Dairy, plant-based food consumption may impact risk for prostate cancer
Consumption of high amounts of dairy products appeared to be associated with increased risk for prostate cancer, according to results of a retrospective study published in The Journal of the American Osteopathic Association.
Eating high amounts of plant-based foods, however, may reduce prostate cancer risk, researchers found.
“The mechanism for the link between dairy and prostate cancer is not certain, but one hypothesis has to do with calcitriol, the hormonal form of vitamin D,” John Shin, MD, oncologist at Mayo Clinic in Rochester, Minnesota, told HemOnc Today. “It has been shown that calcitriol inhibits prostate cancer cell growth and that increased calcium intake lowers levels of calcitriol in the body. Because dairy products are rich in calcium and serve as the primary source of calcium for many people in Western countries, it stands to reason that dairy might be linked to prostate cancer risk in this way.”
Shin added that there is probably more than one reason for this association, including the fact that dairy consumption raises concentrations of insulin-like growth factor 1, or IGF-1, which is known to promote the growth of various types of cancer. Casein and whey, the predominant proteins in milk, also have been shown to cause prostate cancer cell growth, he added.
Men in the United States have an 11.6% lifetime risk for prostate cancer. Previous studies have shown that consuming high amounts of animal products can increase that risk, and prostate cancer rates in Asia — where people eat fewer dairy products — are lower than in the U.S.
Researchers also noted that declines in prostate cancer mortality rates in the U.S. have coincided with decreased consumption of meat and dairy products and increased plant-based food consumption.
Shin and colleagues sought to better understand the association between dietary patterns and risks for prostate cancer by reviewing 47 prostate cancer studies published between 2006 and 2017.
Their search of the Ovid Medline, PubMed and Embase databases yielded two very large cohort studies (100,000 or more men), six large cohort studies (at least 40,000 men), 11 medium cohort studies (at least 10,000 men), 10 small cohort studies (fewer than 10,000 men), 13 case-control studies, four meta-analyses and one population study. All of the studies investigated the association of dietary patterns or a major component of diet with prostate cancer.
Two meta-analyses, seven prospective cohort studies and one case-control study showed an association between high dairy consumption and an increased risk for prostate cancer. Six prospective cohort and seven case-control studies showed no correlation between dairy consumption and risks for prostate cancer. One prospective cohort demonstrated decreased risk with dairy consumption during childhood.
In most studies, plant-based foods appeared associated with lower or unchanged risk for prostate cancer.
Two prospective cohort studies showed an association between a vegetarian diet and decreased incidence of all cancers (RR = 0.89; 95% CI, 0.83-0.96), whereas three studies did not show this association.
Three studies showed an association of a vegan diet with decreased risk for prostate cancer (RR = 0.81; 95% CI, 0.66-0.98; HR = 0.64; 95% CI, 0.48-0.83).
Another two studies showed an association between increased vegetable intake and decreased risk for prostate cancer (RR = 0.81; 95% CI, 0.66-0.98; RR = 0.41; 95% CI, 0.22-0.74), but six studies found no difference in risk.
When assessing red meat consumption, researchers found one large population study that linked meat intake to higher prostate cancer mortality. They also identified one prospective study that showed increased incidence of advanced prostate cancer among those who ate meat 6 or 7 days a week compared with 1 day a week (HR = 1.75; 95% CI, 1.03-2.97). Two prospective studies showed no significant association between eating red meat and increased incidence of prostate cancer.
A lack of epidemiologic data, including whether patients smoked or drank alcohol, served as a limitation to the study. Additionally, some studies looked specifically at prostate cancer incidence, whereas others investigated associations between diet and aggressive prostate cancer.
“Fruits and vegetables are known to contain many phytochemicals that protect against DNA damage, reduce oxidative stress and enhance immune function, all of which are possible mechanisms for lowering cancer risk in general,” Shin told HemOnc Today. “Studies have also shown that plant-based dietary patterns as a whole, and not supplementation with isolated nutrients, seem to confer the most health benefits.” – by John DeRosier
For more information:
John Shin, MD, can be reached at Mayo Clinic, 200 First St. SW., Rochester, MN 55905; email: firstname.lastname@example.org.
Disclosures: The authors report no relevant financial disclosures.