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Cancer is more likely in obese women than in women of average weight

BMJ 2005; 331 doi: https://doi.org/10.1136/bmj.331.7512.310-b (Published 04 August 2005) Cite this as: BMJ 2005;331:310
  1. Roger Dobson
  1. Abergavenny

    Women who are obese are up to 36% more likely to develop cancer those of a healthy weight.

    Almost one in 14 cancers in women are due to overweight and obesity and are therefore avoidable, concludes research that looked at nearly 70 000 people in Sweden. The study has been published online ahead of print publication in the International Journal of Cancer (www3.interscience.wiley.com, doi: 10.1002/ijc.21354).

    “In women, up to 7% of all cancers in the county are attributable to overweight and obesity, with a larger effect on endometrial (up to 30%), colon (20%) and ovarian (22%) cancers. Up to 18% of melanoma cases among women and 30% of kidney cancers in men could also be attributed to BMI [body mass index] above the normal range,” write the authors, from the International Agency for Research on Cancer and universities in Sweden and the United States.

    In the research, which was partly funded by the World Cancer Research Fund and the Swedish Cancer Society, the authors used data on 35 362 women and 33 424 men recruited between 1985 and 2003 for whom health and weight measurements were available. The number of cases of cancer identified was 2691.

    The results show that women with a BMI >27.1 had a 29% higher risk than women with a BMI between 18.5 and 22.2 of developing any malignancy. When smokers were excluded, the risk was higher by 47%. Obese women (BMI >30) had a 36% higher risk of cancer than women whose BMI was between 18.5 and 25.

    Individual cancer sites most strongly related to obesity were the endometrium (the relative risk for women in the top quartile of BMI was 3.53 (95% confidence interval 1.86 to 7.43)), ovaries (relative risk 2.09 (1.13 to 4.13)), and colon (relative risk 2.05 (1.04 to 4.41)). The relative risk of obese women developing malignant melanoma was 2.55, compared with women of normal weight.

    “In women, a positive association between BMI and overall cancer risk emerged, mainly driven by the strong effects of elevated BMI on the incidence of endometrial, ovarian and colon cancers as well as melanoma,” the authors wrote.

    “This remarkably strong adverse effect of BMI on risk of endometrial cancer is believed to be due to alterations in the synthesis of sex steroids caused by increased body adiposity: both obesity and endometrial cancer risk have been associated with decreased synthesis of progesterone in premenopausal women and with increased circulating oestrogens after menopause.”

    In men no association between BMI and overall cancer risk was shown. This was probably due to the numbers of prostate and respiratory tract cancers, which accounted for more than 40% of all malignancies. Obese men were, however, at a higher risk of developing kidney cancer (relative risk 3.63 (1.23 to 10.7)) and—after cases diagnosed within one year of recruitment were excluded—colon cancer (relative risk 1.77 (1.04 to 2.95)).

    The authors point out that 12% of the men and women in the study were obese, a considerably lower proportion than in the general population in a number of countries, including the United Kingdom and the United States.

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