Being overweight and obese puts people at greater risk of developing the most common cancers, according to research in the Lancet medical journal.
Scientists calculated individuals carrying extra weight could contribute to a high number of cancer cases.
They warn if obesity levels continue to rise there may be an increase in cancer cases diagnosed annually. The study of five million people is the largest to date to confirm the link.
“This variation tells us BMI must affect cancer risk through a number of different processes, depending on cancer type.”
Dr Krishnan Bhaskaran, lead researcher stated.
Doctors often warn being overweight can increase the risk of developing cancer, but this study highlights those forms of the disease where the risk is greatest. Led by scientists from the London School of Hygiene and Tropical Medicine researchers gathered data on five million people living in the UK, monitoring changes to their health over a period of seven years.
They found each 13-16kg (2-2.5 stone) of extra weight an average adult gained was linked firmly and linearly to a greater risk of six cancers. How big this risk was varied depending on tumour type. Where cancer of the uterus had the highest increased risk and leukaemia had the lowest.
People who had a high body mass index (calculated using weight and height) were also more likely to develop cancer of the liver, colon, ovaries, and post-menopausal breast cancer.
But the effects for these cancers were less clear-cut and were influenced by individual factors such as the menopause.
Researchers say though obesity was associated with the development of the most common cancers – which represent 90% of the cancers diagnosed in the UK alone, some showed no link at all. And there is some evidence to suggest a higher BMI is associated with a lower chance of getting prostate cancer.
“There was a lot of variation in the effect of BMI on different cancers.”
Dr Krishnan Bhaskaran said. For example, risk of cancer of the uterus increased substantially at higher body mass index, for other cancer we saw a more modest increase in risk or no effect at all.
This variation tells us BMI must affect cancer risk through a number of different processes, depending on cancer type.
What is my risk of developing cancer if I’m overweight or obese?
The risk is greater the more weight you gain and the longer you are overweight for. But that doesn’t mean the damage is done. You can help stack the odds against cancer by avoiding gaining more weight.
Evidence is growing to show risk can start to go back down with weight loss. Plus the best ways to lose weight for most people are by eating healthily and moving more which on their own reduce cancer risk.
So the good news is that there are ways to address the problem before the damage is done!
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What leads to people being overweight or obese?
Simply put, obesity is the result of taking in more calories through your diet than you are burning through physical activity.
The reasons for this calorie imbalance vary from person to person. It can sometimes be linked to the genes we were born with, or our environments, as well as our individual behaviour and choices. And some drugs and diseases can also contribute to weight gain.
“Most people can reach and stay within a healthy weight range by eating healthily, eating smaller amounts and becoming more active. “
How could obesity lead to cancer?
It’s very clear that there is a link between cancer and obesity. But it’s still not completely understood how exactly obesity causes cancer. Research so far has identified three leading explanations. It’s helpful to start by knowing what fat is, and what it does in the body.
Fat in the body has two main functions. It acts as a store of energy. And it’s constantly spreading information and instructions to the rest of your body. These messages affect things like cell growth, chemical reactions in cells, and the body’s reproductive cycles.
So fat doesn’t just sit there doing nothing. It’s active, telling your cells what to do. And if there is too much fat in the body, then the signals it sends around the body can cause damage. It’s likely that this is how obesity raises the risk of cancer.
Growth hormones- too much body fat can cause levels of insulin and other growth factors to rise, which can tell cells to divide more often. This raises the chance that cells will change and lead to cancer.
Inflammation- when there are more fat cells in the body, specialised immune cells go to the area, possibly to remove dead and dying fat cells. They release a cocktail of chemicals called cytokines, which can lead to inflammation. This makes cells divide faster, and when this happens over a long time it can raise the risk of cancer.
Sex hormones- after the menopause, oestrogen made by fat cells can make cells divide faster in the breasts and womb (two of the cancer types most closely linked to obesity), increasing the risk of cell faults and cancer.
Belly fat has harmful effects
When too much fat is carried around the belly, it can do even more damage. So-called ‘apple’ shapes are linked to bowel, kidney, oesophageal, pancreatic, and breast cancers.
It isn’t clear exactly why this is, but it could be to do with how quickly certain chemicals from fat can get into the blood.