Higher than normal amounts of vitamin B12 in the blood may indicate an increased risk of cancer.
Scientists who studied the records of more than 300,000 patients found that chances of having cancer rose with higher blood levels of vitamin B12, also known as cobalamin (Cbl).
The overall risk of cancer increased especially during the first year after having a blood test and in those patients with levels of 800 picomoles per litre (pmol/L) or more.
Researchers excluded patients who had a cancer diagnosis before the date of the blood test, and those who were receiving vitamin B therapy.
The team, led by Johan Arendt, from Aarhus University Hospital in Denmark, wrote in the Journal of the National Cancer Institute: "High plasma Cbl levels increased the risk of subsequently diagnosed cancer, mostly within the first year of follow-up."
However, the scientists pointed out that consumption of foods and supplements containing vitamin B12 do not increase blood levels of Cbl substantially. They suspected that high Cbl levels resulted from some unknown malignant process.
Vitamin B12 is essential for normal nerve functioning and the creation of red blood cells. An inability to absorb vitamin B12 can lead to pernicious anaemia.
