Most people know that being overweight increases your risk of developing diseases such as diabetes and heart disease. What a lot of people don’t realise however is that being overweight also increases your risk of developing many forms of cancer.
The most comprehensive study on the environmental and lifestyle factors responsible for cancer is known as “The Cancer Prevention Study 2″. The study was conducted from 1982 to 1997 and followed 1.2 million American men and women, collecting information on their diet, medical history, weight and exercise levels among other things.
The study found that obese individuals were far more likely to develop many cancers compared to those in a healthy weight range. In men with a body mass index (BMI), the relative risk of dying from liver cancer was 4.5 times greater than those in a healthy weight range. Furthermore their risk of dying from pancreatic cancer was 2.61 times greater, their stomach cancer risk 1.94 times greater, colo-rectal cancer risk 1.84 times greater and kidney cancer risk 1.70 times greater.
In total, men with a BMI greater than 35 were at around a 40% greater risk of dying from some form of cancer when compared to men with a healthy BMI (between 18.5 and 24.9). At even higher BMI levels, cancer risks increased further, men with a BMI greater than 40 had a 52% greater risk of dying from some form of cancer compared to those in the healthy weight range. A graph of the increased cancer risks in the highest BMI category is presented below.
The results were even more dramatic in women – the risk of dying from uterine cancer was a massive 6.25 times greater in women with a BMI over 40. Kidney cancer risk was 4.75 times greater while the risks of dying from cancers of the cervix, pancreas and breast were all more than 2 times greater in women with a BMI over 40 compared to those with a healthy BMI. In total, women with a BMI over 40 had an 88% greater risk of dying from some form of cancer compared to women in the healthy weight range.
Other cancers that were shown to be more prevalent amongst obese individuals included non-Hodgkin lymphoma, prostate cancer, and bladder cancer.
So why are overweight individuals more likely to develop and subsequently die from cancer? It is possible that excess weight itself directly increases cancer risk through some mechanism. It is also possible that the lower exercise levels seen in overweight people effect cancer rates. It is known for example that colo-rectal cancer rates are lower amongst those who exercise regularly and that breast cancer risk can also be reduced by even small amounts of physical activity.
A further possibility is that overweight people are more likely to have chronic high blood sugar levels and diabetes. High blood sugar levels have been implicated in both pancreatic and liver cancer.
Whatever the reason, the evidence is compelling. Overweight individuals are much more likely to develop cancer than those in a normal weight range. If you are overweight, even a small loss in weight can increase your chances of staying cancer free by a significant amount.
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