Daily Vitamin B12 Tablets: What the Evidence Says

Daily B12 tablets clearly help people who are deficient or at high risk of deficiency, such as some older adults, vegans and long-term metformin users. For healthy people with adequate B12 status, additional benefits for energy, memory or mood are unproven. This Tanrub evidence review covers Australian and American intake recommendations, the research on supplement benefits and when a healthcare professional may recommend tablets or injections.

Australian versus American vitamin B12 recommendations

Australia and the US use the same daily adult vitamin B12 requirements. Australia calls them Recommended Dietary Intakes (RDIs); the United States calls them Recommended Dietary Allowances (RDAs).

mcg (or µg) means micrograms; 1 mg equals 1,000 mcg. These are daily dietary requirements, not recommended treatment doses. Neither country has set a formal tolerable upper intake level because of B12’s low apparent toxicity. This is not a recommendation to take unlimited or unnecessarily high doses. Sources: Australian Government Nutrient Reference Values and US NIH Office of Dietary Supplements.

What vitamin B12 does and how tablets are absorbed

Vitamin B12 is needed for developing and insulating the nervous system, forming healthy red blood cells and making DNA. It works as a helper (cofactor) for two enzymes, one of which converts homocysteine into methionine (NIH Office of Dietary Supplements).

B12 in food is attached to protein and must first be freed by stomach acid and enzymes. It then binds a stomach-made carrier called intrinsic factor and is absorbed in the last part of the small intestine. Tablets contain B12 in free form, so they skip the first step, and absorption from supplements is about 50% higher than from food (NIH ODS).

There is a catch: intrinsic factor can only carry so much. Absorption is about 50% at doses under 1 to 2 mcg, but falls to roughly 2% at 500 mcg and 1.3% at 1,000 mcg. A little B12 is also absorbed passively without intrinsic factor, which is why very large doses still work (NIH ODS; American Family Physician).

The body stores substantial B12, so deficiency can develop over years. However, gradual onset can delay diagnosis, particularly when neurological symptoms appear without anaemia.

Who benefits most from a daily tablet?

Benefit is clearest where dietary intake is inadequate or absorption is impaired. Risk alone does not establish deficiency; appropriate testing considers symptoms and clinical context. A 2026 Australian Prescriber review cites B12 deficiency in approximately 5.2–6.3% of Australians older than 50, depending on population and criteria.

Sources: Australian Prescriber (2026); NIH fact sheet.

Preventing and correcting B12 deficiency

This is the best-established benefit. Deficiency can cause megaloblastic anaemia (abnormally large red blood cells), low white cell and platelet counts, fatigue, palpitations, pale skin, a sore tongue and weight loss. It can also cause numbness and tingling in the hands and feet, and in some people dementia and infertility (NIH ODS).

The nerve symptoms can appear without anaemia, so a normal blood count does not rule deficiency out, and early treatment matters because nerve damage can become irreversible (NIH ODS).

A daily tablet is also a practical way to prevent the problem in at-risk groups. The Mayo Clinic notes that supplements at recommended doses are generally considered safe (Mayo Clinic).

Australian testing guidance: Total serum B12 is often the first test. Active B12 (holotranscobalamin), methylmalonic acid or homocysteine may help when results are inconclusive. Australian laboratories often report B12 in pmol/L, whereas US articles often use pg/mL; cut-offs depend on the test and laboratory. Neurological deficiency may occur without anaemia. Test results need to be interpreted alongside symptoms and risk factors. Source: Australian Prescriber.

Tablets versus injections

Injections have long been the standard treatment, but high-dose daily tablets look like a workable alternative for many people. A 2018 Cochrane review pooled three trials covering 153 people (74 on tablets, 79 on injections). In two trials using 1,000 mcg a day orally, B12 levels did not differ from injections, and a third trial using 2,000 mcg a day produced higher blood levels with tablets (Cochrane).

Later work points the same way. A 2020 Spanish trial of 283 people over 65 compared oral and intramuscular B12, and a small Swiss trial found no significant difference in normalising levels at 28 days (American Family Physician 2022).

The 2018 Cochrane review included just three studies with 153 participants; the certainty of the evidence was low or very low. Similar measured B12 blood levels in some trials do not prove that tablets and injections work equally well for every underlying cause or for serious neurological symptoms. Source: Cochrane evidence review.

Important treatment distinction: Australian Prescriber recommends intramuscular B12 for severe symptomatic deficiency with neurological involvement and lifelong intramuscular hydroxocobalamin for specified irreversible malabsorption, including pernicious anaemia, autoimmune gastritis, total gastrectomy and terminal ileum resection. Oral treatment is generally preferred for purely dietary insufficiency; some other patients can use high-dose oral replacement under supervision with follow-up testing. Do not switch prescribed injections to tablets without medical advice. Source: Australian Prescriber treatment guidance.

Pregnancy, breastfeeding and infant development

In pregnant and breastfeeding women, B12 deficiency may cause neural tube defects, developmental delay, failure to thrive and anaemia in the baby. Exclusively breastfed infants of vegan mothers can have very small B12 reserves and develop deficiency early (NIH ODS).

Several lines of research support this concern:

• A 2025 meta-analysis found mothers of babies with neural tube defects had lower B12, and the link held even when folate levels did not differ (Wu et al., Nutrients 2025).

• An Irish study with no folic acid fortification found deficient or inadequate maternal B12 was linked to a significantly higher neural tube defect risk (Molloy et al.).

