For example, a meta-analysis of 18 randomised controlled trials (RCT) that included 74,498 individuals found that supplements containing B vitamins, including 20 to 2,000 mcg/day vitamin B12, had little or no effect on cancer incidence, cancer deaths, or all-cause mortality during follow-up periods of 2 to 7.3 years.
What health bodies say
The Mayo Clinic says: “When taken at appropriate doses, vitamin B12 supplements are generally considered safe.”
According to the NHS, adults (aged 19 to 64) need about 1.5 micrograms a day of vitamin B12.
“If you eat meat, fish or dairy foods, you should be able to get enough vitamin B12 from your diet,” says the health body.