Diabetes and obesity together are responsible for as many as 800,000 cancers worldwide every year, a new study has found.

Estimates suggest that 422 million adults worldwide have diabetes and 2.01 billion people are overweight or obese. This study marks the first time that researchers have quantified the number of cancers that are likely to be caused by diabetes and a high body mass index (BMI) together.

Using data from 2012, they found that almost 6% of all new cases of cancer that were diagnosed that year were caused by the combined effects of diabetes and excess weight. For the 12 types of cancer studied, this amounted to almost 800,000 cases.

Taken as individual risk factors, excess weight was responsible for twice as many cancers as diabetes - almost 545,000 cases versus just over 280,000 cases.

The researchers noted that cancers caused by diabetes and excess weight were almost twice as common in women (496,700) compared to men (295,900).

The team from Imperial College London said that if diabetes and obesity rates continue to rise, the share of cancers attributable to these two conditions together will jump by over 30% in women and by 20% in men by 2035.

The study involved data on 12 types of cancer from 175 countries. Among men, liver cancer was the most common type of cancer caused by diabetes and excess weight together. It accounted for 126,700 cases.

In women, breast cancer was the most common type of cancer caused by the two conditions together, accounting for 147,400 cases.

The most cancer cases caused by diabetes and excess weight were seen in high-income Western countries, with breast cancer the leading type of cancer diagnosed, accounting for almost 24% of all cancers.

"While obesity has been associated with cancer for some time, the link between diabetes and cancer has only been established quite recently. Our study shows that diabetes, either on its own or combined with being overweight, is responsible for hundreds of thousands of cancer cases each year across the world," commented the study's lead author, Dr Jonathan Pearson-Stuttard, of Imperial College London.

The researchers said that doctors need to be aware of the increased risk of cancer among their patients who are overweight, have diabetes, or both.

They also called for more effective food policies to tackle this issue.

"Both clinical and public health efforts should focus on identifying effective preventive, control and screening measures to structurally alter our environment, such as increasing the availability and affordability of healthy foods, and reducing the consumption of unhealthy foods," Dr Pearson-Stuttard added.

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