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What You Need To Know About Vitamin B12

A bottle of B12 supplement tablets.
Credit: Cristi Ursea/ Unsplash
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What is vitamin B12 and why is it important?

Naturally found in foods of animal origin including meat, fish, eggs and dairy, vitamin B12 is essential for the development and function of the central nervous system, red blood cell formation and DNA synthesis. Some breakfast cereals and nutritional yeasts are supplemented with vitamin B12, providing an alternative source for vegans.

The recommended dietary allowance of B12 for non-breastfeeding adults is 2.4 µg per day, which is approximately the amount found in 85 g of cooked ground beef. For pregnant people and those breastfeeding, this figure increases to 2.6 µg per day and 2.8 µg per day, respectively.

What are the symptoms of vitamin B12 deficiency, and what’s the latest research?

The British Medical Journal reported that vitamin B12 deficiency is a “common but serious condition” that may not have an obvious clinical presentation, thus “leading to complex issues around diagnosis and treatment.”

Approximately 6% of adults under 60 have a vitamin B12 deficiency. As humans age and our metabolism changes, this figure increases to 20% in those over 60.

Symptoms of vitamin B12 are varied and can include cognitive impairment, mental health problems, indigestion, vision changes and palpitations.

Researchers are actively studying the role of vitamin B12 in the human body, as well as the consequences when levels are low.

Low vitamin B12 linked to inflammation

A recent study, published in the Journal of the Science of Food and Agriculture, illustrated a link between vitamin B12 and two molecules that promote inflammation interleukin (IL)-6 and C-reactive protein (CRP).1

The researchers analyzed data from 136 participants of the PREDIMED trial, which was originally designed to assess the effect of a Mediterranean diet on the risk of cardiovascular disease.

The more vitamin B12 present in an individual’s blood sample, the lower the concentrations of IL6 and CRP, which are key markers of inflammation in clinical practice, the researchers found. 

“It will be interesting to understand if vitamin B12 supplementation can play a role in disease management,” said Rosa M. Lamuela-Raventós, co-corresponding author of the study and professor of nutrition, food sciences and gastronomy at the University of Barcelona.

While the team did not study individuals with vitamin B12 deficiency specifically, the study’s co-first author, Dr. Marta Kovatcheva explained that this study identifies a new relationship: “This might help us better understand why some unexplained symptoms of human B12 deficiency, like neurologic defects, occur.”

The participants of the PREDIMED trial represent a small subsection of the population, and the authors emphasize that exploring sex-specific differences will be critical in future research.

Micronutrient deficiencies associated with rise in antibiotic resistance

A recent study from The University of British Columbia (UBC) reported a “surprising” link between micronutrient deficiencies, the gut microbiome and antibiotic resistance.2 Deficiencies in crucial micronutrients – including vitamin B12 – can influence the gut microbiome in mice, leading to the expansion of opportunistic pathogens.

They also discovered that mice with micronutrient deficiencies possessed microbiomes with a greater prevalence of genes that are linked to antibiotic resistance. “This is a significant discovery, as it suggests that nutrient deficiencies can make the gut environment more conducive to the development of antibiotic resistance, which is a major global health concern,” Dr. Paula Littlejohn, a postdoctoral research fellow with UBC’s department of medical genetics and department of pediatrics, and lead author of the study, said.

What are the new NICE guidelines on B12 deficiency?

The National Institute for Health and Care Excellence (NICE) recently published the first-ever guidelines for vitamin B12 deficiency diagnosis and management, aiming to raise awareness of the condition and improve diagnosis and ongoing care.

The new NICE guidelines outline the serum concentrations of total and active vitamin B12 that constitute a deficiency diagnosis, as well as the serum concentrations that require follow-up.

Total B12 concentrations must be less than 180 ng/L or active B12 is less than 25 pmol/L (if not pregnant or breastfeeding) for a deficiency diagnosis. Indeterminate results that require follow-up are total B12 concentrations between 180 and 350 ng/L, according to the guidelines.

A blood test for vitamin B12 deficiency is recommended if a patient has one symptom and one or more risk factors – which include age, autoimmune conditions and previous surgery of the digestive system.

The release of these guidelines has raised questions among healthcare professionals and patients.

The new guidelines recommend that “treatment should be considered if [the patient’s] test is indeterminate and vitamin B12 deficiency is suspected”,  to which Dr. Rehaan Anssri, a GP partner at Cliff House Medical Practice, said, “We risk veering into the realms of ‘wellness’ rather than ‘health’ if we start offering injectable B12 supplementation to all with a B12 less than 300 who are feeling fatigued or have brain fog.”

Vitamin B12, alongside other micronutrients, is increasingly being offered by “wellness” or beauty clinics as part of a wellbeing “menu”, promising benefits such as increased energy, easier weight loss, a healthier cardiovascular system and even curing a hangover. However, a study by Dr. Kathryn Kolasa and Sahil Dayal “did not find evidence-based guidelines for uses such as these for intravenous vitamin therapies outside conventional medical settings.”3

Anssri also opined that the guidelines omit that a patient’s vitamin B12 deficiency symptoms should be analyzed to rule out any other underlying causes, such as perimenopause, chronic fatigue syndrome or other nutrient deficiencies.

More awareness needed

A patient’s response to the guidelines emphasized that vitamin deficiency does not form a part of first-line testing by GPs, and supplementation is not yet widely recognized as a viable therapeutic option.  “More clarity is needed,” added Dr. Ian Beales, a clinical associate professor at the University of East Anglia, “on the optimal diagnosis and management of vitamin B12 deficiency.”

Charities and organizations such as the vitamin B12 deficiency charity support group and CLUB-12 aim to raise awareness of vitamin B12 deficiency and the uncertainties surrounding diagnosis and treatment, while also promoting further research.


1. Domínguez-López I, Kovatcheva M, Casas R, et al. Higher circulating vitamin B12 is associated with lower levels of inflammatory markers in individuals at high cardiovascular risk and in naturally aged mice. J Sci Food Agricult. 2023. doi: 10.1002/jsfa.12976

2. Littlejohn PT, Metcalfe-Roach A, Cardenas Poire E, et al. Multiple micronutrient deficiencies in early life cause multi-kingdom alterations in the gut microbiome and intrinsic antibiotic resistance genes in mice. Nat Microbiol. 2023. doi: 10.1038/s41564-023-01519-3

3. Dayal S, Kolasa K. Consumer intravenous vitamin therapy: Wellness boost or toxicity threat? Nutrition Today. 2021; 56:234-238. doi: 10.1097/NT.0000000000000500