Smoking is a health hazard for anyone, but for people with diabetes or a high risk of developing the disease, lighting up can contribute to serious health complications.

Researchers have long known that diabetes patients who smoke have higher blood sugar levels, making their disease more difficult to control and putting them at greater danger of developing complications such as blindness, nerve damage, kidney failure and heart problems. Now a new study offers the most definitive evidence why: the nicotine in cigarettes.

Xiao-Chuan Liu, a professor of chemistry at the California State Polytechnic University, presented results from his study of blood samples from diabetic smokers at the American Chemical Society national meeting and exposition. He found that nicotine, when added to human blood samples, raised levels of hemoglobin A1c (HbA1c) by as much as 34%.

Hemoglobin A1c -  a combination of hemoglobin (which ferries oxygen) and glucose — is a standard indicator of blood sugar content in the body.

Doctors always knew smoking can make diabetes worse, but, Liu says, “now we know why. It’s the nicotine. This study also implies that if you are a smoker, and not diabetic, that your chances of developing diabetes is higher.”

The higher A1c levels rise in the blood, he says, the more likely it is that other protein complexes, which build up in various tissues of the body, from the eyes, heart and blood vessels, can form, leading to blockages in circulation and other complications.

But perhaps more importantly, the results also suggest that nicotine replacement products such as patches and nicotine-containing electronic cigarettes, aren’t a safe option for diabetes patients either. Because they still contain nicotine, these products are just as likely to boost A1c levels as cigarettes are. “In order to minimize your chances of developing diabetes or diabetic complications, you need to quit smoking,” says Liu. Even it means going cold turkey.

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By Alice Park