Two micrograms is an almost unimaginable amount. It weighs less than a tiny fragment of a grain of table salt. However, adults only need about this amount of vitamin B12 every day, depending on the regimen used, to support the production of red blood cells, nerves and DNA.
In 2026, it will be 100 years since George Minot and William Murphy reported that a diet rich in liver could treat pernicious anemiathen a frequently fatal disease. His work transformed medicine and eventually led scientists to identify vitamin B12 as the substance present in the liver that treated the disease.
But the path to that breakthrough began with an unexpected clue from animal experiments. The American physician and pathologist. George Whipple had shown that liver helped the dogs recover from anemia caused by blood loss. Blood loss anemia occurs when the body loses red blood cells through bleeding. Pernicious anemia is different: the problem is not bleeding, but poor absorption of vitamin B12. Still, Whipple’s experiments pointed researchers toward the liver as a source of a powerful blood-forming factor.
Patients with pernicious anemia who had been near death often improved dramatically within weeks of consuming liver-rich diets. The success of the liver treatment eventually led scientists to isolate the deep red compound now known as vitamin B12 or cobalamin.
He is often wrong
Despite decades of research, vitamin B12 deficiency It remains common, particularly among older adults, vegans, vegetarians, and people with conditions that affect absorption. Some people do not consume enough B12 because it is found naturally primarily in animal foods, such as meat, fish, eggs, and dairy products. Others struggle to absorb it properly.
this becomes more common with age. Some older people produce less stomach acid, which is necessary to release B12 from food. Others develop autoimmune gastritisin which the immune system damages stomach cells involved in producing acid and intrinsic factorthe protein necessary for the absorption of vitamin B12. Weight loss surgery and some medications used for diabetes or acid reflux can also reduce absorption.
Deficiency symptoms can develop slowly and are often confused with normal aging. People may feel exhausted, weak, or out of breath. Some develop numbness or tingling in their hands and feet, poor balance, memory problems, or what many describe as “brain fog.” These symptoms are not specific to B12 deficiency, so persistent fatigue, tingling, or balance problems should be monitored rather than assuming it is a simple vitamin problem.
People at highest risk, including vegansVegetarians, older adults, and those taking medications that affect stomach acid or treating diabetes, may need testing or advice on supplementation from a health professional.
Doctors have traditionally linked fatigue in B12 deficiency with anemia. Without enough vitamin B12The bone marrow cannot produce healthy red blood cells. Instead, it releases unusually large, immature cells that carry oxygen less effectively around the body.
But anemia may not be the only reason why people with low B12 levels feel depleted.
Low energy
In humans, vitamin B12 is directly needed only by two enzymes, proteins that help chemical reactions occur in the body. One helps the body make DNA, which cells need when they divide. The other helps the mitochondria process certain fats and protein building blocks. Mitochondria are small structures inside cells that help convert food into usable energy.
This mitochondrial function has attracted increasing interest from researchers studying aging, muscle function and vitamin B12 status. TO study 2026 explored what happens when cells don’t have enough B12. Researchers found that a low level of B12 could interfere with the DNA within the mitochondria and reduce energy production in skeletal muscle laboratory models (muscle cells studied outside the human body).
A related study in aged female mice found that vitamin B12 supplementation improved several signs of mitochondrial impairment. muscle healthincluding the number and structure of mitochondria. Taken together, this work points to a possible reason why some people with low B12 levels report fatigue before overt anemia is detected.
These findings do not mean that vitamin B12 supplements can reverse aging or act as an energy booster for people whose B12 levels are already normal.
Scientists have suspected a relationship between B12 and mitochondrial function for many years, because one of the two B12-dependent enzymes acts within the mitochondria. Previous research has also suggested that low B12 may be linked to worse muscle function in older adultsalthough much of this work is observational and cannot prove cause and effect.
So if you constantly feel tired, is it worth paying for vitamin B12 injections at a wellness clinic or medispa? For most people, no. B12 injections are an established treatment for diagnosed deficiency, particularly when absorption is impaired and The NHS uses hydroxocobalamin injections for vitamin B12 deficiency anemia.
But there is little evidence that B12 injections increase energy, weight loss, or performance in people whose B12 levels are already normal. The most useful first step is to discover what is causing the fatigue.
The story of vitamin B12 is unusual because the body needs very little of it, and yet the consequences of its deficiency can be profound. Long before scientists understood its chemistry, doctors recognized that something in the liver could restore strength, appetite, and vitality to desperately ill patients.
A century later, researchers continue to discover that this tiny cobalt-containing molecule does more than prevent anemia. It may also help explain how cells maintain energy and function as the body ages.