Obesity causes cancer

Cancer cells - fotoloia

The links between obesity and heart disease and diabetes are well documented. What remains less known is the emerging link between too much bodyweight and cancer.

Having excess fat in the body is now linked with 13 types of cancer, including some of the most common kinds such as breast cancer and bowel cancer.

The link with oesophageal, pancreatic, kidney and womb cancers is also now well evidenced, while links with cancer of the brain, thyroid, liver, upper stomach, gallbladder, ovaries and blood are emerging.

Being overweight or obese is the second most important preventable cause of cancer after tobacco, according to the World Health Organisation.

And with two thirds of Scots now overweight or obese, it is a significant issue. Studies have shown that if trends continue, almost three quarters of the UK population will be overweight or obese by 2035. This would undoubtedly increase the burden of cancer on society and NHS resources, not to mention the impact on heart disease, diabetes and mental health.

It is remarkable then, that it appears the link between obesity and cancer is relatively unknown amongst the public.

A UK-wide survey by Cancer Research UK (CRUK) in 2016 found three-quarters of people were unaware of the link. Men and people in lower socioeconomic areas were even less likely to know about the increased risk of cancer.

Speaking at the launch of the report, Alison Cox, director of prevention at CRUK, said: “Cancer isn’t at the forefront of people’s minds when talking about obesity and that’s really concerning. Few understand that excess weight increases the risk of several cancers, including some of the most common such as breast cancer.  

“It’s the Government’s responsibility to inform the public of the link and also to take action to tackle the obesity epidemic, starting with the health of the nation’s children.”

CRUK has been active in campaigning for the inclusion of greater regulation of the marketing and price promotions of junk food in the Scottish Government’s long-awaited obesity and diet strategy.

And although campaigners are still waiting to see what the strategy will look like amid rumours of disagreements between government departments on elements of the approach, there was a hint in First Minister Nicola Sturgeon’s programme for government.

“We will take forward a new strategy to tackle obesity, including measures to restrict the marketing of foods that are high in fat, sugar or salt,” Sturgeon told MSPs.

It was little more than a passing reference, but later a government spokesperson insisted this could include multi-buy promotions.

CRUK’s cancer prevention expert in Scotland, Linda Bauld, who is based at the University of Stirling, gave the commitment a cautious welcome.

“The Scottish Government’s commitment to limit junk food marketing is a step in the right direction, but to progress, regulations are needed to restrict multi-buy offers on unhealthy food and drink,” she said.

“Obesity is linked to 13 different types of cancer. As part of its forthcoming obesity strategy, the Scottish Government must grasp the opportunity to help families make it easier to keep a healthy weight.

“Measures to help us enjoy a better diet and fill our shopping baskets with healthy food will make it easier for us all to stack the odds of not getting cancer in our favour.”

To raise awareness among the public, CRUK is running an ‘obesity and cancer awareness week’ this week alongside Obesity Action Scotland. This will include a billboard campaign and a fringe at SNP conference.

But what exactly is the link between obesity and cancer?

Bauld tells Holyrood that “abnormal cell makeup” can be a product of excess fat cells in the body.

The fat can be active in producing hormones and proteins into the bloodstream. 

Immune cells can be affected, causing inflammation. The levels of hormones like oestrogen can be altered, increasing the risk of breast and womb cancers. Obese women have up to twice as much oestrogen as women with a healthy weight.

Obesity also increases levels of insulin in the body, but it’s not yet clear how this can lead to cancer.

And studies suggest fat around the stomach can be more of a problem than elsewhere in the body, especially when it comes to bowel cancer. 

“The science is moving on all the time,” says Bauld. “CRUK is funding a lot of work in this area and we can be very confident that these links exist. 

While people might be able to picture why their diet might contribute to the clogging of their arteries, might its impact on their cells be harder to grasp?

“I remember talking to oncologists who treat women for things like womb cancer, which has a very clear link to obesity, and the ladies in the clinic – they were heavy ladies – said ‘nobody ever told me that my weight might cause this cancer, or might contribute to this cancer’, and I think it is difficult for doctors to explain what the mechanisms are.

Also, because the understanding of these links is more recent, it not just the public which has a lack of awareness but also some in the medical profession, Bauld says.

“When I talk to oncologists and others in Scotland they say that they’ve only more recently become aware.”

Furthermore, family doctors can find it difficult to talk to their patients about their weight. CRUK has designed a training module with the Royal College of General Practitioners which advises GPs on how to talk to their patients about their weight. 

“Not just GPs, but other doctors, if they are going to talk to patients about their weight, they need to be able to offer something,” adds Bauld.

“We know from the research generally, from smoking alcohol and weight, that telling patients to do something makes a difference, but what makes even more of a difference is to be able to refer them somewhere.”

Bauld points to a study at Oxford University which saw GPs referring patients to commercial weight loss programmes such as Slimming World and Weight Watchers, which improved outcomes and also led to an increased awareness among GPs.

“An issue for the Scottish Government, and I know they’re thinking about this in the diet and obesity strategy, is better provision across Scotland of weight management and weight loss services, because it’s very patchy.”

The surge in awareness of the risks of smoking led to a situation where only three per cent of doctors smoke, she points out.

Obesity’s link with cancer goes further than the direct links. It is also associated with physical inactivity and unhealthy diets, both of which are also independent risk factors for cancer.
Not having enough fibre, for example, can contribute to bowel cancer in particular.

“If you think about the middle of our body, things moving properly through our system, fibre is really important,” Bauld says.

“The other thing of course is fruit and vegetables. We know that the vitamins and minerals we get from a balanced diet support healthy cells, which again reduce the risks of cancer.”

Furthermore, physical inactivity is an independent risk factor for cancer, particularly for breast, bowel and womb cancer. Although physical activity has “a role to play” in tackling obesity, diet is the “key thing” says Bauld. 

“Being too sedentary, not taking enough physical activity, is independently linked to cancer,” she says. “The independent risk factor is more about the benefits physical activity has for the body. If you are very sedentary that affects how our body functions. If you think about our digestive system, physical activity really helps with that and it helps maintain a healthy circulation.”

Ongoing trials are also showing good fitness levels among those who have had cancer may contribute to preventing it coming back. 

As with everything, lifestyle is directly affected by mental health. Bauld describes the “pathway”, which includes primary preventable risk factors such as diet and smoking, and environmental factors such as radiation and pollution.

“There are things that interact with those risk factors. Poverty, poor housing and poor mental health clearly all contribute to people engaging in lifestyle factors which are going to increase their risk of cancer. There’s no doubt about that.”

CRUK, she says, is interested in working with others to “promote health in its broadest sense. Mental health has to be part of that”.

But in terms of the forthcoming obesity strategy, Bauld says people cannot be expected to lower their risk of cancer without support.

“The key thing for members of the public and health professionals is really to support people to not put on weight in the first place. That’s the ideal thing. But if they are overweight, we need to support them to lose that weight and reduce their cancer risk.” 

Feature in association with Cancer Research UK