• In the PRIYA randomised trial in India, B12 given before conception improved maternal B12 status and the children’s neurodevelopment at 2 years (Frontiers in Pediatrics).

• A trial in South India found 50 mcg a day of oral B12 from 14 weeks of pregnancy improved breast milk B12, infant status and infant cognitive function at 30 months (reported in the same paper).

The evidence is not one-sided. In a Spanish cohort, better maternal B12 early in pregnancy was linked to better infant motor, language and cognitive scores at 40 days, but another study of children aged 6 to 8 found no association with second-trimester B12 (ECLIPSES study). A review also noted that only one randomised trial of B12 supplementation during pregnancy had been done at the time (maternal B12 review), and the PRIYA population had very high deficiency rates, so results may not transfer to well-nourished women.

Folic acid remains the proven way to prevent neural tube defects. Whether to add B12, and how much, is a question for an antenatal care provider.

For pregnant or breastfeeding people on vegan diets, an adequate reliable B12 source is especially important. Folate and folic acid guidance to prevent neural tube defects remains essential and is not replaced by B12. Discuss supplements and testing with an antenatal care provider.

Memory, mood and energy: what studies show

This is where supplement marketing can exceed evidence. Correcting an actual deficiency can help symptoms caused by that deficiency, but extra B12 has not been shown to improve energy or cognition in people whose status is already adequate.

These summaries reflect the evidence discussed in the NIH professional fact sheet, including controlled trials and systematic reviews.

Safety: heart health and the cancer question

Heart disease. B12 helps lower homocysteine, a marker linked to heart disease, so researchers hoped supplements would protect the heart. They do not appear to. A Cochrane review of 15 studies (71,422 people) concluded B12 alone or with other B vitamins does not prevent heart attacks or reduce deaths in people at risk of or with cardiovascular disease (NIH ODS).

Cancer. The picture is mixed and often misread:

• A study of 757,185 people found higher cancer risk in the year after a blood B12 above 813 pg/mL, and long-term supplement use of at least 55 mcg a day was linked to 40% higher lung cancer risk in men but not women in the VITAL cohort (NIH ODS).

• A meta-analysis of 18 randomised trials (74,498 people) found B vitamin supplements, including 20 to 2,000 mcg of B12 a day, had little or no effect on cancer incidence, cancer deaths or overall deaths over 2 to 7.3 years (NIH ODS).

• A scoping review found no evidence that high blood B12, high intake or pharmacological doses cause cancer. Cancer can itself raise blood B12, which makes the association look causal when it may run the other way (Scoping review).

Safety: Neither Australia nor the United States has established a formal upper intake level for vitamin B12, but higher doses are not necessarily better. Associations between high blood B12 and cancer in observational studies do not prove that B12 causes cancer, because illness itself can affect measured B12 concentrations. Persistently high B12 without supplementation should be discussed with a clinician. Source: NIH B12 fact sheet.

Practical guide: dose, form, food and testing

Dose. Multivitamins typically hold 5 to 25 mcg of B12, B-complex products 50 to 500 mcg, and B12-only tablets 500 to 1,000 mcg (NIH ODS). Because absorption drops steeply above about 1 to 2 mcg, a bigger tablet gives a smaller share absorbed, but the high-dose passive route is what makes 1,000 to 2,000 mcg a day work for treating deficiency.

Form. Cyanocobalamin is the most common form, and the body converts it to the active forms. No evidence shows absorption differs between forms, and sublingual tablets and lozenges work no better than swallowed ones (NIH ODS).

Food first, where possible. The following figures are approximate and vary by serving and brand, adapted from the NIH/USDA food table.

Plant-based diets require special attention to reliable fortified food or supplements. Fortification of nutritional yeast and plant milks varies by product.

Testing: Discuss symptoms or risk factors with a clinician; total serum B12 is commonly the first test in Australia, with other markers used as needed. Do not treat numbness, tingling, worsening balance or other neurological symptoms with over-the-counter tablets alone: these warrant prompt medical assessment.

What should readers remember?

1. Daily B12 needs are the same for adults in Australia and the United States.
2. Supplementing to prevent or correct deficiency is evidence-based; routine megadoses for extra energy are not.
3. Vegans need a reliable source of B12 from supplements or fortified foods.
4. High-dose tablets can be appropriate for certain deficiencies, but injections remain recommended for severe neurological deficiency and some permanent absorption disorders.
5. Choose testing and doses according to individual health circumstances rather than marketing claims.

Also read Tanrub’s Daily Vitamins: What the Evidence Shows and Daily Vitamin C Tablets: What the Evidence Shows.

Sources and editorial note

Research reviewed on 12 October 2026. Core sources: Australian Government: Vitamin B12 nutrient reference values; NIH: Vitamin B12 health professional fact sheet; Australian Prescriber (2026): Vitamin B12 deficiency testing and treatment; and Cochrane: oral versus intramuscular vitamin B12 (2018).

Additional evidence discussed in the original article includes the PRIYA and ECLIPSES maternal B12 studies, Niklewicz et al. (2024) on vegans, Burgstaller et al. (2021) on cognition, depression and fatigue, and studies on metformin, cardiovascular outcomes and cancer. These secondary claims were not all independently checked against full texts. Tanrub is presenting a research summary, not a clinical review or hands-on supplement test.

General information only, not medical advice. Consult a doctor or pharmacist before starting a supplement if pregnant, taking regular medication or dealing with a health condition.