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NHANES observational review links current smoking to higher HbA1c in non-diabetic adultsSmoking Raises Blood Sugar in People Without Diabetes

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Key Takeaway
Consider that current smoking is associated with higher HbA1c in non-diabetic adults, but causality cannot be inferred from this observational data.

This is an observational analysis of NHANES 2015-2018 data, examining the association between smoking status and HbA1c in U.S. adults. The study included N=9,214 full population participants and N=7,328 adults without diabetes.

In the full population, after adjustment for cardiometabolic covariates, no significant association was found between smoking and HbA1c. For former smokers, the effect size was β=0.029% (p=0.30); for current smokers, β=0.053% (p=0.13). Among adults without diabetes, current smoking was significantly associated with higher HbA1c (β=0.067%, p<0.001), while former smoking was not (β=-0.001%, p=0.923). Using serum cotinine, active smoking (≥3.0 ng/mL) was associated with higher HbA1c in non-diabetic adults (p<0.001), but not in the full population.

The authors note key limitations: the observational design cannot establish causality, self-reported smoking may have recall bias, and NHANES data may not be generalizable to all populations. No adverse events or follow-up duration were reported.

Practice relevance is restrained; the findings support early cessation interventions and may inform counseling, but causality cannot be inferred. The analysis is based on adjusted regression models, with uncertainty preserved as reported.

Imagine you light up a cigarette. You might think about your lungs or your heart. But what about your blood sugar? A new study suggests that smoking affects blood sugar levels even in people who don’t have diabetes. This is a hidden risk that many smokers never consider.

Diabetes is a serious health problem. It affects millions of adults in the United States. High blood sugar can damage your eyes, kidneys, and nerves over time. Many people think diabetes only comes from diet or genetics. But this study shows that smoking plays a role too.

Even if you don’t have diabetes, high blood sugar can be a warning sign. It is called prediabetes. This condition puts you at higher risk for developing full diabetes later. Finding ways to lower blood sugar early is key to staying healthy.

The Surprising Shift

For years, doctors have known smoking is bad for the heart and lungs. But the link to blood sugar was less clear. Some older studies were mixed. They did not always separate people with diabetes from those without it.

This new research looked at a large group of adults. It found a clear pattern. Current smoking was linked to higher blood sugar in people without diabetes. But former smokers did not have this link. This suggests that quitting smoking can reverse the effect on blood sugar.

Think of your body like a car engine. Blood sugar is the fuel. Insulin is the key that lets fuel into the engine. When the key works well, the engine runs smoothly.

Smoking can make the key rusty. It causes inflammation and stress in the body. This makes it harder for insulin to do its job. As a result, sugar builds up in the blood.

But here is the good news. When you stop smoking, the body starts to heal. The inflammation goes down. The insulin key works better again. This is why former smokers in the study did not have higher blood sugar.

Researchers used data from a large national survey called NHANES. They looked at over 9,000 adults aged 20 and older. The data came from 2015 to 2018.

They measured smoking in two ways. One was by asking people if they smoked. The other was by testing blood for cotinine, a chemical from tobacco. They also checked blood sugar levels using a test called HbA1c.

After adjusting for age, weight, and other health factors, the results were clear. In the full group of adults, smoking did not seem to link to higher blood sugar. But when they looked only at people without diabetes, the story changed.

Current smoking was linked to higher blood sugar in non-diabetic adults. Former smokers did not show this link. The same results appeared when using the blood test for cotinine.

This means that active smoking raises blood sugar. But once you quit, the risk drops. This is a strong reason to stop smoking now.

But There’s a Catch

This study shows a link, but it does not prove smoking causes diabetes. It is possible that other factors play a role. For example, people who smoke might have different habits or diets. The study tried to adjust for these, but it is not perfect.

This study adds to the evidence that smoking harms more than just the lungs. It supports early efforts to help people quit smoking. Doctors can use this information to talk to patients about diabetes risk. Even if you don’t have diabetes, quitting smoking can help protect your future health.

If you smoke, this is a sign to consider quitting. Talk to your doctor about ways to stop. There are many tools available, like patches, gum, or counseling. Quitting can lower your risk for many diseases, including diabetes.

If you don’t smoke, keep up the good work. Avoiding tobacco is one of the best things you can do for your health.

This study was based on a survey. It cannot prove cause and effect. It only shows a link. Also, the data is from a few years ago. Smoking habits and health can change over time. More research is needed to confirm these findings.

Researchers will continue to study how smoking affects blood sugar. Future studies might look at how long it takes for blood sugar to improve after quitting. For now, this study gives a clear message: quitting smoking helps your blood sugar, even if you don’t have diabetes.

Study Details

Sample sizen = 9,214
EvidenceLevel 5
PublishedApr 2026
View Original Abstract ↓
AimWe examined associations between smoking and HbA1c among U.S. adults, and whether these associations vary by diabetes status. MethodsWe analyzed NHANES data from 2015-2018 for adults aged [&ge;]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. ResultsAfter adjustment for cardiometabolic covariates, there was no significant association between smoking and HbA1c in the full population (former: {beta}=0.029%, p=0.30; current: {beta}=0.053%, p=0.13). Among adults without diabetes, former smoking was not associated with HbA1c, whereas current smoking remained significantly associated (former: {beta}=-0.001%, p=0.923; current: {beta}=0.067%, p<0.001). These findings were similar when cotinine was used as the exposure measure, with active smoking ([&ge;]3.0 ng/mL) associated with higher HbA1c among non-diabetic adults (p<0.001), but not in the full population. ConclusionsAmong 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.
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