Milk and Ovarian Cancer - Is There a Link?

Summarized by Robert W. Griffith, MD
September 26, 2005

Introduction

A possible connection between drinking milk and ovarian cancer was first proposed in 1989. Since then, many studies of different nutritional lifestyles have been done, but results are conflicting. In an effort to resolve this, Swedish researchers have conducted a meta-analysis of relevant studies. (A meta-analysis uses statistical methods to combine the results from numerous clinical studies to decrease the uncertainty of an overall result.) Their findings have been published in the International Journal of Cancer, and are summarized here.

What was done

Two types of studies were considered in the analyses: case-control studies (in which patients with cancer of the ovary were compared with one or more carefully matched persons without cancer), and cohort studies (in which a large group of persons are examined over a period and those with ovarian cancer are compared with those without cancer). Studies used had to meet certain strict criteria. Twenty-one studies (18 case-control and 3 prospective cohort studies) were eligible for inclusion in the analysis.

The nutritional factors studied were the intake of milk, yogurt, cheese, and lactose. The relative risk (RR) of contracting ovarian cancer was calculated for different levels of intake of these dairy products.

What were the results?

In the 18 case-control studies, there was no evidence of a link between dairy food and lactose intake and ovarian cancer, except for whole milk intake. The RR for highest whole milk intake vs. lowest whole milk intake was 1.27; i.e. those in the highest whole milk category had a 27% higher risk of ovarian cancer.

The 3 cohort studies were large and well-controlled. There was a consistent and significant link between intakes of total dairy foods, low-fat milk, and lactose and the risk of ovarian cancer. For every 10 gram daily increase in lactose (equal to about one glass of milk) there was a 13% increase in the risk of cancer of the ovary. Two of these studies showed that the association between lactose and ovarian cancer was confined to one type - serous cancer of the ovary.

In neither group of studies was yogurt or cheese linked to an increased risk of ovarian cancer.

What do these findings mean?

First, we need to try to explain the difference between the findings for the two types of study. Because the case-control studies estimated dietary intake after the cancer had been diagnosed, they might have been affected by 'recall bias'. And case-control studies usually assess recent dietary intake, whereas cohort studies usually measure intake at the start of the study period.

Second, how could eating more dairy products affect cancer occurrence? It's been speculated that there's an increase in hormone intake affecting the ovarian tissue. Alternatively, lactose breaks down into galactose and glucose, and galactose may have a specific toxic effect on certain ovarian cells.

The fact that one cell type of ovarian cancer (those with serous cells) showed an association with lactose intake receives support from another study that shows a protective effect of physical activity on this type of ovarian cancer.¹ Future research should concentrate, therefore, on determining the specific type of ovarian cancer that's open to influence by lifestyle changes. In the meantime, the nutritional benefits of milk - if it's not full-cream milk - should not be disregarded. As with all things, take dairy products in moderation. Don't forget that calcium, which is found in milk, may reduce the risk for a much more common cancer - colorectal cancer (see the last link below).

Source

• Larsson SC, Orsini N, Wolk A. Milk, milk products and lactose intake and ovarian cancer risk: A meta-analysis of epidemiological studies. Int J Cancer 2005 July 28; [Epub ahead of print] - accessed 9/10//05

Footnotes
1. Physical activity and the risk of ovarian cancer: A case-control study in Canada. SY. Pan, AM. Ugnat, Y. Mao,  et al., Int J Cancer, 2005, vol. 117, pp. 300--307

Related Links
Ovarian Cancer - Making the Diagnosis in Time
Good Health Habits Cut Cancer Risk
Calcium May Reduce Colon Cancer Risk in Men

Please take a moment to give us your comments. For questions about Health matters you may check our "Questions & Answers" Portal and Service.