Vitamin B12: A Complete Beginner's Guide to What It Does, Why It Matters, and How to Get Enough

Posted July 4th 2025

Vitamin B12, a key player in maintaining overall health, often goes unnoticed until signs of deficiency emerge. It's the backbone of red blood cell formation, neurological function, DNA synthesis, and other vital processes, empowering you to take charge of your health.

Its clinical relevance spans everything from brain function and vision to pregnancy and bone health. This guide outlines the science-backed benefits of vitamin B12, who may be at risk for deficiency, and how to maintain adequate levels through diet or supplementation.

What is Vitamin B12?

Vitamin B12 (cobalamin) is a water-soluble vitamin that the body cannot produce on its own. It must be obtained through dietary sources or supplementation.

It's naturally present in animal-based foods such as meat, fish, dairy, and eggs, and it's also available in fortified plant-based products or as a supplement in oral or injectable form.

The recommended daily intake for most adults is 2.4 micrograms (mcg), although higher amounts may be advised during pregnancy or lactation.

Core Functions of Vitamin B12

Research has established that B12 is involved in:

• Red blood cell production. It enables the proper formation of red blood cells. Deficiency can lead to megaloblastic anemia, in which cells are enlarged and misshapen, impairing oxygen delivery throughout the body.
• Neurological health. B12 is critical to myelin synthesis and the maintenance of nerve function.
• DNA synthesis. It plays a direct role in cellular replication and repair.

Science-Backed Benefits of Vitamin B12

1. Red Blood Cell Formation and Anemia Prevention: Low B12 levels disrupt red blood cell formation, causing them to grow abnormally large and reduce their ability to carry oxygen. This leads to symptoms such as fatigue and weakness, which are commonly associated with megaloblastic anemia.
2. Pregnancy and Fetal Development: Adequate B12 status in early pregnancy has been associated with reduced risk of neural tube defects and other birth complications.
3. Bone Health: Individuals with lower B12 levels tend to have reduced bone mineral density, which may increase the risk of osteoporosis.
4. Vision Support: Macular degeneration, particularly age-related forms, has been associated with low intake of B-complex vitamins.
5. Mood and Mental Health: B12 may influence mental health through its role in synthesizing neurotransmitters such as serotonin. Some research reports an association between low B12 and higher rates of depressive symptoms.
6. Cognitive Function and Memory: Several studies report correlations between low-normal B12 levels and memory impairment, particularly in older adults.
7. Energy Metabolism: Although vitamin B12 is often marketed as an "energy booster," it doesn't directly provide energy. Instead, it plays a crucial role in the metabolism of fats and carbohydrates, which are the primary sources ofcellular energy. Deficiency can result in persistent fatigue due to impaired cellular energy metabolism. Supplementation helps restore normal function in individuals with deficiencies but does not enhance energy in those with adequate levels.
8. Skin, Hair, and Nail Health: B12 levels are associated with skin pigmentation, nail strength, and hair quality. Clinical cases have linked deficiency with symptoms such as hyperpigmentation, vitiligo, and stomatitis.

Who's at Risk for B12 Deficiency?

B12 deficiency can result from either insufficient dietary intake or impaired absorption of vitamin B12. At-risk populations include:

• Adults over the age of 60
• Individuals with gastrointestinal disorders such as Crohn's disease or celiac
• Those who have undergone bariatric or GI surgery
• Long-term users of proton pump inhibitors or metformin
• People following strict vegan or vegetarian diets

Symptoms may include fatigue, cognitive changes, tingling or numbness in extremities, glossitis, and pallor. If deficiency is suspected, blood testing and consultation with a healthcare provider are recommended.

How to Maintain Healthy B12 Levels

Dietary Sources Animal products remain the most reliable natural source of B12. These include:

• Shellfish such as clams and sardines
• Organ meats like liver
• Fish, including tuna and salmon
• Poultry, eggs, and dairy

For those following plant-based diets, fortified cereals, nutritional yeast, and plant-based milks with added B12 can help close the gap. It's important to ensure these fortified products are part of your regular diet to maintain adequate B12 levels.

Over-the-counter supplements are available in tablet, sublingual, spray, or gummy forms. They're generally safe and effective, especially for individuals with limited dietary intake.

Up Shot

Understanding the importance of maintaining healthy B12 levels is the first step towards a healthier you. Don't let B12 deficiency go undiagnosed. Take charge of your health and ensure you're getting enough B12 for red blood cell formation, neurological health, mood stability, and other vital functions.

If you're experiencing persistent fatigue, cognitive symptoms, or unexplained changes in skin or energy levels, a basic B12 test may offer clarity and, potentially, a simple solution.

Sources and Further Reading:

Sangle P, et al. (2020). Vitamin B12 supplementation: Preventing onset and improving prognosis of depression. 

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7688056/

Brescoli J, et al. (2015). A review of vitamin B12 in dermatology. https://pubmed.ncbi.nlm.nih.gov/25559140/

Tardy AL, et al. (2020). Vitamins and minerals for energy, fatigue and cognition: A narrative review of the biochemical and clinical evidence. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7019700/

Rogne T, et al. (2017). Maternal vitamin B12 in pregnancy and risk of preterm birth and low birth weight: A systematic review and individual participant data meta-analysis. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5390862/

Vitamin B12. (2023). https://lpi.oregonstate.edu/mic/vitamins/vitamin-B12

Ankar A, et al. (2022). Vitamin B12 deficiency. https://www.ncbi.nlm.nih.gov/books/NBK441923/

Pawlak R. (2021). Vitamin B12 status is a risk factor for bone fractures among vegans.https://pubmed.ncbi.nlm.nih.gov/34116377/

Molloy A, et al. (2014). Maternal vitamin B12 status and risk of neural tube defects in a population with high neural tube defect prevalence and no folic acid fortification. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4161975/

Nalder L, et al. (2021). Vitamin B12 and folate status in cognitively healthy older adults and associations with cognitive performance. https://pubmed.ncbi.nlm.nih.gov/33575718/

Hariz A, et al. (2023). Megaloblastic anemia. https://www.ncbi.nlm.nih.gov/books/NBK537254/

Young L, et al. (2019). A systematic review and meta-analysis of B vitamin supplementation on depressive symptoms, anxiety, and stress: Effects on healthy and ‘at-risk’ individuals. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6770181/

Oulhaj A, et al. (2016). Omega-3 fatty acid status enhances the prevention of cognitive decline by B vitamins in mild cognitive impairment. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4927899/

Merle B, et al. (2022). B Vitamins and incidence of advanced age-related macular degeneration: The Alienor Study.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9318446/

Kobe T, et al. (2016). Vitamin B-12 concentration, memory performance, and hippocampal structure in patients with mild cognitive impairment. https://pubmed.ncbi.nlm.nih.gov/26912492/

Facts about Neural Tube Defects. (2023). https://www.cdc.gov/ncbddd/birthdefects/facts-about-neural-tube-defects.html

Agron E, et al. (2022). Dietary nutrient intake and progression to late age-related macular degeneration in the age-related eye disease studies 1 and 2. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9318446/

Wahbeh F, et al. (2021). The role of Vitamin B12 and genetic risk factors in the etiology of neural tube defects: A systematic review. https://pubmed.ncbi.nlm.nih.gov/33851436/

Murkun S, et al. (2021). Effects of vitamin B12 supplementation on cognitive function, depressive symptoms, and fatigue: A systematic review, meta-analysis, and meta-regression. https://pubmed.ncbi.nlm.nih.gov/33809274/

Vitamin B12. (2023). https://ods.od.nih.gov/factsheets/VitaminB12-HealthProfessional/