A basis for this research is the correlation between Western countries where both prostate cancer rates and dairy consumption are high, and Asian countries, where both prostate cancer rates and dairy consumption are low.
In the US, the lifetime risk of prostate cancer is 11.6%. It has the highest incidence and second highest mortality rate of all cancers in men, with more than 30,000 deaths annually, according to The Journal of the American Osteopathic Association.
The researchers noted that a large epidemiologic study in 1981 estimated that 35% of all cancer could be attributed to dietary causes, and a 2015 review of the report found its estimates to be generally true in the 21st century.
For this particular journal review, the researchers analyzed 47 previous scientific journal articles on the topic that were published between 2006 and February 2017.
They found that most of the studies showed plant-based foods are associated with either decreased or unchanged risk of prostate cancer, while animal-based foods and particularly dairy products are associated with either increased or unchanged risk of prostate cancer.
Of the five prospective cohort studies that investigated the effects of a vegetarian diet, the journal said two showed an association with decreased incidence of all cancers including prostate. Three showed no change in risk. Three other studies examined vegan diets, and all found an association with decreased prostate cancer risk.
Some studies found a correlation between increased vegetable consumption and lower risk, while fruit had no effect either way. Red meat has historically been associated with cancer incidence, but five studies analyzed by the researchers showed no effect.
Most of the dairy risk lies with milk, cheese and increased calcium consumption. Butter, cream and yogurt showed a lower risk by comparison.
John Shin, MD, lead author and Mayo Clinic oncologist, said, "Our review highlighted a cause for concern with high consumption of dairy products. The findings also support a growing body of evidence on the potential benefits of plant-based diets."
Dr Shin also said that even with these patterns of association, more investigation is needed to understand the nature and strength of those associations.