Several studies have indicated a link between vitamin B12 and prostate cancer. That doesn’t mean you should avoid this essential nutrient; in fact, it is critical for nervous system and red blood cell health, as well as converting carbohydrates into glucose, which in turn fuels the body. Vitamin B12 also is assists in maintaining a healthy digestive system, protects against heart problems by keeping unhealthy cholesterol levels in check, promoting healthy skin and hair, and protecting against prostate, breast, colon, and lung cancers.
However, men are encouraged to avoid excessive intake of vitamin B12, as numerous research endeavors indicate that elevated levels of the vitamin may increase the risk of prostate cancer. One study noted a threefold increased risk of developing prostate cancer when vitamin B12 was elevated in the blood. (Hultdin 2005)
In the European Prospective Investigation into Cancer and Nutrition Study, researchers found that high levels of vitamin B12 could be linked to an increased risk of developing advanced prostate cancer. (Johansson 2008) A later study (2017) that included data from six cohort studies (6,875 cases and 8,104 controls) and an average follow-up of 8.9 years also found that higher concentrations of vitamin B12 were associated with a small increase in the risk of prostate cancer.
It is recommended that men follow the RDA for vitamin B12, which is 2.4 micrograms daily.
Hultdin J et al. Plasma folate, vitamin B12, and homocysteine and prostate cancer risk: a prospective study. International Journal of Cancer 2005; 113(5): 819-24.
Johansson M et al. Circulating concentrations of folate and vitamin B12 in relation to prostate cancer risk: results from the European prospective Investigation into Cancer and Nutrition study. Cancer Epidemiol Biomarkers Prev 2008; 17(2): 279-85.
Price AJ et al. Circulating folate and vitamin B12 and risk of prostate cancer: a collaborative analysis of individual participant data from six cohorts including 6875 cases and 8104 controls. European Urology 2016 Dec; 70(6): 941-51