Taking high doses of vitamins B6 and B12 over the long term may be linked to a two- to four-fold increased risk of lung cancer in men compared to non-users, a recent study suggests.
The risk was further elevated in men who smoked and took more than 20 milligrams of B6 or 55 micrograms of B12 a day for 10 years. Men who smoked and took B6 at this high of a dose were three times more likely to develop lung cancer, while men who took B12 at such high doses were about four times more likely compared to non-users.
No such risk was identified in women.
The study was conducted by researchers at the Ohio State University Comprehensive Cancer Center, Fred Hutchinson Cancer Research Center and National Taiwan University. It is the first prospective, observational study to look at the effects of long-term high doses of these vitamin supplements and lung cancer risk.
For the study, researchers analyzed data from over 77,000 patients in the VITamins and Lifestyles (VITAL) cohort study, which is a long-term prospective observational study looking at the use of vitamin and mineral supplements and their relation to cancer risk. More than 3,200 of the men in the study were current smokers, 139 of whom already had lung cancer.
Participants were between the ages of 50 and 76 and were recruited between 2000 and 2002.
Patients were required to report information to researchers about their use of B vitamins over the previous decade, including dosage information.
They then adjusted for several factors including smoking history, age, race, education, body size, alcohol consumption, 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,” Theodore Brasky, co-author of the study, said in a statement. “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.”
It’s important to note that the doses noted are well above those from taking a multivitamin daily for 10 years, and are above the recommended dietary allowance.
The study was published Tuesday in the Journal of Clinical Oncology.
However, registered dietitian Andrea D’Ambrosio says there’s no need to panic with these results. As she points out, the study is not able to make a direct link between B vitamin intake and cancer risk.
After taking into account the 139 male smokers with lung cancer who participated in the study, D’Ambrosio says the only concrete takeaway from the study is that male smokers have a higher risk of getting lung cancer.
“The researcher I would say is a low-grade cohort study, and again we’re at no place to state that vitamin B12 or B6 causes lung cancer,” D’Ambrosio, of Dietetic Directions and spokesperson of Dietitians of Canada, said. “We can’t make that assumption because obviously there are other factors that would be at play.”
But D’Ambrosio does acknowledge that excessive intake of any vitamin supplement without the advice of a medical professional can be harmful.
For example, high doses of vitamin C when it’s not necessary can cause diarrhea, she says.
With vitamin B6 however, it’s not a vitamin that is of particular concern because many people already eat foods in their diets rich in that vitamin.
“It’s not really a vitamin of concern,’ D’Ambrosio says. “Yes, there is a toxic upper limit set for it as well, in which case yes – taking vitamins in excessive amount can be harmful for your health. I think that’s the important takeaway from this, that if you don’t need to take vitamins then we need to emphasize getting those vitamins from our dietary intake.”
With vitamin B12, she adds, supplements can be good for certain groups of people with health and medical conditions who have a difficult time absorbing B12. In these cases, a medical professional like a doctor or dietitian will prescribe the vitamins to these patients.
B12 levels are often a concern for vegetarians and vegans, D’Ambrosio points out because it’s a vitamin that is found in animal meats and animal proteins, such as chicken, beef, some fortified cereals, fish, eggs and milk. So they’ll often be advised by their doctor or dietitian to take B12 supplements.
Unlike B6, vitamin B12 has no toxic upper limit.
Foods with vitamin B6 include meat, fish, poultry, enriched cereals, nuts, lentils, vegetables and fruits.
“Educate yourself and just know that vitamins should still be taken with caution,” D’Ambrosio advises. “It should be used as a secondary measure to your diet at the advice of a medical professional.”