Bodyweight and risk of cancer statistics

There is convincing evidence that being overweight or obese increases cancer risk 1. A study published in December 2011 estimated that around 17,000 cases of cancer in the UK each year are linked to people being overweight or obese. The study notes that the list of cancers considered as being related to bodyweight in this study is conservative, so the actual number of cancers due to this factor may be higher.2

section reviewed 01/06/05
section updated 01/01/12

Table 2.1 summarises what we currently know about overweight, obesity and risk of cancer.

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Body mass index (BMI) is the most commonly used measure of bodyweight. A BMI of 25-30 is overweight and a BMI of over 30 is obese.

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 these cancers in the UK in 2010 caused by being overweight or obese. 2

Figure 2.1: Proportion of cancers linked to excess body mass index (BMI), UK, 2010

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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 a meta-analysis showing a non-significant 9% increase in risk for obese women compared to women with a healthy bodyweight (BMI<25). 15. 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 non-Hodgkin lymphoma, thyroid, leukaemia, multiple myeloma and ovary. 13,16,19,21 Liver cancer has been linked with excess bodyweight in one meta-analysis,18 but not in another.16 Brain cancer has been linked with excess bodyweight in the Million Women Study.24

section reviewed 01/06/05
section updated 01/01/12

In the UK, the latest data show that a total of 69% of men and 59% of women have a BMI of 25 or more: this includes 24% of men and 32% of women who are obese. 12 In addition, 30% of boys and 31% of girls aged 2-18 in the UK are overweight or obese 12.   The proportion of men and women in England with a BMI over 25 has increased since the 1990s, as Figure 2.2 shows. 23 The proportion of adults in Scotland that are overweight or obese has increased over the same period.25

It has been estimated, based on non-linear regression of trends in BMI in England between 1993-2004, that by 2050 60% of males and 50% of females in England will be obese. Based on the same analysis, it has been estimated that, by 2021, the proportion of overweight adult men in England will be equal to the proportion of obese men – around 43% in each group, while the proportion of men with a healthy bodyweight (BMI <25) will be 13%. For women, it has been estimated that the proportion of overweight and obese adults will be equal in 2024 (both 35%), while only a quarter of adult women will have a healthy BMI. 22

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BMI is not a perfect measure of levels of overweight, especially for athletes, bodybuilders and children. However, trends in waist circumference in adults in England also show an increase in levels of overweight, as shown in Figure 2.3

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section reviewed 01/06/05
section updated 01/06/11