Milk may reduce risk of bowel cancer: Study

By Dr. Ananya Mandal, MDJan 17 2011

Research by Associate Professor Brian Cox and Dr Mary Jane Sneyd of the Otago University’s Hugh Adam cancer epidemiology unit has shown that New Zealand schoolchildren who drank milk daily significantly reduced their chances of getting bowel cancer as adults.

The team looked at the school milk program (1937-67) that was abandoned and the reduced risk of developing bowel cancer in men and women born in New Zealand between 1941 and 1956. The study was published on Monday in the American Journal of Epidemiology showing that risk of bowel cancer was 30 per cent lower in people who drank their school milk daily. Data showed that although New Zealand has one of the highest rates of colorectal cancer in the world, the incidence in those born from about 1938 to 1953 is about 50 per cent lower than in those of earlier generations. School milk was provided free in many schools from 1937 to 1967 and Cox said that before that time, while people consumed milk in other ways, it was not commonly considered a drink. But in Southland, where many schools withdrew from the program in 1950, researchers noted that people who went to school only in Southland had about twice the risk of people from the rest of the country, though Cox said it could not be assumed that this was entirely related to school milk consumption.

They speculated that the calcium in diet could protect from certain types of bowel cancer. The study received $31,072 from the Genesis oncology trust to see if children who received free school milk, that provides about 75 per cent of the daily calcium requirement for many children, had lower rates of bowel cancer.

Cox enthused over the results and speculated similar further studies could confirm these results. He explained that the best risk reduction was seen in those who drank 1200 or more half-pint (about 300ml) bottles of milk in their school years. The team studied a total of 562 people aged 30 to 69 diagnosed with bowel cancer and compared them with 571 people of similar age without the disease. They questioned all of these people on their diet including the regular intake of dairy products taken as children. No dietary or alcohol consumption data for adulthood was noted.

Explaining further Professor Cox said that pre-cancerous growths were thought to develop in the colon really early in life and it was possible the calcium in school milk reduced the development of that early phase of the disease, lowering the lifetime risk. They write, “Although calcium supplementation in adults has been shown to reduce the risk of recurrent adenoma, the effect of childhood dietary calcium on their initial development is not known.”

Cox added, “The research team is currently planning further research which, if funding can be obtained, could confirm that the provision of milk at school can significantly reduce the risk of bowel cancer in future generations… It’s not clear how much changing your diet in adulthood would change your risk of bowel cancer.”