Previous studies had suggested an association between high Cbl levels and specific cancers.
To assess the association between high Cbl levels and risk of cancer of any type, Johan Arendt, BSc, of the Department of Clinical Epidemiology and the Department of Clinical Biochemistry of Aarhus University Hospital in Denmark, and colleagues used Danish Medical registries to review the records of 333,667 patients without cancer who had been referred for Cbl testing and to estimate the incidence of cancer in this population from 1998 to 2010.
The researchers excluded patients who had a cancer diagnosis before the date of plasma measurement and those who were receiving Cbl therapy. They found that the risk of cancer overall increased with higher Cbl levels, especially during the first year after measurement and for those with levels > 800pmol/L. They also found that after five years of follow-up, the risk for hematological and alcohol and smoking-related cancers remained high for those with levels > 800pmol/L.
The authors conclude that "...high plasma Cbl levels increased the risk of subsequently diagnosed cancer, mostly within the first year of follow-up." However, Arendt et al. note that high plasma Cbl levels are probably not related to normal Vitamin B12 intake because consumption of Cbl containing foods or supplements do not increase plasma Cbl levels substantially. Rather, high Cbl levels may result from some unknown malignant process.