By Susan E. Matthews
Vitamin B12 may be known for helping people absorb iron and maintaining the nervous system, but a new study tracking hundreds of thousands of people in Denmark found that higher levels of the vitamin were associated with higher levels of cancer. But don't throw out your supplements yet -- the researchers theorize it's more likely cancer causes high levels of B12 than B12 causing cancer.
The researchers, from Aarhus University Hospital in Denmark, made use of Danish medical registries to investigate over 330,000 patients between 1998 and 2010. These patients did not have cancer when the researchers began tracking them, but they had been referred to have their vitamin B12 levels tested. The researchers found that the patients with the highest vitamin B12 levels also had the highest risk of being diagnosed with cancer, particularly in the first year after having the vitamin measurement taken.
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"I was surprised to see such strong associations to different specific types of cancer," said study author Johan Arendt, BSc, of the department of clinical epidemiology at Aarhus University Hospital. The researchers found that risk of cancers associated with smoking and alcohol was higher, but the risk of blood-related and hormonal cancers was also elevated.
An increased vitamin B12 level makes sense for cancers associated with high intake of alcohol, such as liver cancer, the researchers noted. Cancer of the liver would inhibit the liver's functioning, and because the liver processes vitamin B12, it makes sense that the patient would have high levels of vitamin B12.
As for the correlation between B12 and other cancers, experts suggested it may be the result of the study setup.
"Think in real-time," said Mikkael Sekeres, MD, MS, director of the leukemia program at Cleveland Clinic. All of the participants the researchers tracked were having their vitamin B12 levels measured, which indicates that something was bothering them to begin with.
Sekeres theorized that a patient may come into the doctor feeling fatigued, which could lead to the doctor wanting to check vitamin levels and prescribe supplements. In reality, the cause of the fatigue could very likely be an impending cancer diagnosis, but the patient and doctor don't know this yet.
This is called "confounding by indication," Dr. Sekeres said.
Polly Niravath, MD, assistant professor at Baylor College of Medicine agreed with Sekeres' conclusion.
"You're checking B12 on these people because they have symptoms, and those symptoms make them more likely to have cancer," she said.
The resulting supplements would elevate their B12 levels prior to diagnosis. "All of this is occurring prior to the discovery of the cancer," he said.
It's also possible that something about the pathology of certain cancers results in patients having higher levels of vitamin B12 in their bloodstream, Dr. Niravath said. "Perhaps it's a reflection of something else the cancer is doing in the body," she said.
Sekeres agreed that further research is needed to determine if certain cancers elevate the level of B12 in the body, or if the results of the study were completely confounded by the study's design.
At any rate, everyone agreed that while the results are curious, they're not a reason to stop taking your multivitamins.
"It's interesting -- but not practice-changing," Niravath said.
"Study: Vitamin B12 Correlated with Higher Cancer Risk" originally appeared on Everyday Health.