A deficiency in vitamin B-12 could be a contributing factor to unexplained fatigue and a decline in muscle strength, especially in older adults, according to recent studies. Research indicates that this essential nutrient plays a critical role in supporting not only brain health but also the maintenance of healthy muscles.
Mitochondria, the powerhouses of cells responsible for converting food and oxygen into energy, may be adversely affected by low vitamin B-12 levels. A 2026 study published in the Journal of Nutrition by researchers from Cornell University and the University of Alabama at Birmingham observed that impaired mitochondrial function in skeletal muscle cells occurred in mice with mild B-12 deficiencies. These mice exhibited smaller muscles and reduced energy production.
"We see impacts on muscle mitochondrial function with what I think is a mild deficiency," said Martha Field, an associate professor at Cornell University and an author of the study. While the research is preclinical and awaits human trials, it highlights a potential link between B-12 status and muscle function.
Sarcopenia, the age-related loss of muscle strength and mass, is a common concern. A related study by Field's collaborator, Anna Thalacker-Mercer of the University of Alabama at Birmingham, found that vitamin B-12 supplementation in aging mice over 12 weeks improved mitochondrial biology and helped maintain muscle mass. "We think that the B-12 supplementation was helping to maintain muscle mass in the older mice," Thalacker-Mercer stated.
Vitamin B-12 is primarily found in animal products, making vegans and vegetarians more susceptible to deficiency. However, the ability to absorb nutrients can decrease with age, affecting individuals regardless of dietary habits. One estimate suggests that about 1 in 8 adults over 50 report low B-12 status. A sedentary lifestyle can also impact muscle health, and B-12 deficiency may exacerbate existing muscle function impairments.
Physicians may not routinely check B-12 levels, despite its importance. "At the very least, have your doctor check your B-12 levels, because a lot of doctors don’t, and it’s an easy test to run," Thalacker-Mercer advised. If a deficiency is suspected, seeking professional medical advice is crucial to determine the appropriate course of supplementation.
It is important to note that excessive intake of vitamin B-12 can also have risks. A 2020 study in JAMA Network Open linked very high concentrations of vitamin B-12 to early mortality. "I always tell people the best thing you can do is know your status," Field recommended. "Talk to your doctor, have your [B-12] status measured, and then make an informed decision whether a supplement would be appropriate."