Middle-age adults with reduced respiratory function have up to a 27% higher risk of developing dementia or cognitive impairment later in life, a study suggests.
This risk pattern is even more pronounced in patients with restrictive lung diseases such as idiopathic pulmonary fibrosis (IPF), according to the study, titled “Impaired Lung Function, Lung Disease, and Risk of Incident Dementia,” published in the American Journal of Respiratory and Critical Care Medicine.
The high prevalence of dementia and mild cognitive impairment has brought these conditions to the spotlight, and finding potential modifiable risk factors that contribute to their development is very important from a societal point of view.
Previous studies have suggested that lung diseases, such as chronic obstructive pulmonary disease (COPD), chronic bronchitis, and asthma, could be linked to a higher risk of dementia or worsening cognitive ability.
But it is not fully clear how these conditions are interconnected. Researchers believe that inflammation, oxidative stress (an imbalance between harmful free radicals and antioxidants), and abnormal tissue oxygenation induced by lung disorders could have a major role.
“Preventing dementia is a public health priority, and previous studies have suggested that poor lung health, which is often preventable, may be linked to a greater risk of developing dementia,” Pamela L. Lutsey, MD, PhD, epidemiologist at the University of Minnesota’s School of Public Health and lead study author, said in a press release.
“In this study, we looked at the long-term association between poor lung function and the risk of developing dementia, using high-quality measures,” she said.
The study, called ARIC (NCT00005131), enrolled 15,792 individuals, with a mean age of 54.2 years, across four U.S. communities — suburbs of Minneapolis, Minnesota; Jackson, Mississippi; Forsyth County, North Carolina; and Washington County, Maryland — who were followed for an average of 23 years.
For the purpose of this particular analysis, the team evaluated the clinical records of 14,184 individuals, of whom 17.6% were classified as having COPD, 5.9% had restrictive lung impairment, 33.5% showed respiratory symptoms with normal lung function results, and 43.1% were considered to have healthy lungs.
A total of 1,407 cases of dementia were reported during the 23-year follow-up period.
A detailed analysis revealed that participants who had restrictive lung impairment (including those with IPF) had a 58% higher risk for dementia or mild cognitive impairment, than those who had healthy respiratory function. The group of patients with COPD (obstructive disease) was found to have a 33% higher risk of these neurological conditions.
These results were found to be similar between smokers and non-smokers.
Overall, patients with more severely affected lung function, as determined by the lowest values of forced expiratory volume in one second (FEV1) and forced vital capacity (FVC), were found to have a 25-27% higher risk of dementia or cognitive impairment.
“Though both the COPD and restrictive impairment patterns tended to be associated with greater dementia and mild cognitive impairment risk, the magnitude of association was generally stronger for the restrictive impairment pattern,” the researchers wrote. Of note, IPF has a restrictive impairment pattern.
Additionally, these findings suggest that “suboptimal lung health may be related to dementia or mild cognitive impairment risk through both Alzheimer’s disease and cerebrovascular etiologies,” they added.
According to the team, the results of this large-scale study suggest that prevention of these lung diseases, in particular restrictive lung impairment disorders, may help reduce the incidence and burden of dementia and cognitive impairment.
“If other studies confirm our study’s findings, both individuals and policymakers will have an added incentive to make changes that protect lung health, as doing so may also prevent dementia,” Lutsey said.