Smokers and those exposed to secondhand (passive) smoke have a much higher risk of developing type 2 diabetes, a new study has found.

According to the findings, more than 27 million cases of type 2 diabetes worldwide may be due to smoking.

"Cigarette smoking should be considered as a key modifiable risk factor for diabetes. Public health efforts to reduce smoking will have a substantial impact on the global burden of type 2 diabetes," commented the study's co-author, Prof Frank Hu, of the Harvard School of Public Health in the US.

While smoking is already known to increase the risk of a number of diseases, such as cancer and heart disease, a link between smoking and type 2 diabetes has, until now, been more difficult to establish.

Working with researchers from China and Singapore, the US team carried out a detailed analysis of 88 studies on this topic. These studies included almost six million people.

The analysis revealed that current smokers had a 37% increased risk of developing type 2 diabetes compared to non-smokers, while passive smokers had a 22% increased risk. Former smokers had a 14% increased risk.

Among smokers, the risk of developing type 2 diabetes increased the more they smoked. Compared with people who had never smoked, light smokers had a 21% increased risk, moderate smokers had a 34% increased risk and heavy smokers had a 57% increased risk.

The researchers estimated that over 11% of cases of type 2 diabetes in men, and 2.4% of cases in women, are due to active smoking - that is 27.8 million people worldwide.

Details of these findings are published in the journal, The Lancet Diabetes & Endocrinology.