Taking supplements, vitamins, or minerals can be complex when considering the risk or presence of prostate cancer. While the body needs various micronutrients, research shows that high-dose supplements of certain vitamins may increase the risk of developing prostate cancer or affect disease progression. The context, dosage, and form of the nutrient matter significantly. Before making any changes to a supplement regimen, men concerned about or diagnosed with prostate cancer must consult their oncologist or healthcare provider.
High-Dose Vitamin E and Selenium
The most significant evidence linking supplements to increased prostate cancer risk comes from the Selenium and Vitamin E Cancer Prevention Trial (SELECT). This large-scale, randomized study involved over 35,000 healthy men, testing whether supplemental selenium (200 micrograms per day) or vitamin E (400 International Units per day) could prevent prostate cancer. The findings demonstrated that neither supplement offered a protective effect.
The study was halted early, and a follow-up analysis revealed a statistically significant increase in risk for men taking only the high-dose vitamin E supplement. Men in the vitamin E-only group had a 17% increased risk of developing prostate cancer compared to those taking a placebo, equivalent to 11 additional cases per 1,000 men over seven years. This effect was dose-dependent, using an amount far exceeding the Recommended Dietary Allowance (RDA), which is typically 15 mg (about 22.4 IU) for men.
Folic Acid and Other B Vitamins
High supplemental intake of certain B vitamins, particularly folic acid (Vitamin B9) and Vitamin B12, is a concern related to prostate cancer. These nutrients are essential for DNA synthesis and repair, fundamental processes for healthy cell division. However, if cells are already abnormal or precancerous, excessive levels of these vitamins may inadvertently fuel their growth.
Studies suggest that high circulating levels of folate and Vitamin B12, often resulting from high-dose supplementation, may promote the growth or progression of existing tumors. The risk appears more pronounced for aggressive, high-grade prostate cancers, where elevated folate levels have been linked to a potentially doubled risk in some analyses. High supplemental doses may accelerate progression once the disease is established.
The Critical Distinction: Supplements Versus Food
The risks identified with vitamins like E, selenium, and folic acid are tied to their consumption in concentrated, high-dose supplement form, not from a balanced diet. The body processes isolated nutrients differently than those consumed as part of a whole food. Whole foods contain a complex matrix of fiber, antioxidants, and other micronutrients that regulate absorption and utilization in a regulated manner.
Supplements, especially high-dosage ones, bypass the body’s natural regulatory mechanisms that control how much of a nutrient is absorbed, leading to unnaturally high circulating levels. This high concentration is hypothesized to cause the adverse effects seen in large trials. A diet rich in fruits, vegetables, and whole grains ensures the intake of these nutrients in their natural, safer forms.
Supplements During Active Prostate Cancer Treatment
Men undergoing active treatment for prostate cancer, such as chemotherapy or radiation therapy, face a separate concern regarding supplements. Many conventional cancer treatments work by generating reactive oxygen species (free radicals) to damage and kill cancer cells. The concern is that taking high-dose antioxidant supplements, including high amounts of Vitamin C, Vitamin E, or beta-carotene, might counteract the effect of the therapy.
The theory suggests these high-dose antioxidants could protect cancer cells from the oxidative damage intended by the treatment, thereby reducing its efficacy. However, the evidence on this interaction remains controversial, with some studies suggesting that self-care dosages of antioxidants do not interfere with the efficacy of radiation therapy. Patients receiving treatment should disclose all supplements to their oncology team, as even seemingly benign supplements could interact with medications or treatments.