Introduction We estimate the percentage of cancer in the UK in 2010 resulting from exposure to 14 major lifestyle, dietary, and environmental risk factors.

Methods RRs and prevalence of exposure to tobacco, alcohol, four dietary components (fruit and veg, meat, fibre, salt), overweight, physical exercise, occupation, infections, radiation, hormone use, and reproductive factors were used to estimate the number of cancers occurring in 2010 attributable to sub-optimal exposure levels in the past.

Results The 14 exposures were responsible for 42% of cancer in UK in 2010 (males 44%, females 40%). Tobacco smoking is the most important, responsible for about 60 000 new cancers (18.5% of all cancer - 22% in men, 15% in women); <2% being the result of exposure to ETS. The four dietary components account for 9.4% of cancer (10.7% in men, 7.1% in women). In men, alcohol (5.1%) and occupational exposures (4.7%) are next in importance; in women, it is overweight and obesity (almost 7% of cancers).

Conclusions Such estimates provide a quantitative appraisal of the impact of different exposures. They are not synonymous with the fraction of cancers that might reasonably be prevented by their modification. This requires scenario modelling, with assumptions on a realistically achievable population distribution of risk factors, and the timescale of change. Thus, although 50% of colorectal cancer can be attributed to lifestyle (diet, alcohol, inactivity and overweight), only about half of this number is preventable in a reasonable (∼20 year) timescale.