A UK research team reviewing data pooled from over 140 studies has found that increasing BMI (body mass index, the ratio between a person’s weight and their height squared) is linked to increasing risk of developing a number of common and some less common cancers. They also found that the link varies with gender and in some cases, by ethnic origin.
The meta-analysis was the work of Dr Andrew Renehan, Department of Surgery, School of Cancer Studies, University of Manchester, UK, and colleagues, and is published in the 16th February issue of The Lancet.
A number of studies on adults have suggested links between BMI and the risk of developing some of the more common cancers. For this study, Renehan and colleagues carried out a systematic review to determine the strengths of the links between BMI and a range of cancers, and how they varied by sex and ethnic origin.
By scanning Medline and Embase for prospective studies of incident cases published between 1966 to November 2007, they found 221 sets of data from 141 articles covering over 280,000 cases of 20 types of cancer.
Using statistical tools called random effects meta-analysis and meta-regressions, they were able to treat the data sets as if they were one collective pool and look for estimated risk for each type of cancer linked to increments of 5 kg/m2 of BMI.
The results showed that for men, a 5 kg/m2 increase in BMI was strongly linked to cancer of the:
- Throat (oesophageal adenocarcinoma, relative risk 1.52).
- Thyroid (relative risk 1.33).
- Colon (relative risk 1.24).
- Kidney (renal, relative risk 1.24).
For women, a 5 kg/m2 increase in BMI was strongly linked to cancer of the:
- Lining of the uterus (endometrial. relative risk 1.59).
- Gallbladder (relative risk 1.59).
- Throat (oesophageal adenocarcinoma, relative risk 1.51).
- Kidney (renal, relative risk 1.34).
The researchers also found weaker, but still positive, links between incremental increases in BMI and increased risk of malignant melaleukaemia, multiple myeloma, and non-Hodgkin lymphoma in both sexes, and with rectal cancer and malignant melanoma in men, and in postmenopausal breast, pancreatic, thyroid, and colon cancers in women. The link between incremental increases in BMI and colon cancer was much stronger in men than in women.
In terms of ethnic origin, Renehan and colleagues found that associations were broadly similar in studies from Europe, Australia, North America, and the Asia-Pacific Region, with one exception: the links were stronger for premenopausal and postmenopausal breast cancers in the Asia-Pacific Region.
The researchers concluded that increased BMI is linked to increased risk of both common and less common types of cancer, with some links differentiated by gender and ethnic origin. They suggested that these findings should help to explore the biological connection between obesity and cancer.
According to the World Health Organization, BMI falls into the following ranges:
– BMI less than 18.4 = underweight.
– BMI between 18.5 and 24.9 = ideal weight.
– BMI between 25 and 29.9 = overweight.
– BMI between 30 and 39.9 = obese.
– BMI over 40 = severely obese.
These figures are based on BMI being equal to a person’s weight in kilograms divided by their height in metres squared. Thus a person who weighs 70kg, and stands 1.75m tall, has a BMI of 22.9, and would be classed as having an ideal weight for their height.
People should think about losing weight if their BMI is over 25 because they risk developing severe health problems such as heart disease, obesity and cancer.
“Body-mass index and incidence of cancer: a systematic review and meta-analysis of prospective observational studies.”
Andrew G Renehan, Margaret Tyson, Matthias Egger, Richard F Heller, and Marcel Zwahlen.
The Lancet 2008; 371:569-578.
Volume 371, Number 9612, 16 February 2008.
Sources: The Lancet article, NHS Direct.
Written by: Catharine Paddock, PhD