Ever-Smokers With COPD Have a Greater Risk of Developing ADHD, Study Says

Ever-smokers with chronic obstructive pulmonary disease (COPD) have a greater risk of developing attention-deficit/hyperactivity disorder (ADHD), according to a study published in the International Journal of Chronic Obstructive Pulmonary Disease.

The researchers explained that previous studies reported a higher prevalence of depression and anxiety in patients with COPD compared with the general population. Similarly, several studies found an association between COPD and cognitive impairment. To explore the association between COPD and mental illnesses, the researchers used a 2-sample Mendelian randomization (MR); they also conducted subgroup analyses based on smoking history.

They noted that MR is used to investigate causal relationships between exposures and outcomes of interest. It achieves this by utilizing single nucleotide polymorphisms (SNPs) as unbiased proxies for exposures. The researchers explained that this approach helps address challenges associated with residual confounding and reverse causality frequently encountered in conventional observational studies.

Man smoking | Image Credit: ehabeljean - stock.adobe.com

“Given the complexity of COPD’s pathogenesis and numerous confounding factors, conducting MR studies is essential to establish whether a causal relationship exists between COPD and psychiatric disorders at the genetic level,” the authors wrote.

To conduct their study, the researchers used data on patients with COPD sourced from the Genetic Alliance’s publicly accessible repository of statistical data obtained from genome-wide association studies (GWAS). Based on their smoking histories, the researchers categorized the patients into 1 of 2 groups: ever-smokers with COPD or never-smokers with COPD. Also, data on common psychiatric disorders, like ADHD, Alzheimer disease, anxiety disorder, and major depressive disorder (MDD), were obtained from the Psychiatric Genomics Consortium.

Overall, the researchers did not identify a causal link between COPD and the development of common psychiatric disorders. Through their subgroup analyses, they also did not identify a significant association between never-smoking patients with COPD and psychiatric disorders.

Conversely, the researchers identified a significant association between ever-smokers with COPD and an increased ADHD risk (OR, 2.303; 95% CI, 1.558-3.403; P = .001). Additionally, they identified a significant association between ever-smokers with COPD and a modestly reduced Alzheimer disease risk (OR, 0.994; 95% CI, 0.988-0.999; P = .034); no other significant correlations were observed between ever-smokers with COPD and psychiatric disorders.

Despite these findings, the researchers noted a continued debate about the association between COPD and cognitive decline, as it remains unclear whether the decrease in lung function or the shared risk factor of smoking plays a predominant role. This is because smoking exerts a more substantial influence on the initiation and progression of both COPD and Alzheimer disease; tobacco smoke induces oxidative stress that affects normal brain tissue functioning. Consequently, they explained that quitting smoking after a COPD diagnosis may protect against the development of Alzheimer disease in former smokers.

The researchers also acknowledged their study’s limitations, one being that the sample population was restricted to individuals of European descent. Because of this, caution must be exercised when generalizing these findings to broader populations. Despite any limitations, the researchers made future suggestions based on their findings.

“…attention needs to be paid to preventing psychiatric disorders in COPD patients with a smoking history,” the authors concluded.

Reference

Zhang Q, Zhang H, Xu Q. Association of chronic obstructive pulmonary disease with risk of psychiatric disorders: a two-sample Mendelian randomization study. Int J Chron Obstruct Pulmon Dis. 2024;19:343-351. doi:10.2147/COPD.S442725