Although smoking increases the risk of diabetes and quitting has numerous health benefits, diabetics who quit may have temporary difficulty controlling their symptoms, a British study finds.
Researchers reviewed medical records for 10,692 adult smokers with diabetes in the UK and found that smoking cessation led to an uptick in blood sugar levels that lasted three years and was not caused by weight gain.
"We know that smoking increases the risk of developing diabetes so when people stop smoking we would expect things to immediately improve; however, we found that things get a little worse in terms of glycemic control before they get better," lead author Dr. Deborah Lycett, of the faculty of health and life sciences at Coventry University in the UK, said by email.
Worldwide, nearly one in 10 adults had diabetes in 2014, and the disease will be the seventh leading cause of death by 2030, according to the World Health Organisation.
Most of these people have type 2 diabetes, which is associated with obesity and aging and happens when the body can't properly use or make enough of the hormone insulin to convert blood sugar into energy. Left untreated, diabetes can lead to nerve damage, amputations, blindness, heart disease and strokes.
Lycett and colleagues examined the impact of smoking cessation on diabetes symptoms by testing hemoglobin A1c, a protein in red blood cells that gets coated with sugar over time, making it a gauge of average blood sugar levels for the past two or three months. Diabetics have A1c levels of at least 6.5 per cent.
The study included more men than women, and most participants were white. At the start of the observation period in 2005, participants were 62 years old on average and had been living with diabetes for about six years. Many were taking at least one medication to lower blood sugar.
The group included 3131 people who quit smoking and remained abstinent for at least a year. Even after adjusting for factors such as age, gender and weight, there was a significant 0.21 per cent increase in A1c during the first year of cessation.
In the long term, blood sugar levels gradually decreased. By three years, the diabetics who quit smoking had blood sugar levels similar to the people who kept smoking.
While the researchers did account for cessation-related weight gain, it's still possible that the initial surge in blood sugar levels might be related to added pounds or dietary changes, the researchers wrote in the Lancet Diabetes and Endocrinology.
Establishing that cessation causes a short-term lapse in blood sugar control is unlikely to change clinical practice or recommendations to smokers, writes Amy Taylor, a tobacco researcher at the University of Bristol, in an editorial.
Even if smoking cessation doesn't directly cause blood sugar levels to increase, taking away cigarettes can lead to food cravings that influence blood sugar, Patricia Folan, director of the Center for Tobacco Control at North Shore University Hospital on Long Island, said by email.
"While smoking, individuals are basically administering an appetite suppressant (nicotine) every time they smoke," Folan, who wasn't involved in the study, said by email. "In heavy smokers, this can be 20 to 40 times a day."
To minimise the risk of blood sugar levels rising, smokers with diabetes should focus on developing healthy diet and exercise habits before they quit and then consider medications to control nicotine urges as well as blood sugar once they stop smoking, Folan said.
"The benefits of quitting smoking dramatically outweigh any potential extra, short term risk of having higher blood sugars," Dr. James Stein, a cardiovascular researcher at the University of Wisconsin School of Medicine and Public Health in Madison who wasn't involved in the study, said by email. "Smokers who quit should be careful to avoid risk factors for worsening glucose control - weight gain, diets high in sweets and carbs - and should exercise."