Increased risk of smoking-related illnesses in schizophrenia patients: A nationwide cohort study

Background: Schizophrenia patients smoke at three times the rate of the general population, and are more susceptible to smoking-related illnesses. The goal of the current study was to evaluate the cumulative probability of chronic obstructive pulmonary disease (COPD) and ischemic heart disease (IHD) following first documentation of smoking among schizophrenia patients as compared to smoking healthy controls. Methods: A nationally representative cohort study was designed to assess the odds and cumulative probability of COPD and IHD among individuals with schizophrenia (n = 10,502) and a matched-sample of smoking healthy controls (n = 10,502). Hierarchical logistic regressions and Kaplan-Meier regression models were used to compare odds and cumulative probabilities across the two groups. Results: After adjusting for clinical and demographic factors, smoking schizophrenia patients had a higher probability of receiving a diagnosis of COPD than smoking healthy controls (OR 2.14, 95%CI 1.51–3.01, p < 0.001). The probability of having COPD increased more rapidly in smoking schizophrenia patients, yet the opposite trajectory prevailed for IHD, showing a decreased cumulative probability in smoking schizophrenia patients compared to smoking healthy controls. Discussion: Schizophrenia has a unique contribution to the facilitation of COPD, which extends beyond the effect of smoking, or other clinical and demographic risk factors. Differential smoking patterns could potentially account for this effect. The differential pattern of IHD should be subjected to further research, as our results might indicate that schizophrenia patients are underdiagnosed with IHD, and may be even less diagnosed as a function of time and chronicity.