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Excess vitamin B12 is a topic that is often surrounded by confusion and myths. While this vitamin is essential for the proper functioning of the body, including the production of red blood cells and the maintenance of neurological health, concerns sometimes arise about its effects if overconsumed. Some worry that high levels of B12 can lead to health problems, ranging from acne to increased risks of certain diseases.
Misconceptions about excess B12
Before we get into the nitty-gritty, let's start by clearing up a few 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 boost energy excessively”
Unfortunately not! Even in high doses, B12 does not provide "superpowers" (Guzman-Venegas et al., 2022). It just helps correct deficiencies and ensure 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 may reduce the risk of colorectal cancer, especially at high doses (Das et al., 2015). But more studies are still needed.
You see, B12 is not the evil witch that is sometimes described! But then, what are the real risks of an excess? That's what we're going to see now.
When should you be wary of excess B12?
There is no need to panic, a simple temporary excess of B12 through food does not present any danger. This vitamin is water-soluble, so the surplus is simply eliminated in the urine.
However, persistently elevated blood levels can sometimes indicate an underlying health problem, as a 2023 meta-analysis of 22 studies and over 92,000 participants found (Liu et al., 2023):
🔴 A serum vitamin B12 level greater than 600 pmol/L (approximately 800 ng/L) was associated with a 50% increased risk of all-cause mortality.
🔴 A level between 400 and 600 pmol/L was also linked to a 34% increase in the risk of mortality.
These numbers 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 condition such as:
- Liver dysfunction
- Chronic renal failure
- Certain cancers (particularly hematological)
- Autoimmune or inflammatory diseases
So in case of a persistently high level, it is better to consult to look for the cause rather than panic. B12 is only the messenger, not the problem itself! In addition to this, correlation does not necessarily mean causation, so these results should be taken with a pinch of salt while waiting for more in-depth studies.
At what doses is B12 safe?
Fortunately, the usual nutritional intake of B12 is well below the risk thresholds. According to health authorities, the daily requirements are (ANSES, 2016):
- 2.4 μg/day for adults
- 2.6 μg/day for pregnant women
- 2.8 μg/day for lactating women
These small doses, easily covered by a balanced diet rich in animal products (meat, eggs, dairy products) or fortified foods, help maintain adequate body reserves of B12.
Even with supplementation, you really have to push the dose to reach worrying levels. Most supplements do not exceed 1000 μg per dose, which is 400 times the requirement! And a recent meta-analysis reported no concerning side effects up to doses of 2000 μg per day (Mikkelsen et al., 2021).
So except in very specific cases (medical treatments, specific illnesses), it is almost impossible to reach dangerous B12 levels by simple oral supplementation at standard doses.
As you will have understood, a punctual and moderate excess of B12 is not to be feared. But what about the possible benefits of a B12 supplement?
B12 supplementation: for whom and in which cases?
As with any supplementation, the benefits of B12 intake depend greatly on the initial situation. Clearly, it's all a question of balance!
For people with deficiencies
If your B12 stores are low, for example due to an overly restrictive diet or absorption problems, supplementation can be an excellent option for:
✅ Prevent anemia
✅ Fight against fatigue
✅ Preserve neurological and cognitive functions A 2021 meta-analysis also showed that B12 supplementation could improve depressive symptoms and stress in people who are deficient or at risk (Gouffe et al., 2021).
For the elderly
With age, B12 absorption becomes less efficient due to a decrease in hydrochloric acid production and intrinsic factors in the stomach. Moderate supplementation (a few hundred μg per day) can then be recommended from the age of 50 to prevent deficiencies (Langan et al., 2017).
For strict vegans and vegetarians
Since animal products are the main sources of B12, total exclusion diets expose individuals to a high risk of deficiency. B12 supplementation is essential for these individuals, usually at doses of 25–100 μg per day (Bärebring et al., 2022).
For the rest of the population
If you do not belong to any of these risk groups and your diet is balanced, there is no need to worry about B12 supplementation. Unless otherwise advised by a doctor, your dietary intake is more than enough to cover your needs! As you will have understood, B12 is a precious friend that you should neither have too much nor too little. The main thing is to find the right balance, depending on your lifestyle and your state of health.
Scientific references
Anses (2016). Updating the PNNS benchmarks: revision of food consumption benchmarks. 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, ER, Skouteris, H., & Wertheim, EH (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)
