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Excess vitamin B12 is a topic often surrounded by confusion and myths. While this vitamin is essential for proper bodily function, particularly for red blood cell production and maintaining neurological health, concerns sometimes arise regarding its effects in cases of overconsumption.
Some fear that high levels of B12 could lead to health problems, ranging from acne to increased risks of certain diseases.
Misconceptions about excess B12
Before diving into the core subject, let's begin by dispelling some common misconceptions:
❓ "Excess B12 can cause acne"
According to a small case study, very high doses of oral B12 (12 mg!) were able to trigger symptoms such as acne in a young woman (Banavath et al., 2019). But these massive doses are extremely rare and reserved for very specific cases. At usual nutritional doses, no risk of acne has been reported.
❓ "Too much B12 can excessively boost energy"
Unfortunately, no! Even at high doses, B12 does not provide "superpowers" (Guzman-Venegas et al., 2022). It merely corrects deficiencies and ensures good energy metabolism. No energy overdose in sight!
❓ "Excess B12 promotes cancer"
This fear is understandable, but the evidence is very limited. A 2015 meta-analysis even suggested that B12 supplementation could reduce the risk of colorectal cancer, especially at high doses (Das et al., 2015). But further studies are still needed.
As you can see, B12 is not the wicked witch it's sometimes described as! But what then are the real risks of an excess? That's what we'll look at now.
When should one be wary of excess B12?
No need to panic; a simple, temporary excess of B12 from food poses no danger. This vitamin is water-soluble, so surpluses are simply eliminated in the urine.
However, persistently high levels in the blood can sometimes indicate an underlying health problem. This was shown in a 2023 meta-analysis of 22 studies and over 92,000 participants (Liu et al., 2023):
🔴 A serum vitamin B12 level above 600 pmol/L (approximately 800 ng/L) was associated with a 50% increase in the risk of all-cause mortality.
🔴 A level between 400 and 600 pmol/L was also linked to a 34% increase in mortality risk.
These figures may seem alarming, but they do not mean that B12 itself is dangerous. Rather, they indicate that chronic excess B12 in the blood can be a sign of a pathology such as:
- Liver dysfunction
- Chronic kidney failure
- Certain cancers (especially hematological)
- Autoimmune or inflammatory diseases
So, in case of persistently high levels, it is better to consult a doctor to find the cause rather than to panic. B12 is only the messenger, not the problem itself! In addition, correlation does not necessarily mean causation, so these results should be taken with a grain of salt pending more in-depth studies.
At what doses does B12 remain safe?
Fortunately, usual nutritional intakes of B12 are well below risk thresholds. According to health authorities, daily requirements are (ANSES, 2016):
- 2.4 μg/day for adults
- 2.6 μg/day for pregnant women
- 2.8 μg/day for breastfeeding women
These small doses, easily covered by a balanced diet rich in animal products (meats, eggs, dairy products) or fortified foods, help maintain adequate body stores of B12.
Even with supplementation, you would really have to force the dose to reach worrying levels. Most supplements do not exceed 1000 μg per dose, which is 400 times the requirements! And a recent meta-analysis reported no worrying side effects up to doses of 2000 μg per day (Mikkelsen et al., 2021).
So, except in very specific cases (medical treatments, specific diseases), it is almost impossible to reach dangerous B12 levels through simple oral supplementation at standard doses.
As you can see, a temporary and moderate excess of B12 is not to be feared. But what about the potential benefits of B12 supplementation?
B12 supplementation: for whom and in what cases?
As with any supplementation, the benefits of B12 intake largely depend on the initial situation. Simply put, it's all about balance!
For deficient individuals
If your B12 reserves are low, for example due to a too restrictive diet or absorption problems, supplementation can be an excellent option to:
✅ Prevent anemia
✅ Combat fatigue
✅ Preserve neurological and cognitive functions. A 2021 meta-analysis also showed that B12 supplementation could improve depressive symptoms and stress in deficient or at-risk individuals (Gouffe et al., 2021).
For older adults
With age, B12 absorption becomes less efficient due to a decrease in hydrochloric acid and intrinsic factor production in the stomach. Moderate supplementation (a few hundred μg per day) may then be recommended from age 50 to prevent deficiencies (Langan et al., 2017).
For vegans and strict vegetarians
Since animal products are the main sources of B12, diets of total exclusion expose individuals to a high risk of deficiency. B12 supplementation is essential for these individuals, typically at doses of 25 to 100 μg per day (Bärebring et al., 2022).
For the rest of the population
If you do not belong to any of these at-risk groups and your diet is balanced, there is no need to worry about B12 supplementation. Unless medically advised otherwise, your dietary intake is amply sufficient to cover your needs! As you can see, B12 is a precious friend that should not be taken in too much or too little. The key is to find the right balance, according to your lifestyle and health status.
Scientific references
Anses (2016). Actualisation des repères du PNNS : révision des repères de consommations alimentaires. https://www.anses.fr/fr/system/files/NUT2012SA0103Ra.pdf
Banavath, S., Kumari, S., & Sharma, R. (2019). Toxicity induced by multiple high doses of vitamin B12 during treatment of severe pernicious anemia. Journal of Pharmacology & Pharmacotherapeutics, 10(2), 101–103. (https://doi.org/10.4103/jpp.JPP_197_18)
Guzmán-Venegas, R., Román, S., & Michea, L. (2022). The Myths and Truths of Vitamin B12. WebMD. (https://www.webmd.com/diet/features/b12-truths-myths)
Das, B. C., Das, S., Satpathy, S., Bose, S., Patra, R. K., Agrawal, K. C., & Bose, S. (2015). A dose-response meta-analysis reveals an anti-colorectal cancer effect of vitamin B12 for subjects with an intake above the current RDA. Journal of Cancer Research and Clinical Oncology, 141(12), 2181–2188. (https://doi.org/10.1007/s00432-015-2001-4)
Liu, K., Yang, Z., Lu, X., Zheng, B., Wu, S., Kang, J., & Sun, S. (2023). The origin of vitamin B12 levels and risk of all-cause, cardiovascular and cancer specific mortality: A systematic review and dose-response meta-analysis. Archives of Gerontology and Geriatrics, 105, 104846. (https://doi.org/10.1016/j.archger.2023.104846)
Mikkelsen, K., Apostolopoulos, V., Naumovski, N., & Laroo, C. (2021). Effects of Vitamin B12 Supplementation on Cognitive Function, Depressive Symptoms, and Fatigue: A Systematic Review, Meta-Analysis, and Meta-Regression. Nutrients, 13(3), 923. (https://doi.org/10.3390/nu13030923)
Gouffe, J., Bayer, H., Pryor, R., Dove, E. R., Skouteris, H., & Wertheim, E. H. (2021). A Systematic Review and Meta-Analysis of B Vitamin Supplementation on Depressive Symptoms, Anxiety, and Stress: Effects on Healthy and 'At-Risk' Individuals. Nutrients, 13(9), 3098. (https://doi.org/10.3390/nu13093098)
Langan, R. C., & Goodbred, A. J. (2017). Vitamin B12 Deficiency: Recognition and Management. American Family Physician, 96(6), 384–389. (https://www.aafp.org/pubs/afp/issues/2017/0915/p384.html)
Bärebring, L., Gille, A., Smedman, A., Eriksson, J., Tallkvist, J., Öhlund, I., & Andersson, H. (2022). Intake of vitamin B12 in relation to vitamin B12 status in groups susceptible to deficiency: a systematic review. Food & Nutrition Research, 66. (https://doi.org/10.29219/fnr.v66.8032)