Simple lifestyle and environmental changes could significantly help to cut the number of cancer deaths around the world each year, research suggests.
Obesity is a key risk factor for cancer
Experts linked more than a third of the seven million cancer deaths worldwide in 2001 to nine potentially modifiable risk factors.
These include poor diet, smoking, alcohol, obesity, lack of exercise and air pollution.
The Harvard University study is published in The Lancet.
The researchers calculated that of the seven million deaths from cancer in 2001, 2.43 million were linked to the nine risk factors.
MODIFIABLE RISK FACTORS
Low fruit and vegetable intake
Lack of exercise
Urban air pollution
Indoor smoke from household use of coal
The findings were based on a comprehensive review of scientific studies and other sources such as government reports.
The Harvard team and their collaborators also re-analysed some of the original data from the studies.
They concluded that in low and middle-income countries the most important risk factors were smoking, alcohol use, and low consumption of fruit and vegetables.
In high-income countries, smoking, alcohol use, and obesity played the leading role.
Deaths could be cut
Lead researcher Dr Majid Ezzati said that smoking was by far the most important risk factor for cancer - alone responsible for 21% of cancer deaths worldwide.
He said public health campaigns targeting smoking in the UK had led to a drop in deaths from lung cancer in the past few decades, and showed just how effective such campaigns could be.
He said: "Primary prevention through lifestyle and environmental interventions remains the main route for reducing the global cancer burden.
"If implemented, reduction of exposure to well-known behavioural and environmental risk factors would prevent a substantial proportion of deaths from cancer."
Dr Kat Arney, of the charity Cancer Research UK, said: "This report is an impressive demonstration that many cancers, and many deaths from the disease worldwide, are preventable.
"Cancer Research UK estimates that around half of all cancers in the UK could be prevented by changes to lifestyle."
The charity has launched a Reduce the Risk campaign, encouraging people to quit smoking, stay in shape, eat and drink healthily, avoid excessive sun exposure, be body aware and go for screening when invited.