This meta-analysis, published this week in The Lancet confirms that excess body weight, whether simply overweight (by body mass index, BMI) or obese, has a real association with an increased risk of various cancers - common and less common.
It has increasingly been recognised that a high BMI is linked to an excess risk of cancer. However, the studies that have been done so far make it difficult to compare associations across studies, populations and cancer sites. The World Cancer Research Fund report of 2007 showed that a high BMI is linked to an increased risk of oesophageal adenocarcinoma, and with cancers of the pancreas, colorectum, postmenopausal breast, endometrium, and kidney. This meta-analysis aimed to pull out the associations across cancer sites and between sexes and different populations to quantify the risk of different cancers associated with an incremental increase in BMI.
The authors analysed 141 articles, that included 282 137 cases of various cancers. In men, a 5 kg/m2 increase in BMI was strongly associated with oesophageal adenocarcinoma and with thyroid, colon, and renal cancers. In women, they recorded strong associations between a 5 kg/m2 increase in BMI and endometrial, gallbladder, oesophageal adenocarcinoma, and renal cancers. They found weaker positive associations between increased BMI and rectal cancer and malignant melanoma in men; postmenopausal breast, pancreatic, thyroid, and colon cancers in women; and leukaemia, multiple myeloma, and non-Hodgkin lymphoma in both sexes. Associations were stronger in men than in women for colon cancer. Associations were generally similar in studies from North America, Europe and Australia, and the Asia–Pacific region, but we recorded stronger associations in Asia–Pacific populations between increased BMI and premenopausal and postmenopausal breast cancers.
This study differs from other similar studies in that it has found associations between raised BMI and the less common cancers and differences between risks in men and women, particularly for colon cancer. The finding of a particularly high association between breast cancer and BMI among Asian-Pacific women needs further research and investigation, according to the authors.
Recognising the problems inherent in using BMI as a measure of fatness, rather than body weight (made up of fat and muscle), the authors also suggest that waist circumference may, in fact be a better measure of actual fatness in terms of increased cancer risk. It is excess body fat that appears to lead to the increases in cancer risk - body weight can be high in athletic people because of a high ratio of muscle to fat.
