Brandel France de Bravo, MPH, Caitlin Kennedy, PhD, Anna E. Mazzucco, PhD, and Laura Gottschalk, PhD, Cancer Prevention & Treatment Fund
Prostate cancer is the second most common cancer among American men, and the second leading cause of cancer deaths among them as well. The American Cancer Society estimates almost 192,000 new diagnoses of prostate cancer in 2020, and more than 33,000 prostate cancer related deaths.
Compared to most cancers, prostate cancer usually progresses very slowly, and many men live with it for years and even decades. Once diagnosed, some men decide to undergo treatment to halt the progression of the disease, and others refrain from treatment, preferring instead to closely monitor the cancer’s progression. Those who choose “active surveillance” do this because the medical and surgical treatments for prostate cancer often cause very undesirable side effects, and because most men with prostate cancer will die from something else. This strategy is especially likely for older men in the earliest stage of the disease.
At one time, it was unheard of to suggest that diet might have a role to play in battling prostate cancer. But there is now evidence that certain foods and dietary supplements have an impact on prostate health—both positive and negative. Some foods or supplements appear to promote prostate health and prevent cancer cells from developing, but others should not necessarily be taken by men who already have prostate cancer.
The role of diet drew researchers’ attention when they noticed that prostate cancer rates vary greatly from one country to another, with the highest rates appearing in countries where people tend to eat a lot of fat. Studies also show that men who are obese or have a high fat diet are more likely to have prostate cancer. Diets high in saturated fats, such as the animal fats found in red meat, may pose the greatest risk. The lowest rates of prostate cancer are found in Asian countries where men eat a lot of soy foods, a rich source of naturally occurring phytoestrogens. It was hoped that by increasing men’s intake of phytoestrogens, they might reduce their risk of prostate cancer, slow its progression, or reduce the risk of prostate cancer recurring, but at least three studies have failed to find any protective benefit from phytoestrogens.
As more and more people take dietary supplements containing antioxidants, studies have been conducted to determine their effect on reducing the risk and growth of cancers, including prostate cancer. Three antioxidants that have received attention with regard to prostate health are vitamin E, selenium, and vitamin D.
Studies comparing men who live in areas of the country with high levels of selenium to men in areas with low levels suggest that this mineral protects against prostate cancer. Selenium was believed to reduce the risk of developing prostate cancer because it keeps cells from proliferating or dying off in a rapid or unusual way. An analysis in 2002 of the Nutritional Prevention of Cancer Trial revealed that the men who took selenium supplements daily were half as likely to be diagnosed with prostate cancer. However, a 2014 report based on the Selenium and Vitamin E Cancer Prevention Trial (SELECT) indicated that selenium supplements increased the risk of prostate cancer by 91% and taking vitamin E supplements increased the risk of prostate cancer by 17%. This result led the researchers to discourage men over 55 from taking amounts of vitamin E higher than the recommended dietary allowance (RDA), which is 15 mg of alpha-tocopherol. Moreover, a 2009 study found that higher selenium levels in the blood may worsen prostate cancer in many men who already have the disease. As a result of this trial, the researchers have encouraged men over 55 to limit their intake of selenium to the recommended dietary allowance (RDA) of 55 mcgs.
The SELECT findings on selenium don’t mean that antioxidants have no role to play in preventing cancer or slowing its spread. Some antioxidants may be helpful but some may encourage small cancers to grow larger. A 2014 study by researchers in the U.K. tested the effect of Pomi-T, a supplement that contains broccoli, pomegranate, green tea, and turmeric on the health of men with prostate cancer. After six months, they found that the men taking Pomi-T had a smaller increase in PSA, a protein that becomes elevated with prostate cancer, as compared to men with prostate cancer who didn’t take Pomi-T. The researchers suggest that the unique blend of polyphenols and antioxidants in the supplement had a beneficial effect on health of these prostate cancer patients.
A study published in 2016 brought yet another antioxidant, vitamin D, into the prostate cancer discussion. Vitamin D is well known for its role in helping build strong bones and teeth, but it may also contribute to the fight against cancer (read more here AND here). The prostate cancer study looked at the levels of vitamin D in men who had their prostates removed due to cancer. They found that men who had the most aggressive forms of prostate cancer had lower levels of vitamin D in their blood compared to men with less aggressive forms of cancer. It is not yet known whether higher levels of vitamin D prevent more aggressive forms of prostate cancer or if aggressive prostate cancer lowers levels of vitamin D. Since it is impossible to know if low levels of vitamin D is a cause or effect of aggressive prostate cancer, and since high levels of vitamin D can be dangerous, more research is needed before experts will know if men diagnosed with prostate cancer should try to take more vitamin D.
Bottom Line: We need studies to determine exactly how diet and dietary supplements can be used to prevent prostate cancer and slow its spread. Meanwhile, men should reduce saturated fats as much as possible. While the jury is still out on phytoestrogens, men may benefit from eating more soy products—especially if they are eating them in place of red meat!
For more on cancer and antioxidants, read here.
All articles are reviewed and approved by Dr. Diana Zuckerman and other senior staff.
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