Vitamin B12 May Hold Surprising Secrets About Energy and Aging in Some People

Two micrograms is an almost unimaginably small amount. It weighs less than a tiny fraction of a grain of table salt. Yet, depending on the guidelines used, adults need only about this much vitamin B12 each day to support the formation of red blood cells, nerves, and DNA. The year 2026 marks the 100th anniversary of George Minot and William Murphy’s report that a diet rich in liver could cure pernicious anemia, which was often fatal at the time. Their work revolutionized medicine and ultimately led scientists to identify vitamin B12 as the active substance in liver that cured the disease.

The Role of Vitamin B12

The path to this breakthrough, however, began with an unexpected clue from animal experiments. The American physician and pathologist George Whipple had shown that liver helped dogs recover from anemia caused by blood loss. Anemia caused by blood loss occurs when the body loses red blood cells due to bleeding. With pernicious anemia, the situation is different: the problem is not bleeding, but rather a deficiency in vitamin B12. Nevertheless, Whipple’s experiments pointed researchers toward the liver as the source of an effective blood-forming factor. Patients with pernicious anemia who were near death often showed dramatic improvement within a few weeks of switching to a diet rich in liver. The success of the liver treatment ultimately led scientists to isolate the deep-red compound now known as vitamin B12 or cobalamin.

Vitamin B12 is a vital, water-soluble vitamin belonging to the B-vitamin group. It is one of the essential nutrients that the human body cannot produce on its own and must therefore be obtained through diet. Vitamin B12 is involved in numerous metabolic processes and performs important functions in the body. It supports the formation of red blood cells, which are responsible for oxygen transport, and contributes to the normal functioning of the nervous system. It is also necessary for cell division and the formation of genetic material (DNA) and plays an important role in energy metabolism. Furthermore, this vitamin supports the normal function of the immune system and is involved in various biochemical processes necessary for growth, regeneration, and the maintenance of bodily functions. An adequate supply of vitamin B12 is therefore important to ensure that these vital processes can proceed smoothly.

Despite decades of research, vitamin B12 deficiency remains widespread, particularly among older adults, vegans, vegetarians, and people with medical conditions that impair absorption. Some people do not consume enough B12 because it occurs naturally mainly in animal-based foods such as meat, fish, eggs, and dairy products. Others have difficulty absorbing it properly. This becomes more common with age. Some older adults produce less stomach acid, which is needed to release vitamin B12 from food. Others develop autoimmune gastritis, in which the immune system damages the stomach cells involved in producing stomach acid and intrinsic factor—the protein required for the absorption of vitamin B12. Gastric bypass surgery and certain medications for diabetes or heartburn can also impair absorption.

The symptoms of a deficiency can develop slowly and are often mistaken for normal signs of aging. Those affected may feel exhausted, weak, or short of breath. Some people experience numbness or tingling in their hands and feet, balance problems, memory issues, or what many refer to as “brain fog.” Since these symptoms are not specific to a deficiency, persistent fatigue, tingling, or balance problems should be investigated rather than simply dismissed as a vitamin deficiency. People at increased risk—including vegans, vegetarians, older adults, and those taking medications that affect stomach acid or are used to treat diabetes—may need an evaluation or advice on supplementation from a healthcare professional. Doctors have traditionally linked fatigue associated with a B12 deficiency to anemia. Without sufficient vitamin B12, the bone marrow cannot produce healthy red blood cells. Instead, it releases abnormally large and immature cells that transport oxygen less effectively throughout the body. However, anemia may not be the only reason why people with low B12 levels feel exhausted.

Vitamin B12 and Mitochondrial Function

In humans, vitamin B12 is directly required by only two enzymes—the proteins that enable chemical reactions in the body. One helps the body produce the DNA that cells need for cell division. The other supports the mitochondria in processing certain fats and protein building blocks. Mitochondria are the tiny structures inside cells that help convert food into usable energy.

This role of mitochondria is attracting growing interest among researchers studying aging, muscle function, and vitamin B12 status. A 2026 study investigated what happens when cells do not have enough B12. The researchers found that low B12 levels could impair the DNA in the mitochondria and reduce energy production in laboratory models of skeletal muscle (muscle cells studied outside the human body).

A related study in older female mice found that vitamin B12 supplementation improved several markers of mitochondrial health in muscle, including the number and structure of mitochondria. Taken together, these studies suggest a possible reason why some people with low vitamin B12 levels complain of fatigue before obvious anemia is diagnosed. However, these findings do not mean that vitamin B12 supplements can reverse the aging process or serve as an energy boost for people whose vitamin B12 levels are already normal.

Scientists have long suspected a link between vitamin B12 and mitochondrial function, as one of the two B12-dependent enzymes acts within the mitochondria. Previous research also suggests that low vitamin B12 levels may be associated with poorer muscle function in older adults, although the majority of these studies are observational and cannot prove a causal relationship.

How Cells Maintain Their Energy and Function as the Body Ages

So if you’re feeling persistently tired: Is it worth paying for vitamin B12 injections at a wellness clinic or medspa? For most people: no. B12 injections are an established treatment for diagnosed deficiency, especially when absorption is impaired, and the NHS uses hydroxocobalamin injections to treat vitamin B12-deficient anemia.

However, there is little evidence that B12 injections boost energy, promote weight loss, or improve performance in people whose B12 levels are already normal. The more sensible first step is to find out what is causing the fatigue. The history of vitamin B12 is unusual because the body needs only a very small amount of it, yet the consequences of a deficiency can be severe. Long before scientists understood its chemical properties, doctors recognized that a certain substance in the liver could restore strength, appetite, and vitality in critically ill patients. A century later, researchers are still discovering that this tiny, cobalt-containing molecule can do more than just prevent anemia. It may also help explain how cells maintain their energy and function as the body ages.