About a third of all common cancers in the United States, China and Britain could be prevented each year if people ate healthier food, drank less alcohol and exercised more, health experts said on Friday.

Estimates from the American Institute for Cancer Research (AICR) and the World Cancer Research Fund (WCRF) suggest that making simple lifestyle changes could prevent some 40 percent of breast cancers alone in Britain and the United States, as well as tens of thousands of colon, stomach and prostate cancers.

The WCRF findings are backed by World Health Organisation (WHO) recommendations, which say regular exercise can prevent many diseases such as cancers, heart diseases and diabetes.

Cancer is a leading cause of death around the world and its incidence is rising. Each year around 12.7 million people discover they have cancer and 7.6 million people die from some form of the disease. There are about 200 known types of cancer.

According to the International Agency for Research on Cancer (IARC), cancer will kill more than 13.2 million people a year by 2030, almost double the number it killed in 2008 -- and the vast majority of deaths will be in poorer countries.

In a separate statement, the Geneva-based WHO said low levels of physical activity are the main cause of an estimated 21 to 25 percent of breast and colon cancers, 27 percent of diabetes cases and 30 percent of heart disease cases worldwide.

Rachel Thompson, the WCRF's deputy head of science, said that while the message was simple -- that not smoking, eating good food and being a healthy weight can help ward off many cancers -- it was still a difficult one to get across.

The WHO says adults should do at least 150 minutes of moderate exercise a week. This could be done by walking for 30 minutes five times per week or by cycling to work every daTobacco kills millions of smokers every year, and tobacco-related lung cancers also kill hundreds of thousands of people who don't smoke but have been exposed to it second-hand.