Study Finds Lower COPD Risk Among Patients Living in Cities With Fewer Than 50,000 Residents

Individuals living in cities with fewer than 50,000 residents had a lower risk of developing chronic obstructive pulmonary disease (COPD) than those living in cities with 50,000 residents or more, according to a study published in BMC Public Health.¹

Although most people in the Western world spend most of their time indoors, limited information is known about the relationship between indoor environments and COPD. Past studies found that housing conditions and indoor environments are associated with COPD exacerbations.² Similarly, past research determined that older dwellings, mold, and home ownership are associated with respiratory symptoms.^3-5

However, less is known regarding the relationships between indoor environments and housing conditions with developing COPD.¹ Consequently, the researchers conducted a study to explore these relationships.

A Danish study found that living in cities with fewer than 50,000 residents and in newer, owned, and less dense homes is associated with a lower risk of developing chronic obstructive pulmonary disease (COPD). | Image Credit: leungchopan - stock.adobe.com

The researchers used data from the Danish Civil Registration System, the Health and Morbidity Survey Year 2000 (DHMS 2000), the Danish Prescription Register, and the Danish National Patient Register. The DHMS 2000 received 16,688 responses from participants 16 years and older, corresponding to a 74.2% response rate. Each respondent completed an interview with questions about various topics, including their health, indoor environment, and demographics.

Then, the researchers linked each participant from the DHMS 2000 to the Danish National Health and Administrative registers using their unique, permanent identification number assigned at birth or immigration. Of the respondents, they analyzed those 30 years and older who were free of COPD 10 years before the date of their interview; COPD was diagnosed based on register-based information.

Information about urbanization, construction period, and resident density was obtained by linkage to the Building and Housing Register and the Danish Civil Registration System. Additionally, the researchers obtained information about the patients’ housing type and self-reported indoor environment from the questionnaire.

The study population consisted of 11,590 patients, their ages ranging from 30 to 98, with the median age being 51.4 years (IQR, 40.7-62.8). Of the included patients, 49.4% were men, and most lived in owned homes (71.5%). Also, 23.8% of patients lived in cities with 50,000 or more residents, while 17.6% lived in rural areas with less than 200 residents.

At inclusion, patients lived in their residences for a median of 10.1 years (IQR, 3.8-21.6); the median follow-up time was 9.9 years (IQR, 3.5-18.3). The researchers reported that from 2000 to 2018, 1033 patients (8.6%) were diagnosed with COPD, corresponding to an overall COPD incidence rate (IR) of 8.6 per 1000 person-years.

The COPD IR was 17% lower among patients living in homes built after 1982 than those living in homes built before 1962; however, this is only borderline significant (incidence rate ratio [IRR], 0.83; 95% CI, 0.68-1.03). Also, patients in rented homes had a higher COPD risk than those living in owned homes (IRR, 1.47; 95% CI, 1.27-1.70). As for resident density, patients in more dense households had a higher COPD risk than those in less dense households (IRR, 1.15; 95% CI, 0.92-1.45).

Additionally, the COPD IR was lower among patients living outside big cities compared to those living in cities with 50,000 residents or more. More specifically, the IRs were 23%, 21%, and 14% for patients living in cities with 200 to 4999 residents, in rural areas, and in cities with 5000 to 49,999 residents, respectively; this finding was not statistically significant among patients in cities with 5000 to 49,999 residents.

Lastly, patients living in semi-detached houses had a higher COPD risk than those living in detached houses (IRR, 1.29; 95% CI, 1.08-1.55). Conversely, there was no risk difference among patients with different perceived indoor environments. Overall, the researchers discovered similar patterns when stratified by smoking status except for the perceived indoor environment, where opposite patterns existed for smokers and nonsmokers.

The researchers acknowledged their limitations, one being that they only analyzed Danish patients, so their findings may not be generalizable to other populations. Also, they did not have any information regarding occupational exposure to smoke or dust, which is a known COPD risk factor. Despite these limitations, the researchers suggested areas for further research based on their findings.

“All studied exposures in the current study are to some degree interrelated or on the same causal path between housing conditions and COPD,” the authors wrote. “Mediation analyses that can help disentangle the contribution of each factor to the overall risk is of importance in future research.”

References

1. Kloster S, Kirkegaard AM, Davidsen M, et al. Housing conditions and risk of incident COPD: a Danish cohort study, 2000-2018. BMC Public Health. 2024;24(1):1714. Published 2024 Jun 27. doi:10.1186/s12889-024-19131-3
2. Decramer M, Janssens W, Miravitlles M. Chronic obstructive pulmonary disease. Lancet. 2012;379(9823):1341-1351. doi:10.1016/S0140-6736(11)60968-9
3. Wang J, Janson C, Jogi R, et al. A prospective study on the role of smoking, environmental tobacco smoke, indoor painting and living in old or new buildings on asthma, rhinitis and respiratory symptoms. Environ Res. 2021;192:110269. doi:10.1016/j.envres.2020.110269
4. Shaw M. Housing and public health. Annu Rev Public Health. 2004;25:397-418. doi:10.1146/annurev.publhealth.25.101802.123036
5. Mendell MJ, Macher JM, Kumagai K. Measured moisture in buildings and adverse health effects: a review. Indoor Air. 2018;28(4):488-499. doi:10.1111/ina.12464