Smokers Who Take This Vitamin Could Be at Higher Risk for Cancer

Updated: Aug. 11, 2022

Nutritional supplements and vitamins have been all the rage, but—especially for some—there are important cautions that doctors and scientists think you should know.

If-You-Take-These-Supplements,-You-Could-Be-at-Risk-of-Cancer-450435058-MK-photograp55MK photograp55/shutterstockThere are lots of reasons to make sure you get enough of the eight B vitamins, all of which are said to increase energy, and two of which—B6 and B12—are said to support production of serotonin, which is crucial to avoiding and overcoming depression. (These are the signs of vitamin B deficiency.) Since around 2010, some people have believed that taking vitamin B6 supplements may help prevent lung cancer. However, an important heads-up has emerged from recent years of research: a 2017 study published in the Journal of Clinical Oncology found that taking high doses of Vitamin B6 and Vitamin B12 was associated with an increased risk of lung cancer in men, particularly in smokers.

The study was led by Theodore Brasky, PhD—an epidemiologist with The Ohio State University Comprehensive Cancer Center-Arthur G. James Cancer Hospital and Richard J. Solove Research Institute (OSUCC-James)—and used data from more than 77,181 men and women, ages 50 to 76. The data were employed to evaluate vitamin supplementation in relation to cancer risk. For the long-term study, the participants reported their use of vitamin supplements over the preceding 10 years, among other things. Using a cancer registry, Dr. Brasky’s team determined that 808 of the participants went on to develop lung cancer in the years that followed.

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Crunching the numbers, including precise Vitamin B dosages the participants reported having taken, the researchers found that the use of vitamin B6 and B12 from individual supplement sources—but not from multivitamins—was associated with a 30 to 40 percent increase in lung cancer risk among the men. In fact, the men who took the highest dosage of these vitamins over a 10-year period were found to be twice as likely to develop lung cancer. Among male smokers, the risk was even higher:

  • Male smokers who took more than 20 milligrams (mg) of Vitamin B6 per day were found to be three times more likely to develop lung cancer
  • Male smokers who took more than 55 micrograms of B12 were four times more likely to develop lung cancer

These doses are well beyond what the Mayo Clinic says are the U.S. Recommended Daily Allowances of 2.4 micrograms for vitamin B-12 and between 1.3 to 1.7 micrograms of vitamin B-6. (The exact B-6 dose is determined by an individual’s age and gender.) In addition, the connection between Vitamin B supplementation and lung cancer wasn’t found among women in this particular study..

Regarding prior research suggesting that Vitamin B6 helped prevent lung cancer, Dr. Brasky clarified for Reader’s Digest that the results of that particular study were based not on self-reported vitamin use, but on blood levels of B6, which may be indicative of nothing more than how much Vitamin B6 is in a person’s blood on the day the levels were measured. In other words, elevated levels of B6 in a person’s blood on any given day may not be related to how much B6 they are taking overall, and over the long term.

In addition, the prior research only evaluated Vitamin B6 usage. It therefore did not even suggest that Vitamin B12 could help prevent lung cancer.

Whether the connection holds up for B6, the takeaway should be more about not smoking than not taking supplements, according to Dr. Brasky. “Smoking causes lung cancer,” he points out, “and Vitamin B may be fueling an already existing but as-yet-undiagnosed disease process.” In any event, unless you have a significant risk for a B12 deficiency, there may be no reason to take high doses of supplements. Do your best to get your vitamins and minerals from a healthy diet, and speak with your licensed healthcare provider before adding a regular supplement to your routine.

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