Objective: To study whether birth size influences colorectal cancer risk in adulthood.
Design: A cohort of Norwegian men and women identified from midwives' birth records with long term cancer follow up through the Norwegian Cancer Registry.
Setting: St Olav's University Hospital, Trondheim, Norway.
Participants: 16,016 women and 19 681 men born between 1920 and 1958 and alive in 1960.
Outcome measures: Incidence rate ratios (RRs) for colorectal cancer with 95% confidence intervals (CIs) and two sided p values for trend across categories of birth dimensions.
Results: Men whose birth length was less than 51 cm had a nearly twofold higher risk of colorectal cancer (RR 1.9 (95% CI 1.0-3.7)) compared with men who were 53 cm or more, after adjustment for birth cohort, maternal age at childbearing, length of gestation, gestational hypertension or pre-eclampsia, birth order, maternal height, and indicators of maternal socioeconomic status. The association displayed a linear trend across categories of birth length (p(trend) = 0.03). Among men, similar associations were found for birth weight and head circumference, but for women there was no association between any of these birth dimensions and risk of colorectal cancer.
Conclusion: The results suggest that among men, but not women, being relatively short at birth is associated with increased risk of colorectal cancer in adulthood, indicating that intrauterine growth could be important for colorectal carcinogenesis.