WASHINGTON, Aug. 22 (Xinhua) -- Men who took too much vitamin B6 and B12 supplements, especially those who smoke, had a significantly higher risk of developing lung cancer, a new study said Tuesday.
Vitamin B6 and B12 have long been touted by the vitamin industry for increasing energy and improving metabolism. These supplements have also been broadly thought to reduce cancer risk.
But the new study, published in the Journal of Clinical Oncology, found just the contrary if the doses are too high.
"What we found was that men who had used dietary supplements, in particular B6 and vitamin B12, at high doses for 10 years, were at significant increased risk of developing lung cancer," Theodore Brasky, who led the study at the Ohio State University Comprehensive Cancer Center, said in a statement.
"In fact, all men who used these supplements in high doses for a decade had approximately double the risk developing lung cancer, and in men who smoked, the risk was three to four times as great," Brasky said.
However, there was no increased risk of lung cancer found in women who took long-term, high-dose vitamin B6 and B12 supplements.
The findings were based on a follow-up of more than 77,000 U.S. patients for more than a decade.
The recommended daily allowance for vitamin B6 for men is only about 1.5 milligrams, and for vitamin B12, it's less than 2.5 micrograms per day.
"But if you look at these supplement bottles, they're being sold in pill form at up to 5,000 micrograms per dose, which is much, much higher than the daily recommended amount," said Brasky.
"It's very easy to get all the vitamin B you need in this country, from eating meats, chickpeas and foods like cereal that are fortified with them, so there really is no reason to supplement your vitamin B intake at these levels, and certainly not for years on end."