Myths about Vitamin B12

A whole mythology has grown up around vitamin B12: it is called the "energy vitamin," injected before competitions, and added to fat burners and energy drinks. Some of these notions have a rational kernel, some are pure marketing. The editorial team checked seven of the most common claims against the scientific data.

Myths about energy and athletic performance

Myth 1: "B12 shots give energy and increase endurance."This myth has historical roots: in the mid-20th century, B12 injections were popular among athletes and even among people with no indications at all. The logic is simple — B12 is needed to form red blood cells, and therefore "more vitamin means more oxygen in the muscles."

In reality, the body uses B12 only within the limits of its need. If reserves are adequate, extra vitamin does not speed up blood formation and does not raise hemoglobin levels. Reviews devoted to vitamins in sport (Lukaski, 2004) conclude that supplements improve performance only when a person has a deficiency. The position stand of the ACSM, the Academy of Nutrition and Dietetics, and Dietitians of Canada (Thomas et al., 2016) also does not recommend vitamin supplements for athletes with normal status.

The sense of a "surge of energy" after an injection, which some people describe, is most often explained by the placebo effect or by the person actually having had a hidden deficiency. In the latter case the injection really does help, but that is treatment, not doping or a "booster."

Myth 2: "B12 burns fat and speeds up metabolism."B12 takes part in the metabolism of fatty acids with an odd number of carbon atoms and of some amino acids, but it does not increase energy expenditure. There are no randomized studies showing weight loss from B12 in people without a deficiency. Injections of "lipotropic cocktails" at weight-loss clinics are marketing, not evidence-based medicine.

Myths about B12 sources and plant-based eating

Myth 3: "Vegans can get B12 from spirulina, nori, or fermented foods."This is one of the most dangerous myths. Spirulina and some algae contain mostly so-called pseudo-vitamin B12 — analogs that tests may detect as B12 but that do not work in the human body as a coenzyme. Moreover, they can theoretically compete with the real vitamin.

B12 is synthesized only by microorganisms. Animals get it from bacteria, and this is precisely why animal products are a natural source. For people on a strict plant-based diet, the only reliable sources are supplements and fortified foods. A systematic review by Pawlak et al. (2013) showed a high prevalence of deficiency among vegetarians and especially vegans.

Myth 4: "Gut bacteria produce enough B12."Some gut bacteria do synthesize B12, but mostly in the large intestine — below the place where the vitamin can be absorbed (the ileum). Therefore this synthesis does not cover a person's needs.

Even among people who eat animal products, deficiency occurs more often than is commonly thought: in old age, with reduced stomach acidity, or during long-term drug therapy, dietary B12 is absorbed worse. So the claim "if I eat meat, I definitely have enough B12" is not always true either.

Myths about forms and absorption

Myth 5: "Methylcobalamin is the only correct form, and cyanocobalamin is a poison."The amount of cyanide released from a typical dose of cyanocobalamin is negligible and is neutralized by the body without consequences for a healthy person. Cyanocobalamin has been used in medicine for decades, and most studies of the effectiveness of oral therapy have been done on it.

A review by Obeid, Fedosov and Nexo (2015) showed that inside the cell all forms of cobalamin are first converted into a common intermediate and then into the needed coenzymes. In other words, "ready-made" methylcobalamin from a tablet has no proven advantages for preventing or treating deficiency. An exception is rare conditions, for example Leber's optic neuropathy, where a doctor chooses a different form.

Myth 6: "Tablets don't work; only injections help."For severe deficiency with neurological symptoms, injections are indeed often the first choice. But a study by Kuzminski et al. (1998) and a Cochrane review (Wang et al., 2018) showed that high oral doses can normalize B12 levels even in patients with impaired absorption — through passive diffusion, by which about 1% of the dose is absorbed.

Another widespread belief is that injections "work faster" and are therefore better for everyone. Speed matters only in severe deficiency with neurological symptoms, where the doctor aims to replenish reserves as quickly as possible. For prevention and mild deficiency, regular oral intake is more convenient, cheaper, and requires no medical procedures.

