Vitamin B12 Deficiency Risks and Effects on Older Adults

Adults require approximately two micrograms of vitamin B12 daily to support essential functions such as red blood cell formation, nerve health, and DNA synthesis. This quantity is extraordinarily small, weighing less than a fragment of table salt.

In 2026, the centenary of George Minot and William Murphy’s discovery approaches; they demonstrated that a diet rich in liver could treat pernicious anemia, a disease once often fatal. This breakthrough eventually led to identifying vitamin B12 as the active component in liver responsible for the treatment.

The initial clue came from George Whipple’s animal studies, where liver helped dogs recover from anemia caused by blood loss. While pernicious anemia results from poor vitamin B12 absorption rather than bleeding, Whipple’s findings directed researchers toward liver as a source of a vital blood-forming factor.

Patients with pernicious anemia, near death before treatment, often showed dramatic improvement within weeks of consuming liver-rich diets. This success spurred the isolation of vitamin B12, also known as cobalamin, the deep red compound responsible for the therapeutic effect.

Prevalence and Causes of Vitamin B12 Deficiency

Despite extensive research, vitamin B12 deficiency continues to affect many, especially older adults, vegans, vegetarians, and individuals with absorption issues. The vitamin is primarily found in animal-derived foods such as meat, fish, eggs, and dairy, leading to inadequate intake in some diets.

Absorption difficulties increase with age due to factors like reduced stomach acid production, which is necessary to release vitamin B12 from food. Autoimmune gastritis, damaging stomach cells that produce acid and intrinsic factor (a protein essential for B12 absorption), also contributes. Additionally, weight-loss surgeries and medications for diabetes or acid reflux can impair absorption.

Symptoms often develop gradually and may be mistaken for normal aging. These include fatigue, weakness, shortness of breath, numbness or tingling in extremities, balance problems, memory issues, and cognitive disturbances commonly described as “brain fog.” Since these symptoms are not exclusive to B12 deficiency, persistent signs warrant medical evaluation rather than assumptions of a simple vitamin shortfall.

Individuals at elevated risk, including older adults, vegans, vegetarians, and those on certain medications, may require professional testing or guidance on supplementation.

How Vitamin B12 Deficiency Affects Energy and Blood Cells

Tiredness associated with vitamin B12 deficiency has traditionally been linked to anemia. Without sufficient B12, the bone marrow produces abnormally large and immature red blood cells that are less effective at transporting oxygen throughout the body.

However, anemia might not fully explain fatigue in B12 deficiency. Vitamin B12 is essential for two enzymes: one involved in DNA synthesis needed for cell division, and another functioning within mitochondria to process specific fats and protein components. Mitochondria are cellular structures responsible for converting food into usable energy.

Vitamin B12’s Role in Mitochondrial Function

Research into vitamin B12’s mitochondrial role has increased, particularly regarding aging and muscle function. A 2026 study found that insufficient B12 impairs mitochondrial DNA and reduces energy production in skeletal muscle cells studied in laboratory settings.

Another study involving aged female mice showed that B12 supplementation improved mitochondrial health indicators in muscle tissue, including mitochondrial number and structure. These findings suggest a potential explanation for fatigue reported by some individuals with low B12 before anemia becomes apparent.

These results do not imply that vitamin B12 supplements can reverse aging or enhance energy in individuals with normal B12 levels.

Scientists have long suspected a connection between B12 and mitochondrial function due to one of the B12-dependent enzymes operating inside mitochondria. Earlier observational studies have also linked low B12 status with reduced muscle function in older adults, though causality remains unproven.

Evaluating Vitamin B12 Injections for Fatigue

Vitamin B12 injections are an established treatment for diagnosed deficiency, especially when absorption is impaired. The NHS uses hydroxocobalamin injections to treat vitamin B12 deficiency anemia.

However, there is limited evidence supporting the use of B12 injections to boost energy, promote weight loss, or improve performance in individuals with adequate B12 levels. The recommended initial step for persistent tiredness is to identify its underlying cause rather than seeking injections without medical indication.

The history of vitamin B12 is notable for the body’s minimal requirement contrasted with the significant effects of deficiency. Before its chemical nature was understood, physicians recognized that liver consumption could restore strength and vitality to severely ill patients.

One hundred years later, ongoing research continues to reveal that this small cobalt-containing molecule contributes to more than anemia prevention, potentially playing a role in cellular energy maintenance and function during aging.