Obesity and risk of colorectal cancer: a meta-analysis of 31 studies with 70,000 events.
BACKGROUND
Colorectal cancer is the second most common cause of death and illness in developed countries. Previous reviews have suggested that obesity may be associated with 30% to 60% greater risk of colorectal cancer, but little consideration was given to the possible effect of publication bias on the reported association.


METHODS
Relevant studies were identified through EMBASE and MEDLINE. Studies were included if they had published quantitative estimates of the association between general obesity [defined here as body mass index (BMI) > or = 30 kg/m(2)] and central obesity (measured using waist circumference) and colorectal cancer. Random-effects meta-analyses were done, involving 70,000 cases of incident colorectal cancer from 31 studies, of which 23 were cohort studies and 8 were case-control studies.


RESULTS
After pooling and correcting for publication bias, the estimated relative risk of colorectal cancer was 1.19 [95% confidence interval (95% CI), 1.11-1.29], comparing obese (BMI > or = 30 kg/m(2)) with normal weight (BMI <25 kg/m(2)) people; and 1.45 (95% CI, 1.31-1.61), comparing those with the highest, to the lowest, level of central obesity. After correcting for publication bias, the risk of colorectal cancer was 1.41 (95% CI, 1.30-1.54) in men compared with 1.08 (95% CI, 0.98-1.18) for women (P(heterogeneity) <0.001). There was evidence of a dose-response relationship between BMI and colorectal cancer: for a 2 kg/m(2) increase in BMI, the risk of colorectal cancer increased by 7% (4-10%). For a 2-cm increase in waist circumference, the risk increased by 4% (2-5%).


CONCLUSIONS
Obesity has a direct and independent relationship with colorectal cancer, although the strength of the association with general obesity is smaller than previously reported.
Moghaddam
Alireza Ansary
AA
The George Institute for International Health, Sydney, Australia.
Woodward
Mark
M
Huxley
Rachel
R
D015992:Body Mass Index; D016022:Case-Control Studies; D015331:Cohort Studies; D015179:Colorectal Neoplasms / Q000453:epidemiology* / Q000209:etiology*; D005260:Female; D006801:Humans; D008297:Male; D009765:Obesity / Q000150:complications*; D012307:Risk Factors; D049629:Waist-Hip Ratio