Myths about safety and tests

Myth 7: "B12 is absolutely harmless in any dose."The vitamin's toxicity is indeed very low, and no tolerable upper intake level has been established for it. But "not established" does not mean "proven safe under any conditions." In the DIVINe study (House et al., 2010), high doses of B vitamins in patients with diabetic nephropathy were associated with worse kidney function. In the VITAL cohort (Brasky et al., 2017), long-term intake of high doses of B6 and B12 was associated with an increased risk of lung cancer in male smokers.

These data are not a cause for panic, but they are an argument against taking megadoses for years without indications. For prevention, most people are served by doses commensurate with their need, or moderate doses taken less frequently.

Bonus myth: "High B12 on a test means an overdose."Elevated serum B12 is most often related to taking supplements, but it can also be a marker of liver, kidney, or blood diseases. If a person is not taking supplements and the level is high, this is a reason for examination, not for celebration.

And vice versa: a "normal" serum B12 does not always rule out deficiency at the tissue level. In doubtful cases, doctors assess methylmalonic acid, homocysteine, or holotranscobalamin (Green et al., 2017).

How to tell fact from marketing

Most myths about B12 arise from one and the same logical step: if a deficiency of the vitamin causes a certain symptom, then an excess supposedly gives the opposite effect. Deficiency causes fatigue — therefore B12 "gives energy." Deficiency impairs blood formation — therefore B12 "increases endurance." This logic does not work for most vitamins.

The second reason is the marketing of "active" and "natural" forms, which are sold at a higher price. Manufacturers refer to biochemical diagrams featuring methylcobalamin, but they do not mention that the body is able to convert other forms into the needed coenzymes.

To avoid falling into the trap, the editorial team advises asking a few simple questions of any claim:

• Are there randomized studies in humans, and not just theory or experiments on cells?
• Did the studies concern people without a deficiency, that is, people like you?
• Who funded the work and where was it published?
• Are limitations and possible risks mentioned?

If there is no answer, or the seller refers only to "reviews," then what you are looking at is probably marketing, not science.

Editorial conclusions

Vitamin B12 is a vital nutrient, and its deficiency has real, sometimes irreversible consequences. That is precisely why it is important to separate well-founded recommendations from myths.

A B12 supplement is mandatory for vegans and useful for people with confirmed deficiency or impaired absorption. For everyone else it provides neither energy, nor an athletic advantage, nor weight loss.

The form of the vitamin matters less than the dose, the regularity, and the reason for taking it. And megadoses without indications are not "insurance" but an unjustified risk.

To learn more, read our articles "Vitamin B12: available forms and which to choose," "Who should not take vitamin B12," and "What to combine vitamin B12 with."

References

1. Thomas DT, Erdman KA, Burke LM. American College of Sports Medicine Joint Position Statement. Nutrition and athletic performance. Med Sci Sports Exerc. 2016;48(3):543–568.
2. Lukaski HC. Vitamin and mineral status: effects on physical performance. Nutrition. 2004;20(7–8):632–644.
3. Pawlak R, Parrott SJ, Raj S, Cullum-Dugan D, Lucus D. How prevalent is vitamin B12 deficiency among vegetarians? Nutr Rev. 2013;71(2):110–117.
4. Obeid R, Fedosov SN, Nexo E. Cobalamin coenzyme forms are not likely to be superior to cyano- and hydroxyl-cobalamin in prevention or treatment of cobalamin deficiency. Mol Nutr Food Res. 2015;59(7):1364–1372.
5. Kuzminski AM, Del Giacco EJ, Allen RH, Stabler SP, Lindenbaum J. Effective treatment of cobalamin deficiency with oral cobalamin. Blood. 1998;92(4):1191–1198.
6. House AA, Eliasziw M, Cattran DC, et al. Effect of B-vitamin therapy on progression of diabetic nephropathy: a randomized controlled trial. JAMA. 2010;303(16):1603–1609.
7. Brasky TM, White E, Chen CL. Long-term, supplemental, one-carbon metabolism-related vitamin B use in relation to lung cancer risk in the Vitamins and Lifestyle (VITAL) cohort. J Clin Oncol. 2017;35(30):3440–3448.
8. Green R, Allen LH, Bjørke-Monsen AL, et al. Vitamin B12 deficiency. Nat Rev Dis Primers. 2017;3:17040.