Changes in smoking status, amount of smoking and their relation to the risk of microvascular complications in men with diabetes mellitus

Background: Smoking is a definite risk factor for macrovascular complications in diabetes mellitus (DM). However, the effect of smoking on microvascular complications is inconclusive. Method: Study participants were 26,673 diabetic men who received health check-up both in 2003–2004 and 2009, excluding women. Assessing smoking status (never, quitting and current) at 2003–2004 and 2009, changes in smoking status were categorised into 7 groups (never - never, never - quitting, never - current, quitting—quitting, quitting—current, current—quitting and current—current). Smoking amount was categorised into never, light (0–10 pack years), moderate (10–20 pack years), and heavy smoking (>20 pack years) based on 2009 data. They were followed-up until 2013 to identify incident microvascular complications. We calculated the adjusted hazard ratios (HR) and 95% confidence interval (CI) (adjusted HR [95% CI]) for incident microvascular complications according to changes in smoking status and smoking amount. Results: Current-quitting (1.271 [1.050–1.538]), current-current (1.243 [1.070–1.444]) and heavy smoking (1.238 [1.078–1.422]) were associated with an increased risk of overall microvascular complications. The risk of nephropathy increased in current-current smoking (1.429 [1.098–1.860]) and heavy smoking (1.357 [1.061–1.734]). An increased risk of neuropathy was observed in current-quitting smoking (1.360 [1.076–1.719]), current-current smoking (1.237 [1.025–1.492]) and heavy smoking (1.246 [1.048–1.481]). However, we couldn’t see the interpretable findings for the association between smoking and retinopathy. Conclusions: Lasting and heavy smoking increases the risk of microvascular complications, including nephropathy and neuropathy. Quitting smoking and reducing smoking amount are imperative in preventing microvascular complications in DM patients.