Bad lifestyle choices such as smoking, poor diet, high alcohol intake and excess weight are responsible for ‘around 40% of all cancers', according to new research.
These four factors alone account for a third of cancers diagnosed in the UK each year with another ten taking to total significantly higher.
The results mean that every year around 134,000 diagnosed cancers (45% in men and 40% in women) could be prevented.
Cancer Research UK's study found smoking was by far the most important lifestyle factor causing 23% of cancers in men and 15.6% in women, meaning almost one in five overall.
After tobacco, lack of fruit and vegetables in a person's diet was the second highest risk factor (6.1% in men, 6.9% in women).
These were followed by occupational risks (such as exposure to asbestos - 4.9% and 3.7%), alcohol (4.6% and 3.6%), overweight and obesity (4.1% and 3.4%) and excessive sun exposure and use of sunbeds (3.5% and 3.3%).
The review of cancer and lifestyle in the UK is the most comprehensive undertaken to date and is published in a supplement to the British Journal of Cancer.
Professor Max Parkin, study author and an epidemiologist for Cancer Research UK at Queen Mary, University of London, said: "Many people believe cancer is down to fate or ‘in the genes' and that it is the luck of the draw whether they get it.
"Looking at all the evidence, it's clear that around 40% of all cancers are caused by things we mostly have the power to change.
"We didn't expect to find that eating fruit and vegetables would prove to be so important in protecting men against cancer, and among women we didn't expect being overweight to have a greater effect than alcohol," he added.
Dr Harpal Kumar, chief executive of Cancer Research UK, noted: "Leading a healthy life doesn't guarantee that a person won't get cancer but this study shows that healthy habits can significantly stack the odds in our favour."
