New research suggests that quitting smoking may raise the risk of developing type 2 diabetes in the short term, and as ex-smokers log more years without touching cigarettes, that risk gradually comes down to that of a never-smoker; the researchers suspect weight gain is the main reason and warn quitters to watch their weight.

These are the findings of a study by researchers from the Johns Hopkins University School of Medicine in Baltimore, Maryland, the University of North Carolina at Chapel Hill, both in the US, and the Federal University of Rio Grande do Sul in Porto Alegre, Brazil.

Cigarette smoking is already a well-established risk factor for type 2 diabetes, but when smokers quit, they typically put on extra pounds.

Lead author, Dr Hsin-Chieh “Jessica” an assistant professor of general internal medicine and epidemiology at Johns Hopkins, told the media that they suspect weight gain by quitters is the main reason why the diabetes risk goes up in the short term.

She and her colleagues stress that these findings should not be used as an excuse to keep smoking, which is also a risk factor for lung disease, heart disease, strokes, and several types of cancer.

“The message is: Don’t even start to smoke,” she said.

“If you smoke, give it up. That’s the right thing to do. But people have to also watch their weight,” she added.

For the study, the researchers enrolled 10,892 adults of middle age who had not been diagnosed with diabetes from 1987 to 1989. They followed them for 17 years and regularly collected data on diabetes status, glucose levels, weight, and other measures.

The measures were taken in different ways: smoking status was assessed by interview at the start of the study, and during follow up. Incident diabetes was assessed from fasting glucose tests up to 1998, self-report of diagnosis by a doctor, or use of diabetes medication up to 2004.

The results showed that:

  • Over 9 years of follow up, 1,254 of the subjects developed type 2 diabetes.

  • Compared to adults who never smoked, the heaviest smokers (the top third measured by pack-years) had an estimated 42 per cent higher risk of developing diabetes (adjusted hazard ratio 1.42, with 95 per cent confidence interval, CI, ranging from 1.20 to 1.67).

  • In the first 3 years of follow up, 380 of the subjects quit smoking.

  • On average, over those first three years, quitters gained about 8.4 pounds (3.8 kilos) and their waist circumferences grew by approximately 1.25 inches (3.2 cm).

  • After adjusting for several confounders, including age, race, sex, education, adiposity, physical activity, blood fat levels (lipids), blood pressure, and data collection source, compared with never smokers, the estimated relative risk of developing diabetes varied among former smokers (HR 1.22, CI 0.99-1.50), new quitters (1.73, 1.19-2.53) and continuing smokers (1.31, 1.04-1.65).

  • These risks changed substantially when the researchers took into account weight change and leukocyte count.

  • In an analysis of what the long term risk might be after quitting, the highest risk occured in the first 3 years (HR 1.91, CI 1.19 – 3.05), then gradually went down to zero at 12 years.

The researchers concluded that:

“Cigarette smoking predicts incident type 2 diabetes, but smoking cessation leads to higher short-term risk.”

“For smokers at risk for diabetes, smoking cessation should be coupled with strategies for diabetes prevention and early detection,” they added.

Type 2, or adult onset, diabetes is a common disease that screws up the way our bodies use sugar and control insulin, a pancreas-produced chemical that normally lowers blood sugar after eating.

In people with type 2 diabetes the pancreas makes plenty of insulin but the body can’t use it properly, leaving too much sugar in the blood, which in the long run can result in blindness, heart disease, kidney failure and nerve damage.

People who are overweight, and who have a family history of the disease are at higher risk of developing type 2 diabetes, and smokers are also at higher risk, but exactly how smoking leads to diabetes is not clear.

In this study, the researchers found that the heaviest smokers, and the quitters who put on the most weight, had the highest risk of developing diabetes.

They suggest doctors and healthcare practitioners helping smokers to quit should bear these findings in mind, especially where the heaviest smokers are concerned. They urge them to consider offering more lifestyle counselling, aggressive weight management, and nicotine replacement therapy to support quitters, and to do more blood glucose screening to ensure early detection of any signs of developing diabetes.

The National Heart, Lung and Blood Institute and the National Institute of Diabetes, Digestive and Kidney Disorders, both of the National Institutes of Health, funded the study.

“Smoking, Smoking Cessation, and Risk for Type 2 Diabetes Mellitus: A Cohort Study.”
Hsin-Chieh Yeh, Bruce B Duncan, Maria Inês Schmidt, Nae-Yuh Wang, and Frederick L Brancati.
Ann Intern Med January 5, 2010 152:10- 17.

Source: Johns Hopkins Medicine.

Written by: Catharine Paddock, PhD