The Effects of Smoking on Glycemic Control and Microvascular Complications in Type 1 Diabetes
Open AccessBackground: Several studies have demonstrated the significant effects of smoking on the risk of microvascular complications, however, few have also examined the mediating effects of HbA1c. Using publicly available data from the well-characterized cohort of 1,441 subjects with type 1 diabetes who participated in the Diabetes Control and Complications Trial (DCCT), we describe the acute and long-term risks of smoking on glycemic control and microvascular complications (retinopathy and nephropathy). Research Design and Methods: Over a mean of 6.5 years of follow-up, the DCCT recorded self-reported smoking behaviors, glycemic exposure based on HbA1c values, and complications status. Generalized linear mixed models were used to assess whether time-dependent measurements of smoking predict HbA1c levels. Cox proportional hazard models were used to assess time-dependent smoking exposures as predictors of retinopathy and nephropathy. All models were adjusted for potential baseline confounders.Results: During the DCCT, current smokers had consistently higher HbA1c values compared with former and never smokers (0.35% mean difference vs. never smokers; 0.29% mean difference vs. former smokers). The quantitative smoking exposures summarized over the period of the DCCT were also predictive of HbA1c. HbA1c increased by 0.14-0.16 for every 5-unit increase in DCCT total duration and DCCT total pack-years. Additionally, current smokers had a 42% higher risk of retinopathy and 34% higher risk of nephropathy compared with never smokers. The quantitative smoking exposures had a minimal effect on the risk of complications compared with the relative effect of the smoking status variables. The significant associations between smoking and complications were fully attenuated after adjusting for HbA1c. Former smokers did not differ significantly from never smokers with respect to HbA1c and the risk of complications. Conclusions: Smoking is associated with poor glycemic control and an increased risk of microvascular complications in individuals with type 1 diabetes. Our data suggests that the negative effects of smoking on glycemic control may be a mechanism by which smoking leads to complications of type 1 diabetes. The harmful effects of smoking on HbA1c and the risk of complications may not persist after quitting smoking.
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Braffett_gwu_0075A_11763.pdf | 2018-01-16 | Open Access |
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