Two micrograms is an almost unimaginably small amount. It weighs less than a tiny fragment of a grain of table salt. Yet adults need only around this amount of vitamin B12 each day, depending on the guideline used, to support red blood cells, nerves and DNA production.

In 2026, it is 100 years since George Minot and William Murphy reported that a liver-rich diet could treat pernicious anaemia, then a frequently fatal disease. Their work transformed medicine and eventually led scientists to identify vitamin B12 as the substance in liver that treated the disease.

But the route to that breakthrough began with an unexpected clue from animal experiments. The American physician and pathologist George Whipple had shown that liver helped dogs recover from anaemia caused by blood loss. Blood-loss anaemia happens when the body loses red blood cells through bleeding. Pernicious anaemia is different: the problem is not bleeding, but poor absorption of vitamin B12. Even so, Whipple’s experiments pointed researchers towards liver as a source of a powerful blood-forming factor.

Patients with pernicious anaemia who had been close to death often improved dramatically within weeks of eating liver-rich diets. The success of liver treatment eventually led scientists to isolate the deep red compound now known as vitamin B12, or cobalamin.

Despite decades of research, vitamin B12 deficiency remains common, particularly among older adults, vegans,........

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