Columbus, OH—Despite what many average Americans may still in believe, “natural” supplements are not without risk. That was underscored again by a new study finding that long-term, high-dose supplementation with vitamins B6 and B12 is associated with a two- to four-fold increased lung cancer risk in some men.

The report in the Journal of Clinical Oncology notes that high doses are hyped by the vitamin industry as a way to increase energy and improve metabolism, but the risk actually was elevated even more in male smokers taking more than 20 mg of B6 or 55 mcg of B12 a day for 10 years—making them about four times more likely to develop lung cancer compared with nonusers.

At the same time, according to The Ohio State University Comprehensive Cancer Center–led study, male smokers using B6 at the same dosage were three times more likely to develop lung cancer.

The study is touted as the first prospective, observational study to look at the effects of long-term, high-dose B6 or B12 supplement use and lung cancer risk, point out the researchers, who also note that the supplements generally have been thought to reduce cancer risk.

To reach their determination, the study team employed data from more than 77,000 patients in the VITamins And Lifestyle (VITAL) cohort study, a long-term prospective observational study designed to evaluate vitamin and other mineral supplements in relation to cancer risk. Participants, aged between 50 and 76 years, were recruited in Washington state between the years 2000 and 2002.

Participants provided information to researchers about B-vitamin usage over the previous 10 years, including dosage. Statistical techniques were used to adjust for a range of factors including personal smoking history, age, race, education, body size, alcohol consumption, personal history of cancer or chronic lung disease, family history of lung cancer, and use of anti-inflammatory drugs.

“This sets all of these other influencing factors as equal, so we are left with a less confounded effect of long-term B6 and B12 super-supplementation,” explained lead author Theodore Brasky, PhD. “Our data shows that taking high doses of B6 and B12 over a very long period of time could contribute to lung cancer incidence rates in male smokers. This is certainly a concern worthy of further evaluation.”

Those doses are well above those received from taking a multivitamin every day for 10 years, Dr. Brasky emphasized, noting, “These are doses that can only be obtained from taking high-dose B vitamin supplements, and these supplements are many times the U.S. Recommended Dietary Allowance.”

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