Obesity Linked To Several Cancers

The risk of many different kinds of cancers, both common and less common, has been linked to an increased body mass index (BMI.) This risk can vary between sexes and ethnic groups, depending on the type of cancer, as published in the February 16, 2008 issue of The Lancet.

Increased bodyweight is ever more recognised as a risk factor for many common cancers. This can be seen in overweight patients (BMI of 25-29.2 kg/m2) as well as obese patients (BMI of 30 kg/m2 or more.) To examine this, Dr. Andrew Renehan, of the University of Manchester and Christie Hospital of the NHS
Foundation Trust, Manchester, UK, and colleagues performed a meta-analysis, combining 221 datasets including 282,137 cases from previous studies.

They determined the risk of cancer associated with a 5 kg/m2 increase in BMI. This appeared to increase the risk of specific types of cancers in gender specific situations:

In men, the risk of oesophageal adenocarcinoma was increased by 52 percent, thyroid cancer by 33 percent, and colon and kidney cancers each by 24 percent.
In women, the risk of endometrial cancer was increased by 59 percent, gallbladder cancer by 59 percent, oesophageal adenocarcinoma by 51 percent and kidney cancer by 34 percent.
In men, weaker but significant increases in risk were associated with rectal cancer and malignant melanoma.
In women, weaker but significant increases in risk were associated with postmenopausal breast, pancreatic, thyroid, and colon cancers.
In both sexes, weaker but significant increases in risk were associated with leukaemia, multiple myeloma, and non-Hodgkin's lymphoma.
The association for colon cancer was stronger in men than in women (24 percent versus 9 percent.) When studies from North America, from Europe and Australia, and from the Asia-Pacific region were compared, similar associations were found. However, studies from the Asia-Pacific region showed a stronger association between the increased BMI and both premenopausal and postmenopausal breast cancers. These findings echo those reported last year by the World Cancer Research Fund as well as those published in November 2007 by the UK Million Women's study team.

The authors conclude with a summary of their results and future directions for research. "Increased BMI is associated with increased risk of common and less common malignancies. For some cancer types, associations differ between sexes and populations of different ethnic origins. These epidemiological observations should inform the exploration of biological mechanisms that link obesity with cancer."

Dr Susanna Larsson and Professor Alicja Wolk, Division of Nutritional Epidemiology, National Institute of Environmental Medicine, Karolinska Institute, Stockholm, Sweden, commented in an accompanying piece: "The number of deaths per year attributable to obesity is about 30 000 in the UK and ten times that in the USA, where obesity has been estimated to have overtaken smoking in 2005 as the main preventable cause of illness and premature death."

They conclude: "Efforts will be needed to increase education on diet and physical activity, train health professionals, restrict advertisements of high-calorie and low-nutrient foods, limit access to unhealthy foods in schools and workplaces, levy taxes on sugary drinks and other foods high in calories, fat, or sugar, lower the prices of health foods, and promote physical activity in schools and workplaces. National cancer plans should include all these factors to reduce obesity, and thus decrease cancer incidence and increase survival."

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, Marcel Zwahlen
The Lancet, Vol 371, February 16, 2008

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