Published on 6 June 2018

Smokers 15-30% more likely to be diagnosed with type 2 diabetes than non-smokers – according to study in China.

Researchers in China have found that people who smoke have a significantly higher risk of developing type 2 diabetes.

According to a recently published report in The Lancet the habit of smoking is a contributing factor to developing the condition.

Since the 1980s the number of people diagnosed with type 2 diabetes in China has multiplied by 10 - with one in 10 adults now estimated to have the condition.

Although obesity is most commonly identified as a contributing factor for people being diagnosed with type 2 diabetes recent studies in China have found that is contributes to around 50% of the increase in new diagnoses of the condition in recent decades.

Studies into how other lifestyle factors, including smoking, may be a cause in new cases of type 2 diabetes have been investigated by researchers from the University of Oxford, UK, the Chinese Academy of Medical Sciences and Peking University

In recent decades, there has been a large increase in cigarette smoking in China, especially among men. It is estimated that around two thirds of Chinese men now smoke, consuming 40% of the world’s cigarettes in the process.

Researchers looked at the link between smoking and not smoking in a large, nationwide study of 500,000 adults who did not have type 2 diabetes from 10 areas (five urban and five rural) of China.

Over the course of a nine year study 13,500 participants were newly diagnosed with type 2 diabetes.

The researchers found that, compared with people who had never smoked, regular smokers had a 15-30% higher risk of developing type 2 diabetes, after taking account of the effects of age, social status, alcohol consumption, physical activity and weight.

The amount smoked and the earlier a person started smoking were also found to increase this risk.

Man smoking a cigarette.

Among men, the smoking-associated risk of developing type 2 diabetes was higher among people who were overweight.

Compared with people who never smoked, smoking 30 cigarettes or more per day was associated with a 30% higher risk of developing type 2 diabetes among men with a normal weight but with a 60% higher risk among men who were obese.

Smokers, on average, tended to be thinner than non-smokers, believed to be due to appetite suppression and an elevated resting metabolic rate associated with smoking. However, heavy smokers were more likely to have more fat than light or non-smokers, greatly increasing the risk of developing type 2 diabetes.

Study author, Professor Zhengming Chen, from the University of Oxford, UK, said: “The excess smoking-associated risk of diabetes among men in China is likely to increase substantially in future generations because the tobacco epidemic is maturing, but also because levels of overweight and obesity continue to rise among adults in China.”

Previous studies have suggested that giving up smoking may increase the risk of developing type 2 diabetes, at least in the short term. By carefully analysing information on the reasons why people stopped smoking, the study demonstrated that this excess risk of diabetes among recent quitters was only seen in those who had stopped smoking because of illness, and not those who chose to stop smoking for other reasons. Among individuals who had chosen to give up smoking and had stopped for more than 5 years, there was a small excess risk of diabetes, but this could be explained by moderate weight gain following smoking cessation.

Study co-author, Dr Fiona Bragg, from the University of Oxford, UK, said: “These findings add to existing evidence of the health benefits of giving up smoking, not only for prevention of cancer, respiratory and cardiovascular diseases, but now also for prevention of type 2 diabetes.”

Although smoking is much less common among women in China, the risks of developing type 2 diabetes linked to smoking appeared to be greater among women than men for a given amount smoked. Researchers believed this may be explained in part by their greater proportion of body fat compared with men.

Study author, Professor Liming Li, Peking University, China, said: “We can’t conclude from these findings that smoking causes type 2 diabetes, but, irrespective of this, smoking should be targeted as an important modifiable lifestyle factor in future disease prevention strategies, including for diabetes, in China and elsewhere.”

Read the report in The Lancet
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