Excess bodyweight, expressed as increased body-mass index (BMI), is associated with
the risk of some common adult cancers. We did a systematic review and meta-analysis
to assess the strength of associations between BMI and different sites of cancer and
to investigate differences in these associations between sex and ethnic groups.
We did electronic searches on Medline and Embase (1966 to November 2007), and searched
reports to identify prospective studies of incident cases of 20 cancer types. We did
random-effects meta-analyses and meta-regressions of study-specific incremental estimates
to determine the risk of cancer associated with a 5 kg/m2 increase in BMI.
We analysed 221 datasets (141 articles), including 282,137 incident cases. In men,
a 5 kg/m2 increase in BMI was strongly associated with oesophageal adenocarcinoma
(RR 1.52, p<0.0001) and with thyroid (1.33, p=0.02), colon (1.24, p<0.0001), and renal
(1.24, p <0.0001) cancers. In women, we recorded strong associations between a 5 kg/m2
increase in BMI and endometrial (1.59, p<0.0001), gallbladder (1.59, p=0.04), oesophageal
adenocarcinoma (1.51, p<0.0001), and renal (1.34, p<0.0001) cancers. We noted weaker
positive associations (RR <1.20) 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 (p<0.0001) 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 (p=0.009) and postmenopausal (p=0.06) breast cancers.
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.