Body weight and cancer: the evidence
This page contains information about the links between bodyweight and cancer. Click on the links below to read about specific topics.
On this page
- The Ten Top Tips are proven strategies to take in fewer calories and burn more energy through activity
- Obesity is a major preventable cause of cancer
- Obesity increases the risk of breast cancer in women after menopause
- Obesity increases the risk of bowel cancer
- Obesity increases the risk of womb cancer
- Obesity increases the risk of oesophageal cancer
- Obesity increases the risk of gastric cardia cancer
- Obesity increases the risk of pancreatic cancer
- Obesity increases the risk of kidney cancer
- Obesity increases the risk of gallbladder cancer
- Obesity increases risk of many other types of cancer
- Too much belly fat could increase the risk of cancer
- Obesity may increase cancer risk by changing hormone levels
- Keeping a healthy weight reduces cancer risk and losing weight may reduce cancer risk
- Parents can reduce their children’s cancer risk in adult life by encouraging them to eat healthily and keep active
Cancer Research UK and Weight Concern teamed up to develop a programme to help people keep a healthy weight. The tips are based on research and scientific evidence.
One study looked at the effect of giving the Ten Top Tips leaflet to people trying to lose weight. Eight weeks later, people who had used the leaflet had lost an average of 2 kg, compared to 0.4 kg in those who didn’t receive the leaflet. After eight months, people using the leaflet had lost an average of 3.8 kg, and also reported an improvement in quality of life.
A small study of people using the Ten Top Tips leaflet also found that initially, it was an effort to remember to use some of the tips, but that over time it got easier to remember to follow the tips, until they became automatic.
In general, it takes different people different amounts of time to develop habits like those suggested in the Ten Top Tips.
Evidence shows that making small, simple changes can develop into healthy habits that have a long-term impact on behaviour and health.
Major studies confirm that being overweight or obese increases the risk of various cancers. The World Health Organisation (WHO) says that overweight and obesity are the most important known avoidable causes of cancer after tobacco.
Researchers estimate that overweight and obesity are behind around 17,000 cases of cancer each year in the UK. This number may well increase in the future since the number of people who are overweight is increasing.
The latest statistics for England show that the proportion of adults with a healthy BMI decreased, and around a quarter of adults are obese, and the figures are similar in the other UK nations.
Scientists have estimated that anywhere between 7% and 15% of breast cancer cases in developed countries are caused by obesity. Over a hundred studies show that women who are overweight or obese and have been through the menopause have higher breast cancer risks.
Two large studies funded by Cancer Research UK - the EPIC study and the Million Women Study - have found that obese women have a 30% higher risk of postmenopausal breast cancer than women with a healthy weight.
Obesity does not increase the risk of breast cancer in women before their menopause. Putting on weight over time can also increase the risk of breast cancer. Studies have found that:
• putting on 2-10 kg (4.4 - 22 lb) after the age of 50 increases the risk of breast cancer by 30%.
• putting on 25 kg (55 lb) after the age of 18 increases the risk of breast cancer by 45%.
Obesity is one of the most important causes of bowel cancer. Some groups have estimated that being overweight or obese causes about 11-14% of bowel cancer cases.
Many large studies have found that bowel cancer is more common in overweight or obese people. Two of the largest studies so far, including the EPIC study, have found that obese men have about 50% higher risks of bowel cancer than those with a healthy weight.
When BMI is used to measure body fat, studies tend to find that only obese men have a higher risk of bowel cancer. But when researchers use waist circumferences or waist-to-hip ratios, both obese men and women have higher risks of bowel cancer. This suggests that, for women at least, fat around the stomach is more of a problem than fat elsewhere on the body.
A large body weight is one of the most important causes of womb cancer. A 2011 study estimated that more than a third of womb cancers in the UK are caused by being overweight or obese.
Studies have consistently found that obese people are two to three times more likely to develop womb cancer than people with a healthy bodyweight.
Being overweight or obese increases the risk of a type of oesophageal cancer (cancer of the foodpipe) called “oesophageal adenocarcinoma”.
Overweight people are over 80% more likely to develop this cancer than people of a healthy weight, and the risk in obese people is even more.
Experts have estimated that in the UK it causes about 1 in 5 cases of this type of cancer. In fact, the rates of oesophageal adenocarcinoma in the UK are among the highest in the world, especially in men. Some studies have suggested that, in Western countries, this type of cancer may be becoming more common because of rising levels of obesity.
The gastric cardia is the part of the stomach that is connected to the oesophagus. Cancer of this part of the stomach has become more common in developed countries, and scientists think that this is closely linked to obesity. This cancer can sometimes be referred to as cancer of the oesophagogastric junction or gastroesophageal junction.
As with oesophageal cancer, more than 1 in 5 cases of this cancer may be caused overweight or obesity, and the risk is higher for those who also smoke. The risk of gastric cardia cancer is nearly doubled in obese people compared to those of a healthy weight.
