Impact of smoking on diabetes complications: a secondary analysis of the Korean National Health Insurance Service-health screening cohort (2002– 2019)

Purpose: This study aimed to examine the effects of smoking on the incidence of macrovascular and microvascular complications in patients with type 2 diabetes. Methods: We analyzed 35,804 patients diagnosed with type 2 diabetes between 2004 and 2017 using the Korean National Health Insurance Service–National Health Screening Cohort (2002–2019). Smoking status was categorized into never, former, and current smokers, with further classification based on duration of smoking and daily smoking amount. We conducted survival analysis using a Cox proportional hazards model. Results: Both former and current smokers had significantly elevated risks of macrovascular complications compared to non-smokers, with hazard ratios (HRs) of 1.60 (95% confidence interval [CI], 1.49– 1.66) and 1.10 (95% CI, 1.08–1.17), respectively. Long-term smokers (over 30 years) had significantly higher risks of both macrovascular (HR, 1.35; 95% CI, 1.29–1.42) and microvascular complications (HR, 1.36; 95% CI, 1.30–1.42). Heavy smokers (over 2 packs/day) had a higher risk of developing macrovas-cular (HR, 1.46; 95% CI, 1.30–1.64) and microvascular (HR, 1.78; 95% CI, 1.60–1.98) complications than never smokers. Notably, former smokers had increased risks of developing neuropathy (HR, 1.40; 95% CI, 1.31–1.49), nephropathy (HR, 1.27; 95% CI, 1.16–1.39), and retinopathy (HR, 1.49; 95% CI, 1.39–1.60). Conclusion: Patients with type 2 diabetes and a history of smoking are at higher risk of developing mac-rovascular and microvascular complications. Smoking cessation, along with reducing smoking duration and amount, is crucial for lowering these risks.