An analysis of 21 studies that have investigated the link betweenovarian cancer and the consumption of milk products and lactose hasfound some support for the hypothesis that high intake is associatedwith increased cancer risk. The results of this analysis, publishedonline August 5, 2005 in the International Journal of Cancer, theofficial journal of the International Union Against Cancer (UICC),found that support was stronger in cohort studies, compared tocase-control studies, which offered varying results. The article isavailable via Wiley InterScience at http://www.interscience.wiley.com/journal/ijc.
Since a positive correlation between ovarian cancer risk and theconsumption of milk products and lactose was first reported in 1989,many epidemiological studies have further examined the relationship.However, these studies have yielded conflicting conclusions. To betterunderstand the uncertain relationship, researchers led by Susanna C.Larsson of the National Institute of Environmental Medicine at theKarolinska Institute in Sweden, conducted a meta-analysis of relevantcase-control and cohort studies.
The researchers sought reports that offered data from acase-control, or cohort study on the association between intakes ofmilk, yogurt, cheese or lactose, and incidence of or mortality fromepithelial ovarian cancer. Studies also had to present results as anodds ratio, or relative risk, with 95 percent confidence intervals. Theresearchers accepted three prospective cohort studies, and 18case-control studies and performed a meta-analysis to determineassociations between consumption and cancer risk.
Their analysis found notable differences between case-controland cohort studies. Case-control studies showed low-fat milkconsumption negatively associated, and whole milk consumptionpositively associated, with the risk of ovarian cancer, but offered nosupport for the involvement of lactose in the development of ovariancancer. By contrast, prospective cohort studies indicated that highintakes of milk may increase the risk of ovarian cancer. They alsorevealed a 13 percent increase in ovarian cancer risk with a dailyincrease of 10 grams of lactose, the approximate amount in one glass ofmilk. When case-control and cohort studies were considered incombination, yogurt consumption was associated with a non-significantincrease in cancer risk, while cheese was not associated with risk.
The differences between the findings of case-control studiesand those of cohort studies could be explained by a number of factors:selection bias, recall bias or changes in dietary practices aftercancer diagnosis. They might also be due to the time interval betweendiet assessment and illness, since cohort studies may record dietarypractices decades before illness occurs, while case-control studiesassess diet around the time of diagnosis. Other limitations of thisstudy include the observational nature of the assessed studies,imprecise measurements of diet, and publication bias.
Of note, the two studies that examined histological subtypesof ovarian cancer found that the associations with milk and lactoseintakes were confined to serous ovarian cancer, leading researchers toadvise, "future studies should consider specific subtypes of ovariancancer, and the interrelationship between intakes of dairy foods andlactose, genetic polymorphisms, and ovarian cancer risk."
"In conclusion," they write, "prospective cohort studies, butnot case-control studies, support the hypothesis that high intakes ofdairy foods and lactose may increase the risk of ovarian cancer."
Article: "Milk, Milk Products, and Lactose Intake and Ovarian CancerRisk: A Meta-Analysis of Epidemiological Studies." Susanna C. Larsson,Nicola Orsini, and Alicja Wolk, International Journal of Cancer;Published Online: August 5, 2005 (DOI: 10.1002/ijc.21305).
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