Widespread vitamin B12 deficiency and associated diseases require immediate action

Around three billion people worldwide are now deficient in vitamin B12, primarily due to plant-based dietary patterns, medication use, and aging processes. Vitamin B12 deficiency can lead to anemia, fatigue, impaired concentration, infections, gastrointestinal disorders, cardiovascular disease, reduced fertility, nerve damage, and dementia, among other conditions. Because it can take several months for a deficiency to manifest after dietary changes toward plant-based eating - and because neurological symptoms may occur without the presence of anemia - many people fail to recognize the connection. There is also evidence that vitamin B12 deficiency is associated with a higher risk of hospitalization, complications, and premature death, which calls for immediate action by health authorities. This was shown in a large Brazilian population study published in Frontiers in Nutrition.

Vitamin B12 deficiency (cobalamin deficiency) has become an increasingly widespread global problem. The deficiency has long been prevalent in low-income countries due to poverty and limited access to animal foods such as meat, fish, shellfish, eggs, and dairy products. In addition, many people in Western countries have shifted toward plant-based diets due to various trends and campaigns. A growing elderly population, increased medication use, and the prevalence of chronic diseases now contribute to the fact that an estimated 39 percent of the global population is deficient in vitamin B12.
The widespread deficiency has major consequences for public health. The purpose of the Brazilian population study was therefore to investigate whether vitamin B12 deficiency is associated with related diseases and hospital admissions. The researchers used data from public and private healthcare systems covering the period from 2016 to 2023. These data were also used to assess participants’ vitamin B12 status based on blood tests and hospital admissions over time.
In total, the researchers analyzed 84 million blood tests and found that the risk of hospitalization increased by 32 percent during the study period among individuals with vitamin B12 deficiency. The deficiency was particularly associated with hospital admissions due to cardiovascular disease, blood disorders, gastrointestinal diseases, as well as neurological and psychiatric conditions. In addition, vitamin B12 deficiency frequently occurred together with deficiencies of other B vitamins such as vitamin B1 and vitamin B6, resulting in a harmful combined effect.
According to the researchers, the rising prevalence of vitamin B12 deficiency represents a serious and overlooked global health problem that requires immediate action by health authorities, both in prevention efforts and as part of the treatment of many symptoms and diseases.

Absorption and vital functions of vitamin B12 in the body

Vitamin B12 (cobalamin) is obtained exclusively from animal foods, and its absorption from the small intestine into the bloodstream requires the carrier protein intrinsic factor, which is produced in the lining of the stomach. After absorption from foods and most supplements, vitamin B12 is converted into methylcobalamin, which circulates in the blood, and into 5′-deoxyadenosylcobalamin, which is stored in the liver.
The body uses vitamin B12 for the following functions:

• Production of red blood cells
• Energy metabolism
• DNA synthesis
• Synthesis of myelin, which protects nerve cells
• Nervous system function and cognitive abilities
• Immune function
• Conversion of homocysteine in cooperation with folate and vitamin B6
• Growth in children

As part of the introduction to the new study, the authors describe how vitamin B12 deficiency can increase the risk of the following conditions:

• Pernicious anemia due to lack of intrinsic factor
• Megaloblastic anemia
• Neurological dysfunction
• Cognitive decline and dementia
• Neuropathy, including diabetic neuropathy
• Mood disturbances
• Depression and psychotic disorders
• Cardiovascular disease related to elevated homocysteine levels
• Reduced bone mineral density
• Increased risk of osteoporosis, particularly in older adults
• Gastrointestinal diseases such as Crohn’s disease and celiac disease

Causes of deficiency and impaired utilization

As mentioned, the growing trend toward plant-based diets has contributed significantly to the increased prevalence of vitamin B12 deficiency worldwide. However, because the body can store vitamin B12 in the liver, it may take several months or more than a year for a deficiency to develop after switching to a plant-based diet.
Aging processes and alcohol misuse are known to impair the body’s ability to methylate and utilize vitamin B12. Acid-suppressing medications, the arthritis drug methotrexate, and the diabetes medication metformin also reduce the absorption or utilization of vitamin B12. The same applies to certain chronic gastrointestinal disorders such as Crohn’s disease and celiac disease, as well as long COVID-19 syndrome.

Necessary treatment with supplements or injections

If vitamin B12 deficiency is caused by a plant-based diet, it can usually be treated easily through dietary changes or supplementation.
A vitamin B12 supplement should contain at least 2.5 micrograms, which corresponds to the daily reference intake. Because many individuals have difficulty absorbing and utilizing the vitamin, some supplements contain much higher doses. Vitamin B12 supplements are also available as lozenges containing the methylated form methylcobalamin, which generally provides higher absorption through the oral mucosa and improved utilization.
Severe deficiencies can be treated quickly with vitamin B12 injections. In cases of pernicious anemia, treatment should be repeated every 2-3 months due to the lack of intrinsic factor.

References:

Leonardo P. de Carvalho et al. Vitamin B12 deficiency and its impact on healthcare: a population-level analysis and call for action. Frontiers in Nutrition. 05 January 2026

Sakshi S Jajoo et al. Etiology, Clinical Manifestations, Diagnosis, and Treatment of Cobalamin (Vitamin B12) Deficiency. Cureus 2024

Simone Passarelli et al. Global estimation of dietary micronutrient inadequacies: a modeling analysis. The Lancet Global Health 2024