Low household income increases risks for chronic obstructive pulmonary disease in young population: a nationwide retrospective cohort study in South Korea

Background Low socioeconomic status is a risk factor for chronic obstructive pulmonary disease (COPD); however, the association between low household income and COPD in young populations remains unclear.Methods We screened individuals aged 20-39 years who underwent the national health examination between 2009 and 2012 using the Korean National Health Information Database, which was searched until December 2019. We identified 5 965 366 eligible individuals, and 13 296 had newly developed COPD based on health insurance claims. We evaluated household income levels based on the health insurance premiums, categorised them into quartiles and 'Medical aid' (the lowest 3% income group), and assessed the annual income status from the preceding 4 years. Multivariate Cox proportional hazard models were used to estimate the adjusted HR (aHR) of risk factors for COPD.Results In the Medical aid group, the incidence rate for developing COPD was 0.56/1000 person-years, with an aHR of 2.45 (95% CI 1.91 to 3.13) compared with that of the highest income quartile group. This association was prominent in consecutive recipients of Medical aid (aHR 2.37, 95% CI 1.80 to 3.11) compared with those who had never been Medical aid beneficiaries. Those who experienced a decline in household income between the previous (preceding 4 years) and baseline time points had an increased risk of developing COPD, regardless of previous income status.Conclusion Low household income was associated with an increased risk of developing COPD in the young population. This risk was augmented by sustained low income and declining income status.