School milk and risk of colorectal cancer: a national case-control study.

To determine whether school milk consumption in childhood decreased the risk of adult colorectal cancer, the authors conducted a national population-based, case-control study of 562 cases and 571 controls. The authors identified new cases of colorectal cancer in 2007 among people aged 30-69 years from the New Zealand Cancer Registry. Controls were randomly selected from the electoral rolls and frequency matched to cases in 5-year age groups. Participation in school milk programs was associated with a reduced odds ratio for colorectal cancer (odds ratio (OR) = 0.70, 95% confidence interval (CI): 0.51, 0.96). Odds ratios decreased with increasing numbers of bottles of milk drunk compared with no school milk (for 1-799 bottles, OR = 1.04, 95% CI: 0.66, 1.67; for 800-1,199 bottles, OR = 0.81, 95% CI: 0.51, 1.29; for 1,200-1,599 bottles, OR = 0.62, 95% CI: 0.41, 0.93; for 1,600-1,799 bottles, OR = 0.57, 95% CI: 0.37, 0.90; and for 1,800 or more bottles, OR = 0.62, 95% CI: 0.41, 0.96). Participation in school milk programs in New Zealand was associated with a 2.1% reduction (95% CI: 0.7, 3.5) in the odds ratio for colorectal cancer for every 100 half-pint bottles drunk (1 half-pint bottle = 284 mL).