Researchers have analyzed 21 previous studies that have investigated whether a link exists between ovarian cancer and the consumption of milk products and lactose. This meta-study, published in the International Journal of Cancer, has found some evidence for the hypothesis that a high intake of milk products is associated with an increased cancer risk. A possible link between milk products and ovarian cancer was first reported in 1989, and since then, many studies have further examined the possibility of a relationship. Conclusive results however, proved elusive. The studies often yielded conflicting conclusions, preventing a detailed understanding of the relationship.
Now, researchers led by Susanna C. Larsson of the Karolinska Institute in Sweden, have conducted a meta-analysis of all the previous relevant studies. The researchers looked at studies that offered data from a case-control, or cohort study on the association between intakes of milk, yogurt, cheese or lactose, and the incidence of or mortality from ovarian cancer. They also chose to examine only those studies that presented the results as an odds ratio, or relative risk. The researchers then performed a meta-analysis to determine associations between milk product consumption and cancer risk.
Differences in the studies soon became apparent, as cohort studies may record dietary practices decades before illness occurs, while case-control studies assess diet around the time of diagnosis.
The meta-analysis found notable differences between the two types of study. Case-control studies showed that low-fat milk was negatively associated, but whole milk consumption was positively associated with ovarian cancer risk.
The cohort studies indicated that a high intake of milk may increase the risk of ovarian cancer. They also revealed a 13 percent increase in ovarian cancer risk with a daily increase of 10 grams of lactose, the approximate amount in one glass of milk. In combination, the two types of studies suggested that yogurt and cheese consumption were not associated with an increase in risk.
"Prospective cohort studies, but not case-control studies, support the hypothesis that high intakes of dairy foods and lactose may increase the risk of ovarian cancer," concluded the researchers.