Higher BMI and fat around the belly are both linked to a 10-14% increased risk of pancreatic cancer in men and women. We don’t have clear evidence about exactly why this is, but it may be linked to some of the changes in hormone levels that are caused by obesity.
The risk increases with higher BMI, and it is estimated that around one out of ten pancreatic cancers may be caused by being overweight or obese. Those who are overweight when they are younger and gain more weight as they get older are at around 50% higher risk than those who keep a healthy weight from the age of 18.
Studies have estimated that having a high body weight accounts for nearly a quarter of kidney cancers. And many studies have consistently shown that higher BMI is linked to an increased risk of kidney cancer. The most recent study into the size of the risk showed that higher BMI increases the risk of kidney cancer by 31%.
Obesity is known to cause formation of gallstones, which can increase the risk of cancer of the gallbladder. And the hormonal changes that result from having more body fat can also increase the risk of gallbladder cancer.
It is estimated that nearly a fifth of gallbladder cancers result from people being overweight or obese. Compared to men, more than double the number of cases in women seem to be linked to excess body weight.
There is some evidence that being overweight or obese could increase the risk of many other types of cancer, including:
- brain cancer
- liver cancer
- multiple myeloma
- non-Hodgkin lymphoma
- ovarian cancer, before the menopause
- aggressive prostate cancer
- thyroid cancer
But the evidence for a link with these other cancer types is not strong enough to know for sure if there is a link.
The way that fat is distributed around the body can also affect the risk of cancer. ‘Apple-shaped’ people who put on weight around their stomach may have higher risks than ‘pear-shaped’ people who put on weight around their hips.
Scientists measure belly fat using either waist circumference (the length of tape that goes around your waist) or waist-to-hip ratio (how wide your waist is compared to your hips). Studies have found that people with larger waists or waist-to-hip ratios have higher risks of breast cancer, bowel cancer in men and women, kidney cancer, and pancreatic cancer.
Obesity most likely increases the risk of cancer by raising levels of hormones such as oestrogen and insulin.
In early life, oestrogen is mainly produced by a woman’s ovaries, but this stops after menopause. Instead, fat in the body becomes the main source of oestrogen and obese women have up to twice as much oestrogen as women with a healthy weight. They also have lower levels of SHBG, or ‘sex hormone binding globulin’, which mops up oestrogen in the body. This is almost certainly why obesity increases the risk of breast and womb cancers.
Obesity also increases levels of insulin in the body. It’s not clear how this could lead to cancer, although high insulin levels are a common feature of many cancers. High insulin levels could explain why being obese increases the risk of liver, womb, bowel, kidney and pancreatic cancer.
Obesity could also cause cancer through other means, including:
- increasing the risk of oesophageal and gastric cardia cancers by causing ‘gastric acid reflux’, a condition where the stomach’s acids are briefly pushed back into the throat. This damages the lining of the oesophagus and the area where it connects to the stomach.
- increasing the risk of gallstones, which in turn increase the risk of gallbladder cancer.
- being associated with physical inactivity or unhealthy diets.
Studies have shown that overweight and obese people are more likely to develop cancer than people with a healthy body weight . It therefore makes sense that losing weight can help to reduce the risk of cancer. It is difficult to design studies to confirm this, but some large studies have found that losing weight can help reduce the risk.
One study found that women who lost 20 pounds or more had 11% lower risks of cancer overall compared to women who had never lost that much weight. Another study found that women who lost 10kg since menopause, and kept the weight off, more than halved their risk of breast cancer. Other studies have found similar results for breast and other types of cancer.
A review of many studies found that, overall, that the risk of cancer is lower for people that intentionally lose weight, compared to those who don’t.
When people try to lose weight through short-term fixes, in most cases, they end up putting the weight back on. It’s unclear how this ‘weight cycling’ affects the risk of cancer.
One study found that women whose weight had gone up and down by over 10 pounds, more than ten times, had higher risks of kidney cancer than those whose weight was stable. Another study found that in women that had ever had a BMI of 30 or higher, those that lost and gained 9 kg or more at least once were nearly three times more likely to develop womb cancer. And there are indications that it may also increase the risk of non-Hodgkin’s lymphoma.
While weight cycling is a new area of research and only a few types of cancer have been studied, it does suggest that the best way to reduce the risk of cancer is to maintain a healthy bodyweight over time.
Eating habits established in childhood often endure after many years. In 1993, a group of scientists showed that at least half of obese children were still obese as adults. And a more recent study in Finland recorded children’s weight or BMI at 5 months, 1 year, ages 2-5, and finally at age 3.
They found that children with the highest BMI from the age of 3 were over three times more likely to be obese. Another study of Scottish and English children found that people who are obese as children have higher risks of some cancers later on in life.
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