Bodyweight and risk of cancer in the UK

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The best evidence for a relationship between cancer and excess bodyweight is for cancers of the endometrium, kidney, oesophagus and gastric cardia (adenocarcinoma), colon, breast cancer in post-menopausal women, gallbladder and pancreas. Figure 2.1 shows the proportions of some of these cancers caused by being overweight or obese. 2,13, 14

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Obesity increases the risk of developing endometrial cancer by two to four-fold and the risk increases linearly with increases in BMI above 25 3. Obesity also increases the risk of breast cancer in post-menopausal women by up to 30%. 4, 5,13By contrast, pre-menopausal women with a BMI of 31 or more have been shown to have a 46% reduced risk of breast cancer, compared with women whose BMI is less than 21. 5 This risk reduction may be because obesity can disrupt ovulation 6.

A likely mechanism for the increased risk for breast and endometrial cancer in overweight women is that fatty tissue alters the levels of sex steroids. In men and post-menopausal women, fatty tissue is a major site for synthesis of oestrogens. Obesity can also increase concentrations of oestradiol in the plasma by reducing levels of sex-hormone binding globulin caused by higher insulin production and insulin-like growth factor I activity. Breast cancer risk is also affected by age at menarche and height, both of which are influenced by bodyweight earlier in life 6.

The risk of colon cancer increases by about 25% in overweight men and by about 50% in obese men compared to men with a BMI under 25. 15. The link between overweight and colon cancer is weaker in women, with risk increasing by 9% for a 5-point increase in BMI. 16. Central obesity may be a better indicator for colon cancer risk than BMI, with the European Prospective Investigation into Cancer and Nutrition showing similar risk increases in men and women, of up to 50%, for having a higher waist circumference or waist-to-hip ratio. 17 It has been shown that high levels of physical activity can reduce or remove the effect of obesity on the risk of colon cancer 7.

Risk of renal cell cancer increases by 24% in men and 34% in women with a 5-point increase in BMI, risk of oesophageal adenocarcinoma by approximately 50% in men and women and risk of gallbladder cancer by 59% in women, but not in men, for the same increase in BMI. 16.

Two recent large prospective studies in America support an association between obesity and pancreatic cancer, and a meta-analysis showed a 19% risk increase for obese individuals. 9, 10,20. Other cancers that have been linked with BMI in at least one meta-analysis include liver, thyroid, leukaemia, multiple myeloma and ovarian. 13,16,18, 19,21

In Britain, a total of 67% of men and 52% of women have a BMI of 25 or more: this includes 25% of men and 20% of women who are obese ( Figure 2.211) 12.

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In the last ten years there have been significant increases in levels of overweight and obesity 11. One in ten British men and one in four British women report dieting to lose weight 12. Trends among children and young people suggest that we are yet to experience the full health impact of the overweight and obesity epidemic in the UK.

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