Long-term, high-dose supplementation of vitamins B6 and B12 -- touted by the vitamin industry for increasing energy and improving metabolism -- may be associated with a two to four fold increased risk of lung cancer in men, new research has warned.The findings showed that male smokers who take more than 20 mg of Vitamin B6 were three times more likely to develop lung cancer, while those taking 55 micrograms of Vitamin B12 a day were approximately four times more likely to develop the disease compared to non-users."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," said Theodore Brasky from the Ohio State University These supplements have been broadly thought to reduce cancer risk, the researchers rued.Brasky said that these findings relate to doses that are well above those from taking a multivitamin every day for 10 years."These are doses that can only be obtained from taking high-dose B vitamin supplements, and these supplements are many times the US Recommended Dietary Allowance," he said, in the paper published in the Journal of Clinical Oncology.For this study, the team analysed data from more than 77,000 patients, aged between 50 and 76 who were regularly taking Vitamins B6 and B12 for a decade. The researchers adjusted for numerous 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.