Obesity and colon and rectal cancer risk: a meta-analysis of prospective studies.
BACKGROUND
Whereas obesity has been associated with an increased risk of colon cancer in men, a weak or no association has been observed in women. Results for rectal cancer have also been inconsistent.


OBJECTIVE
The objective was to perform a meta-analysis to summarize the available evidence from prospective studies on the associations of overall and abdominal obesity with the risk of colon and rectal cancer.


METHODS
We searched MEDLINE (1966-April 2007) and the references of the retrieved articles. Study-specific relative risks (RRs) were pooled by using a random-effects model.


RESULTS
Thirty prospective studies were included in the meta-analysis of body mass index (BMI; in kg/m(2)). Overall, a 5-unit increase in BMI was related to an increased risk of colon cancer in both men (RR: 1.30; 95% CI: 1.25, 1.35) and women (RR: 1.12; 95% CI: 1.07, 1.18), but the association was stronger in men (P < 0.001). BMI was positively associated with rectal cancer in men (RR: 1.12; 95% CI: 1.09, 1.16) but not in women (RR: 1.03; 95% CI: 0.99, 1.08). The difference in RRs between cancer sites was statistically significant (P < 0.001 in men and P = 0.04 in women). Colon cancer risk increased with increasing waist circumference (per 10-cm increase) in both men (RR: 1.33; 95% CI: 1.19, 1.49) and women (RR: 1.16; 95% CI: 1.09, 1.23) and with increasing waist-hip ratio (per 0.1-unit increase) in both men (RR: 1.43; 95% CI: 1.19, 1.71) and women (RR: 1.20; 95% CI: 1.08, 1.33).


CONCLUSIONS
The association between obesity and colon and rectal cancer risk varies by sex and cancer site.
Larsson
Susanna C
SC
Division of Nutritional Epidemiology, National Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden. susanna.larsson@ki.se
Wolk
Alicja
A
D050153:Abdominal Fat; D000328:Adult; D000368:Aged; D050218:Body Fat Distribution; D015992:Body Mass Index; D003110:Colonic Neoplasms / Q000453:epidemiology* / Q000209:etiology* / Q000473:pathology; D015986:Confounding Factors, Epidemiologic; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009765:Obesity / Q000150:complications* / Q000473:pathology; D015995:Prevalence; D011446:Prospective Studies; D012004:Rectal Neoplasms / Q000453:epidemiology* / Q000209:etiology* / Q000473:pathology; D018570:Risk Assessment; D012307:Risk Factors; D012737:Sex Factors; D049629:Waist-Hip Ratio