Take vitamin B12 and B6 supplements – previously thought protect against cancer – is associated with a two- to four-fold increase in the risk of lung cancer, according to a new study. Researchers at Ohio State University found that the risk was increased only in men and was even higher in current smokers.
With 46% of adults in the UK said consuming these vitamins as part of a regular multivitamin tablet, should we be concerned?
The researchers asked more than 77,000 people how often they had taken these B vitamins, the dosage and their normal diet over the past ten years. The accuracy of recall over such a long period is questionable. Many of us would struggle to remember our diets and supplement intake over the past few days, let alone the past ten years.
To compound this problem, the food frequency questionnaire that was used for this study was actually designed for use with a different population – the Women’s Health Initiative, which studied postmenopausal women in the 1990s.
The researchers do not tell us if they have verified that this questionnaire works well with men. To do this, they could have compared the dietary information obtained by questionnaire from a sample of their population with the reference method of dietary assessment, i.e. a record of weighed foods. And, ideally, they should have checked serum vitamin levels in a sample of their population to see if they matched the reported intakes.
The formulation of supplements may also have changed over the years.
After six years, the researchers checked the participants to see if they had developed lung cancer. After controlling for many factors known to influence cancer risk, researchers reported a 30% increased risk of lung cancer associated with the use of vitamin B12 (taken as a single vitamin) and an increased 40% of the risk for those who took it. B6.
This effect was not observed for B vitamins in multivitamins or in women. For men who took high doses of individual supplements for ten years, the risk of lung cancer almost doubled and was even higher in men who smoked.
Doses thought to increase the risk of lung cancer in this study were greater than 20 mg (milligrams) per day of vitamin B6 and greater than 55 μg (micrograms) per day of vitamin B12 taken as individual supplements. These are massive doses compared to the amounts found in average multivitamin tablets (which are set according to the recommended daily allowance for adult males in the UK at around 1.4 mg for B6 and 1.5 μg for B12). In fact, the dose of B6 that was proposed to increase cancer risk in this study is close to the tolerable upper intake levels set in Europe for the maximum allowed dose in over-the-counter supplements (25 mg per day).
Association not cause
It should also be kept in mind that observational studies, such as this one, do not provide evidence of causation. There may be an entirely different factor that affects cancer risk, which just happens to be related to supplement use. Although researchers have done their best to account for known factors that influence cancer risk (such as age and history of lung disease), there may be other factors yet to be discovered.
To prove that these vitamins directly cause cancer, an experimental device such as a Randomized controlled trial would be necessary.
But while massive doses of individual B6 and B12 supplements do promote cancer, this isn’t the first time mega-doses of the vitamins have caused harm. Nutrients that may prevent cancer when consumed in food form may be harmful when taken in purified supplement form. For example, beta-carotene is the precursor form of vitamin A, which is found in fruits and vegetables.
Eating plenty of fruits and vegetables containing beta-carotene may help prevent cancer, but taking high-dose supplements has been linked to a increase in incidence of lung cancer in smokers.
The World Cancer Research Fund recommends that, to prevent cancer, we strive to meet nutritional needs through diet alone and not depend on supplements. Outraged, current dietary intakes of vitamins B6 and B12 in the UK do not give rise to concern. Most of us don’t need supplemental vitamin B6 or B12, let alone the high doses of vitamin B6 or B12 examined in this study.
It’s easy to get enough B6 from a varied and balanced diet. Good sources include chicken, fish, liver, pork, eggs, milk, soy, whole grains, peanuts and tree nuts. A high intake of vitamin B6 from food may be associated with less risk of cancer.
When vitamin B12 supplements are needed
Omnivores should have no trouble getting enough B12 from foods like meat, chicken, fish, eggs, cheese, and milk. Those of us looking to reduce our dependence on animal products, in order to reduce carbon emissions, might need consider supplementation.
There are also people with conditions such as Pernicious anemia who will need vitamin B12 supplementation, and this may take the form of injections.
Some older people and those with reduced stomach acid will also benefit from a vitamin B12 supplement. People who take vitamin B12 for these reasons, as recommended by a doctor, nutritionist, or dietitian, should continue to take their vitamin B12 supplements. They should be assured that many people with pernicious anemia have taken doses around 1000 μg daily for prolonged periodsto compensate for the impaired absorption of vitamin B12, without any apparent damage.
The bottom line for most of us is that we don’t need to take supplements of these B vitamins. Our nutrients are best obtained from food.