Obesity is set to overtake smoking as the biggest preventable cause of cancer among UK women in 25 years’ time, according to a Cancer Research UK report.

These new projections calculate that in just 17 years (2035) 10% of cancers in women (around 25,000 cases) could be caused by smoking and 9% (around 23,000 cases) by excess weight.

But by 2043, if trends continue as projected, excess weight could cause even more cases of cancer than smoking in women.

The figures for men are different because the gap between obesity and tobacco as causes of cancer is expected to close much later than in women. And since more men smoke they are more likely to have tobacco-related cancers.**

While more males than females are overweight or obese, obesity has a greater effect on women, as some of the most common obesity-related cancers predominantly affect them – such as breast and womb cancers.

Being overweight or obese as an adult increases the risk of 13 different types of cancer including breast, bowel and kidney cancer,*** but only around one in seven people in the UK are aware of the link.****

Today, Cancer Research UK is launching a UK-wide campaign to increase awareness that obesity is a cause of cancer.

Professor Linda Bauld, Cancer Research UK’s prevention expert, said: “Obesity is a huge public health threat right now, and it will only get worse if nothing is done. The UK Government must build on the lessons of smoking prevention to reduce the number of weight-related cancers by making it easier to keep a healthy weight and protect children, as those who are overweight are five times more likely to be so as an adult.

Professor Linda Bauld, Cancer Research UK’s prevention expert

Professor Bauld continues “That’s why we are raising awareness of the link between cancer and obesity and calling for measures to protect children like a ban on junk food adverts before 9pm and for restrictions on price promotions of ‘less healthy’ products.

“The decline in smoking is a cause for celebration. It shows how decades of effort to raise awareness about the health risks plus strong political action including taxation, removing tobacco marketing and a ban on smoking in indoor public places, have paid off. But, just as there is still more to do to support people to quit smoking, we also need to act now to halt the tide of weight-related cancers and ensure this projection never becomes a reality.”

Cancer UK references

*Calculated by the Cancer Intelligence Team at Cancer Research UK, August 2018. Report available upon request.

The report uses the established epidemiological method of Population Attributable Fractions (PAFs) to combine projections of cancer incidence, smoking prevalence and overweight and obesity prevalence, in order to calculate the number and proportion of UK cancer cases attributable to each factor in 2025-2035, based on risk factor prevalence 10 years prior (e.g. risk factor prevalence in 2025 impacts cancer incidence in 2035).

Projections of cancer incidence beyond 2035 are less precise but if the smoking-obesity gap continues to narrow after 2035 at the rate calculated for 2025-2035, it is estimated that being overweight or obese could cause more cancer cases than smoking in UK females by 2043.

For UK males this crossover is likely to occur much later, as by 2035, smoking is still estimated to cause nearly twice as many cancers in males than excess weight. But it is not possible to estimate a timeframe for this as it is too far in the future to project reliably.

While a ‘crossover’ between smoking and being overweight or obese appears almost inevitable if trends continue, the precise point at which this will occur is difficult to predict, and the results presented here, using the most accurate tools we have, are indicative rather than definitive.

**For men, 13% (more than 34,000 cases) of cancers could be caused by smoking by 2035 with 7% (around 18,000 cases) caused by excess weight.

*** ONS Cancer Awareness Measure 2017

**** Brown et al. The fraction of cancer attributable to known risk factors in England, Wales, Scotland, Northern Ireland, and the UK overall in 2015. British Journal of Cancer. DOI: 10.1038/s41416-018-0029-6. http://www.nature.com/articles/s41416-018-0029-6.