Writing in American Journal of Epidemiology scientists from University of Otago Medical School wanted to find out if participation in the New Zealand milk-in-schools program had led to the decreased rates of colon cancer.
From 1937 to 1967, the government-funded program provided 1 half-pint (284 ml) bottle of full-cream milk free each day to the majority of school children in New Zealand. The generations in New Zealand who participated in the milk-in-schools program were born from 1932 to 1962.
According to the scientists, previous research suggested that calcium intake for adults can reduce the risk of recurrent adenoma, a benign tumor that has a glandular origin. However the researchers said the effect of childhood dietary calcium intake on their initial development is currently unknown.
The findings suggest that participation in school milk programs was associated with 30 per cent lower chance of getting bowel cancer.
Results were more significant for those who consumed more milk. A 2.1 per cent reduction was reported in the odds ratio for every 100 half-pint of bottles drunk at school.
The researchers claim that the calcium in milk can prevent the development of adenoma through mechanisms such as the protection from toxic bile acids and promotion of cellular differentiation.
Some adenomas are thought to develop in young adulthood, and their prevalence increases with age, according to the scientists.
“Further etiologic studies of colorectal cancer should examine the effects of childhood milk consumption or calcium intake, and childhood diet overall, in addition to adult diet. In addition, the biologic mechanisms by which childhood milk consumption may reduce risk of colorectal cancer should be explored,” said the researchers.
Methodology and results
The study compared 562 cases and 571 controls. Each was randomly selected from the electoral rolls and frequency matched to cases in 5-year age groups.
Each participant was questioned on their health and lifestyle habits. The subjects were also asked about their previous school milk participation and other childhood milk consumption and dietary preferences, including the total quantity they drunk per week.
Significantly reduced adjusted odds ratios were found for all three measures of school milk consumption for those without a history of ulcerative colitis or Crohn’s disease and for those born in New Zealand.
A significant reduction in the risk of colorectal cancer with increasing frequency of consumption of dairy products other than school milk from the ages of 5–12 years was observed, but not from ages 13–18 years.
Source: American Journal of Epidemiology
Published online ahead of print: doi:10.1093/aje/kwq390
School Milk and Risk of Colorectal Cancer: A National Case-Control Study
Authors: B. Cox and M. J. Sneyd