Vitamin B12 deficiency risks rise with age, researchers warn

Adults need only a tiny daily amount of vitamin B12, but researchers say the consequences of not getting or absorbing enough can be serious, especially with age. The nutrient supports red blood cell production, nerve function and DNA formation, and newer research is examining its role in how muscle cells make energy.

Martin Warren, writing in The Conversation, said many guidelines put adult daily needs at about 2 micrograms. Vitamin B12, also called cobalamin, is found mainly in animal-derived foods such as meat, fish, eggs and dairy products, which puts vegans and some vegetarians at higher risk of low intake.

Deficiency can also stem from poor absorption. According to Warren, older adults are more likely to produce less stomach acid, which helps free B12 from food. Autoimmune gastritis can damage stomach cells involved in producing acid and intrinsic factor, a protein needed for B12 absorption.

Weight-loss surgery and some drugs used for diabetes or acid reflux can also reduce absorption, Warren wrote. The NHS lists vitamin B12 or folate deficiency anemia as a condition that can cause tiredness, weakness and other symptoms, and says treatment depends on the cause.

Symptoms can be confused with aging

Low B12 can develop gradually, which can make it hard to spot. Warren said symptoms may include fatigue, weakness, shortness of breath, tingling or numbness in the hands and feet, balance problems, memory issues and a sense often described as brain fog.

Those problems are not specific to B12 deficiency. Warren advised that persistent tiredness, tingling or balance changes should be assessed rather than assumed to be a routine vitamin issue or a normal part of aging.

Doctors have long connected B12 deficiency with anemia. Without enough B12, bone marrow cannot make healthy red blood cells; instead, it releases unusually large immature cells that carry oxygen less efficiently, according to Warren.

The history of that treatment reaches back a century. In 1926, George Minot and William Murphy reported that a liver-rich diet could treat pernicious anemia, then often fatal. Their work followed experiments by George Whipple showing that liver helped dogs recover from anemia caused by blood loss, and it later helped lead scientists to identify vitamin B12 as the active compound in liver.

Energy research focuses on mitochondria

Warren said researchers are now paying closer attention to B12’s role inside mitochondria, the cell structures that help convert food into usable energy. In humans, B12 is directly required by two enzymes: one involved in DNA production and one involved in mitochondrial processing of certain fats and protein building blocks.

A 2026 study cited by Warren found that low B12 disrupted mitochondrial DNA and reduced energy production in laboratory models of skeletal muscle. A related study in aged female mice found that B12 supplementation improved several measures of mitochondrial health in muscle, including mitochondrial number and structure.

Those findings may help explain why some people with low B12 report fatigue before clear anemia appears, Warren said. Earlier research has also linked low B12 status with poorer muscle function in older adults, though much of that evidence is observational and does not prove cause and effect.

Researchers are not saying B12 supplements slow aging or boost energy in people whose levels are normal. Warren said injections are an established treatment for diagnosed deficiency, particularly when absorption is impaired, and the NHS uses hydroxocobalamin injections for vitamin B12 deficiency anemia.

For most people seeking energy or weight-loss benefits, Warren said there is little evidence that B12 shots help if B12 levels are already normal. He said the better first step for ongoing fatigue is to identify the cause and seek testing or supplementation advice when risk factors are present.

This story draws on original reporting from Medical Xpress.