Smoking and Diabetes: Risk, Blood Sugar Control, and Quitting

Smoking raises the risk of type 2 diabetes and makes diabetes harder to manage. Quitting helps both — but the first years after quitting need some care, for a reason most articles skip.

Smoking Increases Type 2 Diabetes Risk

The CDC says that if you smoke, you have a 30% to 40% higher risk of developing type 2 diabetes than people who don't smoke, and the more you smoke, the higher your risk. A meta-analysis of 25 studies covering 1.2 million people found a pooled risk ratio of 1.44 for smokers, 1.61 for heavy smokers (20 or more a day) and 1.23 for former smokers.

The authors of that meta-analysis call the link an association and say future research should establish whether it is causal — so it's fair to say smoking is strongly linked to diabetes, with a dose-response pattern, while the exact mechanisms are still being worked out.

The Mechanisms

The CDC describes several:

Nicotine raises blood sugar, and inflammation and nicotine both make it harder for your body to regulate blood sugar
Belly fat: people who smoke have a higher risk of belly fat, which raises diabetes risk even if they don't have overweight
Chemicals in smoke damage the body and cause inflammation

Nicotine also releases adrenaline-type hormones, which push blood sugar up — a leading pharmacology review notes nicotine reduces sensitivity to insulin and may aggravate or precipitate diabetes.

Smoking With Existing Diabetes

The CDC says that people with diabetes who smoke often need larger doses of insulin, and are more likely to have complications — and worse ones — than people with diabetes who don't smoke. Those complications include heart disease, kidney disease, vision loss and amputation.

If you have diabetes, stopping smoking is one of the most important things you can do. Tell your diabetes team you're quitting.

What Happens After Quitting: A Short-Term Rise in Risk

Here's something many quitters and their healthcare providers aren't prepared for. In a US cohort study, people who had just quit had a higher short-term risk of developing diabetes than never-smokers (hazard ratio 1.73) — higher than continuing smokers', and the extra risk was largely explained by weight gain. The authors conclude that quitting should be coupled with diabetes prevention and early detection.

This is not a reason to keep smoking — smoking damages the heart, lungs and blood vessels in ways weight gain doesn't, and in the Framingham study the heart benefit of quitting held despite weight gain. It is a reason to:

Ask your GP to check your blood sugar in the first year or two if you're at risk of diabetes
If you already have diabetes, check your glucose more often after quitting — your medication may need adjusting, and the CDC notes that smokers often need more insulin, so needs can change when you stop
Pay attention to weight after quitting with regular meals and activity

Long-Term Benefits of Quitting

For people with or at risk of diabetes:

Heart and blood vessels: the biggest win — excess heart disease risk halves somewhere between one year (NHS, WHO) and three to six years (CDC)
Diabetes risk: in the meta-analysis, former smokers had a lower risk than current smokers (RR 1.23 against never-smokers, compared with 1.44)
Complications: the CDC says people with diabetes who don't smoke have fewer and less severe complications

FAQ

Does smoking cause type 2 diabetes?

Smoking is strongly linked to it: the CDC puts the extra risk at 30–40%, higher the more you smoke, and a large meta-analysis found about 61% higher risk in people smoking 20 or more a day. The authors call it an association whose causes are still being studied.

Does quitting smoking affect blood sugar?

It can, in both directions. In the first years, diabetes risk can rise, largely with weight gain — so it's worth getting your blood sugar checked and watching your weight. Over the longer term, former smokers have lower risk than people who keep smoking.

Is smoking worse if you have diabetes?

Yes. The CDC says people with diabetes who smoke are more likely to have complications, and worse ones, and often need more insulin. Quitting is one of the most important things you can do — with your diabetes team in the loop.