Unhealthy lives now the biggest threat to health

The rise in cancer linked to poor diet and a lack of exercise poses as much of a problem in the 21st Century as providing access to clean water did in the 19th Century when outbreaks of cholera could wipe out entire populations, he said.

And Professor Martin Wiseman, medical and scientific adviser for the World Cancer Research Fund (WCRF), warned that while the increase in many cancers is linked to the fact people are living longer, around 80,000 cases could be prevented every year in the UK if people ate better, kept to a healthy weight and exercised.

Around one in three of the most common cancers in high-income countries and about one in four in medium and low income countries could be stopped if people led healthier lives, estimates suggest.

According to the United Nations, the number of deaths from cancer worldwide is set to double by 2030.

And global cases of cancer have risen dramatically in the past 30 years, from 6.3 million cases in 1980 to 8.1 million in 1990 and 11.3 million in 2007.

But Prof Wiseman said this doubling was not inevitable and more should be done to prevent lifestyle cancers.

He was speaking ahead of the WCRF's international scientific conference in London, which will hear from speakers from the World Health Organisation and the International Agency for Research on Cancer.

"It is clear that the rising number of lifestyle-related cancers is one of the biggest challenges facing the world today," he said. "It is important we do not underestimate it.

"The challenge we face in preventing cancer is of the same scale as people faced in making drinking water freely available in the 19th Century in urban areas.

"We have seen over the last century that, as countries have become more industrialised, people in those countries have become more overweight, less active and eaten more processed foods.

"But this does not have to happen. By making changes that make it easier for people to make healthy choices, and by giving people the information they need to make their own informed choices, we can avoid the typical path of developing the unhealthy behaviours that have promoted chronic diseases in the 20th and 21st Centuries.

"It is important to remember it is largely because of our successes in preventing the spread of communicable disease that people are now living long enough for cancer to be affecting a significant proportion of the world's population. This is because cancer is mostly a disease of old age.

"But unless we can stop the rising number of lifestyle-related cancers, this will mean that millions of people will die unnecessarily young."

It is estimated that a quarter of all cancer deaths are caused by unhealthy living and obesity.

Cancers affected by lifestyle include those of the bowel, stomach, mouth, foodpipe and breast.