is usually thought of as a disease of the lungs, causing symptoms such as wheezing, coughing, chest tightness, and difficulty breathing. But researchers are increasingly investigating whether chronic inflammation associated with the condition could also affect the brain.

A 2023 study published in Brain Communications found that asthma was associated with changes in the brain's white and grey matter, as well as stronger links between markers of Alzheimer's disease pathology and cognitive decline. The findings suggest that the effects of asthma may extend beyond the airways, although they do not prove that asthma causes dementia.

What Did the Study Find?

Researchers analysed data from 217 adults aged 45 to 90. Of these, 31 had asthma, while 186 did not have asthma or other chronic respiratory diseases. About 62% of participants were women, and 92.2% were cognitively unimpaired at the time of the study. The group was also enriched for people with a parental history of Alzheimer's disease, meaning the findings may not apply equally to the general population.

The researchers used advanced diffusion MRI to examine the microscopic structure of white and grey matter in the brain. They also analysed cerebrospinal fluid for biomarkers associated with Alzheimer's disease, neuroinflammation, glial activation and neurodegeneration.

They found that, among people with asthma, Alzheimer's-related biomarkers were more strongly associated with unfavourable changes in white matter. These included lower levels of amyloid-beta 42 relative to amyloid-beta 40 and higher levels of phosphorylated tau-181, both of which are associated with Alzheimer's disease pathology.

The study also found that age-related deterioration in white matter was more pronounced among participants with asthma.

Asthma and Cognitive Decline

Perhaps most importantly, changes in the brain's white and grey matter were more strongly associated with cognitive decline in people with asthma than in those without the condition.

This does not mean that having asthma will cause dementia. Instead, the findings suggest that asthma may amplify the relationship between underlying brain pathology, structural changes, and declining cognitive performance.

The researchers said chronic inflammation could be one factor connecting respiratory disease and brain health. Previous research has also suggested a potential 'lung-brain axis', through which changes in the respiratory system and systemic inflammation may influence brain structure and function.

Should People With Asthma Be Worried?

Maybe not. The study had several important limitations. Only 31 participants had asthma, making the asthma group relatively small. The researchers also could not assess whether asthma severity changed the relationship because of the limited sample size. Asthma status was determined using prescription information rather than relying solely on a physician-confirmed diagnosis.

Most importantly, the research was observational. It identified associations between asthma, brain changes, and cognitive decline but cannot establish that asthma directly caused those changes. The participants also had a higher-than-usual risk of Alzheimer's disease because many had a parental history of the condition.

Still, the findings add to the evidence that controlling chronic inflammatory conditions may be important for overall health, potentially including brain health. The researchers suggested that effective asthma management could potentially help slow cognitive symptoms, although this possibility needs to be tested in future studies.

For people living with asthma, the practical takeaway remains straightforward: keeping the condition under control is important not only for breathing but potentially for long-term health more broadly.

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