US researchers have found obesity is linked to as many as seven different types of cancer. Conversely those who lose weight could reduce the chances of developing the disease.
Researchers at the Washington University School of Medicine analysed data from around the world on obesity, weight gain and weight loss in relation to cancers of the breast, pancreas, kidney, colon, prostate, oesophagus and endometrium, which is the lining of the womb. The findings are published in the British Journal of Cancer this week.
In the study, weight gain seemed to have the clearest link to breast cancer in postmenopausal women. The risk of catching the disease increased by five per cent with every five kilograms of weight gained.
Weight gain in adulthood accounts for almost a quarter of cases of the disease in older women, the study found. Around 45,000 cases of breast cancer are diagnosed each year in the UK, eighty per cent of which are in women over the age of 50. And women who lost weight were at a significantly lower risk of the disease. Researchers believe this may be because weight loss lowers oestrogen levels.
Research into colon cancer found that men who put on six kilograms or more in weight ran twice the risk of contracting the disease as men who lost two kilograms or more. Those who gained 21 kilograms or more after reaching the age of 20 had a 60 per cent increased risk compared to men who have gained less than five kilograms.
Colon cancer is diagnosed in more than 36,000 people a year in the UK. Scientists suspect that weight loss and increased activity reduces circulating levels of insulin which may help to prevent the cancer from developing.
The study found links between cancer rates and increases in body mass index (BMI), the measurement of obesity which is calculated by dividing a person's weight in kilograms by their height in metres.
A BMI increase of one, after the age of 20, gives a 14 per cent increased risk of oesophageal cancer, which is diagnosed in around 7,500 Britons a year. Those with a BMI increase of more than eight ran a threefold risk of contracting the cancer.
A person whose BMI increases by five runs a 14 per cent increased risk of pancreatic cancer, a 31 per cent increased risk of kidney cancer, and, among women, a 52 per cent increased risk of endometrial cancer.
Links between prostate cancer and obesity were less clear. However, men who put on more than 10 per cent of their body weight and had a BMI greater than 24.4 were twice as likely to develop prostate cancer as men with a lower BMI.
Ed Yong, health information manager at Cancer Research UK said: "Most people associate high body weight with conditions like diabetes and heart disease, and a lot of people are not aware of the links between body weight and cancer.
"This is a very important and growing issue. Maintaining a healthy body weight is one of the most important things you can do to prevent cancer after not smoking.
"If you look at these cancers, they include two of the most common, breast and colon, and some which have very low survival rates, pancreatic and oesophagus. So body weight has a substantial impact on cancers that are common and those that are difficult to treat."