Aim We examined associations between smoking and HbA1c among U.S. adults, and whether these associations vary by diabetes status.

Methods We analyzed NHANES data from 2015–2018 for adults aged ≥20 years. Smoking was assessed by self-report and serum cotinine. Survey-weighted multivariable linear regression was used to evaluate the association between smoking and HbA1c in the full population (N=9,214) and in adults without diabetes (N=7,328), adjusting for demographics, blood pressure, waist circumference, lipids, and C-reactive protein.

Results After adjustment for cardiometabolic covariates, there was no significant association between smoking and HbA1c in the full population (former: β=0.029%, p=0.30; current: β=0.053%, p=0.13). Among adults without diabetes, former smoking was not associated with HbA1c, whereas current smoking remained significantly associated (former: β=−0.001%, p=0.923; current: β=0.067%, p<0.001). These findings were similar when cotinine was used as the exposure measure, with active smoking (≥3.0 ng/mL) associated with higher HbA1c among non-diabetic adults (p<0.001), but not in the full population.

Conclusions Among adults without diabetes, current but not former smoking was associated with higher HbA1c. The absence of an association in former smokers suggests that this effect may attenuate following cessation. These findings support early cessation interventions and may inform cessation counseling and diabetes screening.

The authors have declared no competing interest.

The author(s) received no specific funding for this work.

I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained.

Yes

The details of the IRB/oversight body that provided approval or exemption for the research described are given below:

NHANES protocols were approved by the National Center for Health Statistics Research Ethics Review Board. Every participant also provided informed consent before their data were collected. We did not require any further ethics approval, as the data are publicly available and do not contain any identifiable information.

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Data are publicly available from the National Health and Nutrition Examination Survey (NHANES) conducted by the Centers for Disease Control and Prevention (CDC). The specific datasets analyzed in this study are from the NHANES 2015-2016 and 2017-2018 continuous cycles and can be accessed at https://www.cdc.gov/nchs/nhanes/index.htm. No special permissions are required to access these data.