Obesity raises cancer risk by twice as much as previously thought, researchers find

The risk of obesity giving people cancer may be ‘considerably underestimated’, a study has warned.

Being fat may actually be more than twice as dangerous as previously thought when it comes to certain forms of the disease.

And excess weight is second only to smoking when it comes to avoidable cancer-causing lifestyles.

Bowel, kidney, pancreatic, ovarian, endometrial and oesophageal cancer are all now thought to be more affected by obesity than earlier estimates.

Experts said the study showed being severely overweight has ‘devastating effects’ and the British National Health Service (NHS) warned many people still don’t understand its risks.

Chief executive of the NHS, Simon Stevens, said: “While cancer survival is at a record high, many people don’t yet realise that obesity causes cancer. And now there is evidence that it’s a graver danger than first thought.

“If we continue to pile on the pounds, we’re heading for thousands more avoidable cancer deaths every year. The NHS… is playing its part but we cannot reverse the costly obesity epidemic alone, and families, food businesses and government all need step up and take action.”

The research, led by the France-based International Agency for Research on Cancer (IARC) looked at how genetic measures of body weight affected cancer risk.

It focused on seven forms of the disease – the six named above and breast cancer – which are thought to cause 80 per cent of obesity-related cancers in the United Kingdom (UK).

For many of them, the risk increase was around double what it had previously been thought to be, and for two it was multiplied by more than four times.

Previous estimates had been based on measures of someone’s height-to-weight ratio – their Body Mass Index (BMI) – while the new predictions were based on genetic markers of obesity.

These sections of Deoxy ribonucleic Acid (DNA)/genetic material, the scientists said, gave a more accurate picture of obesity over someone’s lifetime rather than at a single point in time.

And they showed the risk for kidney cancer, for example, rose from a 30 per cent increase to a 59 per cent increase.

It is important to note the figures are for relative risk, so an increase on the risk a healthy weight person has, and do not suggest that 59 per cent of obese people get kidney cancer.

The risk rose from 50 per cent to 106 per cent for endometrial cancer, from six per cent to 13 per cent for ovarian cancer and from 48 per cent to 110 per cent for cancer of the oesophagus.

For pancreatic cancer the obesity risk increase changed from 10 per cent to 47 per cent, and for bowel cancer it rocketed from five per cent to 44 per cent.

“Our analysis of genetic data for six of eight obesity-linked cancers indicated that the cancer burden associated with BMI may be considerably underestimated,’ the researchers, led by Dr. Daniela Mariosa, wrote.

They added: “These estimates would also make excessive body fatness the second most important cause of cancer in high-income countries, after tobacco.”

Obesity is known to make people more likely to get 13 types of cancer. These include breast, bowel, womb, oesophageal, pancreatic, kidney, liver, stomach, gallbladder, ovarian, thyroid and brain cancers, as well as myeloma.

According to Cancer Research UK (CRUK), fat cells send out signals which encourage other cells in the body to divide more often, which may lead to tumours forming.

Fat acts like a giant gland and increases levels of hormones such as oestrogen and insulin, which promote extra growth, CRUK said, as well as causing internal swelling.

How can obesity cause cancer? Obese people will not definitely develop cancer but they are at a higher risk than people who are a healthy weight. This is because fat cells are active in the body, releasing hormones and electrical signals which encourage cells to divide and grow.

Cancer is caused by an error in cell division which results in them multiplying uncontrollably and building up into tumours.

The more active cells a person has in their body, the higher the chance of one of them going rogue and triggering this chain reaction.

Obesity is also often associated with an unhealthy lifestyle – eating junk food and not getting enough fruit, vegetables or exercise – factors which are separate but linked and also known to increase the risk of cancer.