Prostate cancer is the most common cancer among American men, with an 11.6% lifetime risk, according to the National Cancer Institute.
The United States' rate of new cases, 101.8 per 100,000 men, in 2016 was not the highest prostate cancer rate in the world—Australia and New Zealand had rates of 111.6 per 100,000 men in 2012, according to the World Cancer Report 2014—but it was far higher than the worldwide rate of 34.2 per 100,000 men.
China, Japan and India have the lowest rates, and residents of those countries also consume fewer dairy products than Americans do. Increasingly, research is finding a possible link between plant-based diets and lower risks of prostate cancer. For this study, researchers from the Mayo Clinic reviewed previous publications looking for an association between diet and prostate cancer.
“Our review highlighted a cause for concern with high consumption of dairy products,” lead author John Shin, M.D., a Mayo Clinic oncologist, said in a released statement. “The findings also support a growing body of evidence on the potential benefits of plant-based diets.”
Summary: After examining 47 studies of varies sizes, the researchers determined that most of the studies found a relationship between eating plant-based foods and a lower risk of prostate cancer; animal-based foods—especially dairy products—are associated with increased risk of prostate cancer.
The study: Researchers looked for studies published between 2006 and February 2017 that included terms such as prostate cancer, dairy products, milk, vegan and plant-based diet. After eliminating articles that did not investigate a link between diet and prostate cancer, studies were grouped by design and size for analysis.
The 47 chosen studies included 29 cohort studies of various sizes; 13 case-control studies; four meta-analyses; and one population study. The cohort studies consisted of two with 100,000 or more subjects; six with between 40,000 and 99,999 subjects; 11 with 10,000 to 39,999 subjects; and 10 with less than 10,000 subjects. All the studies examined were conducted in English and involved human participation.
The findings: Regarding vegetarian diets, two of the five cohort studies found an association between plant-based diets and lower risks of prostate cancer; three cohort studies did not find a change in the risk. Three studies involving vegan diets all found that following a vegan died lowers the risk of prostate cancer.
Researchers reviewed 12 studies, including a large population study, to look at the effect of eating meat and fish on the risk of prostate cancer. The large population study found an association between eating meat and developing prostate cancer, but two cohort studies found no effect. One case-control study found that consumption of beef, pork or lamb was linked to a lower risk of prostate cancer; two found that men who eat the most meat have a higher risk than men who eat less.
Of the 24 studies that considered an association between dairy consumption and prostate cancer, two meta-analyses, seven cohort studies and one case-controlled study found an increased risk of prostate cancer. One cohort study found a decreased risk when men consumed dairy as children. Thirteen other analyzed works did not find an association between dairy and prostate cancer.
Study conclusions: The researchers found that most studies looking at consumption of plant-based foods “showed either no significant association or an association with decreased risk” of prostate cancer. Alternately, the majority of cohort studies found increased risk or no change in risk of prostate cancer when animal-based foods, including dairy, are consumed.
“Furthermore, increased intake of calcium also appeared to be associated with increased (prostate cancer) risk. Since dairy products are rich in calcium, this raises the possibility of calcium playing an important role in the link between dairy and (prostate cancer),” the study’s authors wrote.
They added, “There does not appear to be a clear association between increased (prostate cancer) risk and increased consumption of other types of animal-based foods, including red, white, or processed meat, fish, and eggs.”
Why the research is interesting:
- The National Cancer Institute estimates that 31,620 men in the United States will die of prostate cancer this year—the second-highest mortality rate of all cancers in men.
- As Americans consume less meat and dairy products and eat more plant-based foods, mortality rates for several common cancers are decreasing, according to a 1997 study published in the Journal of the National Cancer Institute. A 1981 study estimated that 35% of cancers could be linked to diet, and a follow-up study in 2015 essentially supported those findings.
- The 47 studies reviewed here including more than 1 million participants. Researchers looked at dietary patterns as well as how subsets of foods such as fruits, vegetables, nuts and grains affected prostate-cancer risks.
Points to consider:
- Studies such as this cannot prove causation, just a relationship. Therefore, other factors—participants’ regular diets, exercise habits, smoking and drinking history—could affect the findings without the researchers’ knowledge.
- The studies reviewed here primarily collected information about participants’ diets based on the participants’ memories, which may not be as reliable as having participants keep food diaries, for example.
- Some of these studies looked at the incidence of prostate cancer, while others considered only mortality.
- The authors suggest that more randomized, controlled studies are needed to verify these findings. Research also is needed to understand the effects of other factors such as smoking and exercise on the risk of prostate cancer.
Authors: John Shin, M.D., Department of Internal Medicine and Department of Medical Oncology, Mayo Clinic, Rochester, Minnesota; Denise Millstine, M.D., Women’s Health Internal Medicine, Mayo Clinic, Scottsdale Arizona; and Barbara Ruddy, M.D., Mark Wallace, M.D. and Heather Fields, M.D., Department of Medicine, Mayo Clinic, Scottsdale, Arizona.
Published: Effect of Plant- and Animal-Based Foods on Prostate Cancer Risk, Journal of the American Osteopathic Association, October 2019.