Hofer et al. (1) report on smoking and metabolic control in a large study that combines type 1 diabetes registries from Europe and the U.S., with a total of more than 20,000 patients.
Smokers were found to have higher HbA1c (8.5% vs. 7.9% [70 vs. 62 mmol/mol]); we presume this is in comparison with those who were not current smokers. These HbA1c concentrations were adjusted for age-group, sex, duration of type 1 diabetes, and migration background/not non-Hispanic white. Although the percentage of smokers was higher in Europe than in the U.S., there were more ex-smokers in the U.S. The authors do not present the mean HbA1c for the two continents separately, nor the relationship between values for smokers versus ex-smokers, and doing so would add value to their results.
We have published a meta-analysis with individual data on more than 35,000 people who were not treated with glucose-lowering agents (2). We found that, in comparison with those who had never smoked, HbA1c was higher by 0.10% (95% CI 0.08, 0.12) (1.1 mmol/mol [0.9, 1.3]) in current smokers and higher by 0.03% (0.01, 0.05) (0.3 mmol/mol [0.1, 0.5]) in ex-smokers. This relation remained consistent across sex, age, and BMI strata. In contrast, there was little difference in fasting plasma glucose for current smokers compared with never-smokers (−0.004 mmol/L [−0.06, 0.02]), but for ex-smokers fasting plasma glucose was higher by 0.12 mmol/L (0.09, 0.14).
We question whether HbA1c should be used alone to evaluate glycemic control in people with type 1 diabetes, particularly in those who smoke, as smoking may alter HbA1c independent of glycemia. A continuous glucose monitoring study is required to compare the glucose profiles according to smoking habits in people with type 1 diabetes.
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Duality of Interest. No potential conflicts of interest relevant to this article were reported.
