Hi,
I have reviewed the two articles (The Multiethnic Cohort Study and the NIH-AARP Diet and Health Study) in the
American Journal of Epidemiology [Dec. 2007, 166(11): 1259-69; 1270-79] from which the information regarding
the association between non-fat milk and prostate cancer comes from. Both articles involve studies which are
called “cohort studies”. I would just like to explain something about the nature of these studies so that you
may better understand what the results mean. From the way you asked your questions, I am under the impression
that the study results may have been misinterpreted.
A cohort study involves a group of people (cohort) sharing a common characteristic, who are observed over a
certain period of time for the appearance of the disease of interest. In the case of the two articles I
mentioned, both involved a large group of men (roughly 80,000 and 300,000 subjects) whose diet were
characterized at the onset using a detailed quantitative food frequency questionnaire. The men were followed
through a period of 6-8 years and those who developed prostate cancer during the period of observation were
identified, and their diet analyzed.
Both studies found that there is no association between an increased risk of prostate cancer and total amount
of milk consumed as well as the consumption of dairy products in general. The NIH-AARP study (the larger and
more significant of the two) even concludes that the findings “do not provide strong support for the
hypothesis that calcium and dairy foods increase prostate cancer risk”.
On the other hand, both studies found that low fat and skim milk, but not other dairy foods, was associated
with an increased risk of advanced prostate cancer (23 % increase in risk relative to those who do not consume
skim milk at all). What should be noted in the above result is that the relationship between low fat milk
intake and prostate cancer is merely an ASSOCIATION and NOT CAUSATION. Both studies do not prove that drinking
non-fat milk causes the risk for prostate cancer to increase. The results merely state that more prostate
cancer cases tend to be seen among those who drink more low fat milk, but for all we know, the intake of low
fat milk is just an INCIDENTAL finding among men with prostate cancer, and is not the cause.
So my advice is: you may continue drinking low fat milk to your heart’s content. The present evidence is not
compelling enough to ban skim milk from older men’s diets.
