Vitamin B12 and Energy: Who Benefits and Who's Wasting Money

For someone who already gets enough B12 from food, the US National Institutes of Health’s Office of Dietary Supplements (ODS) says extra B12 brings no added energy or endurance.¹ The link between vitamin B12 and energy runs the other way: when the body runs short of B12, people can develop a type of anemia that makes them tired and weak, and replacing the vitamin treats it.

That split decides whether a bottle of B12 or a clinic shot is worth the money, and B12 is widely sold for everyday energy to many people who are unlikely to notice a difference. Three checks sort you into one camp or the other: whether you belong to a risk group (the table below), whether you have the signs that guidelines pair with those risks, and what a blood test taken before any supplement shows. If the test is normal, a guide to what else makes people tired all the time, with a list to take to the doctor is a more useful next step.

What vitamin B12 does for your blood and nerves

Vitamin B12 helps the body make working red blood cells and keeps the nervous system healthy, according to the UK’s NHS. Short of it, the body produces red blood cells that are abnormally large and cannot work properly, and since red blood cells carry oxygen around the body, the result is extreme tiredness and a lack of energy.²

A 2020 narrative reviewnarrative review: A review in which an expert summarizes a body of research in prose, choosing which studies to discuss. It can be a good map of a field, but without a stated search and pooling method it is easier for selection and opinion to shape the conclusions than in a systematic review.Full entry in the glossary in the journal Nutrients, funded by the drug and consumer-health company Sanofi, where four of its five authors worked, traces B12’s part in the reactions that turn food into usable energy inside cells. It links a shortage to fatigue, breathlessness and poor exercise tolerance, as well as nerve damage, memory problems and low mood.³

The tiredness builds slowly. The NHS says B12 stores can last around 2 to 5 years without being topped up, so problems may appear long after a change of diet.⁴ A person who went vegan three years ago without fortified foods or a supplement may have felt fine most of that time and only now notice that stairs leave them breathless. So B12 is worth considering when tiredness creeps in and you belong to a risk group, even years after a diet change or a new medicine.

Vitamin B12 and energy: does a supplement give you a boost?

Vitamin B12 gives you energy only if you were short of it. ODS notes that B12 is often promoted as an energy enhancer and endurance booster because of its role in energy metabolism, but its fact sheet for health professionals says supplements appear to have no benefit for performance without a nutritional deficit.⁵

Trials in people with normal levels are scarce, and the one this article could read in full is more than 50 years old.

The study

Limited evidence

B12 or dummy shots for tiredness with no known cause (Ellis and Nasser, England, 1973)

In this crossover trialcrossover trial: A trial in which each participant receives every condition being compared, one after another in random order, often with a gap between them. Because people are compared with themselves, fewer are needed, but the design only suits effects that wear off.Full entry in the glossary, adults with tiredness that had no known cause, all with normal blood tests, had 2 weeks of B12 injections and 2 weeks of matching dummy injections, in random order. Of 48 who started, 19 dropped out or were excluded, and only the 14 given the dummy course first could be compared, because the vitamin’s effect seemed to carry over. In that group, well-being and happiness ratings favored B12; fatigue, appetite and sleep ratings did not clearly differ between the vitamin and dummy courses. The authors called for further trials.⁶

With so few people and ratings marked on paper cards, the pilot cannot outweigh the NIH’s current reading of the evidence. A 2021 systematic review from the University of Zurich, with no outside funding, left the pilot out for high risk of bias and found only one trial, of a B-vitamin mix, that reported on unexplained fatigue: too little evidence to draw conclusions.⁷

Labels sold in Europe often say that B12 “contributes to the reduction of tiredness and fatigue”. That sentence is on the EU’s list of permitted health claims, which the UK kept after Brexit, and any food that is at least a source of B12 may carry it.⁸ It describes what the vitamin does as a nutrient, and says nothing about taking more than you need. On a shelf, judge a B12 product by whether you are likely to be short of the vitamin; the label line is the same on every bottle.

Myth

A B12 supplement gives anyone a quick energy boost.

Fact

The NIH supplement office says B12 adds no energy or endurance for people who get enough from their diet. It relieves tiredness caused by a deficiency.

Who is at risk of vitamin B12 deficiency?

People at risk of vitamin B12 deficiency either take in too little or absorb too little. A 2024 guideline from England’s National Institute for Health and Care Excellence (NICE) names the main groups: people who eat few or no animal foods, people with pernicious anemia or other gut conditions, people who have had gut surgery, and people taking certain medicines or using nitrous oxide recreationally.⁹

Absorption takes two steps, ODS explains. Stomach acid frees B12 from the protein it is attached to in food; the vitamin then binds to intrinsic factor, a protein made by the stomach, and the two are absorbed together. Supplements skip the first step but still need intrinsic factor.¹ Each risk group breaks the route at a different point.

Babies breastfed by mothers who eat no animal foods can also run short early in life, ODS notes, sometimes when the mother’s own deficiency is too mild to notice.⁵

The UK’s medicines regulator, the MHRA, advises people on metformin to seek medical advice for new or worsening extreme tiredness, a sore red tongue, pins and needles, or pale or yellow skin, and not to stop metformin without talking to their doctor.¹⁰ If you take an acid-reducing medicine long term, ask about B12 at your next review instead of stopping the tablet on your own.

What are the signs of low vitamin B12?

Low vitamin B12 usually shows up gradually as extreme tiredness and lack of energy, often with pins and needles, a sore red tongue, mouth ulcers, muscle weakness, vision problems, or changes in memory and mood, the NHS says. Some of these can happen even without anemia, and the longer a deficiency goes untreated, the higher the chance of permanent damage.¹¹

None of these signs is specific to B12, so NICE’s guideline pairs them: it advises offering a test to someone with at least one common symptom, unexplained fatigue and “brain fog” among them, and at least one common risk factor. It also tells doctors not to rule out B12 deficiency just because a blood count shows no anemia, to take blood before B12 treatment starts, and to ask about over-the-counter B12, which can raise the result without fully treating a deficiency.⁹

A 70-year-old who has taken an acid-reducing tablet for years and now feels unsteady on the stairs fits that pattern. A 30-year-old with a mixed diet who is drained after a month of late nights fits half of it, and sleep is the likelier culprit.

If both are true, ask a doctor about a test before buying anything. A test after weeks of self-treatment can look reassuring when it is not.

1. 1A sign plus a risk factorNICE: offer a B12 test
2. 2Blood taken firstbefore any B12 treatment
3. 3Result read against thresholdsdeficiency confirmed, possible or unlikely
4. 4Next steptreat by cause, test further, or look for another cause

Doctors outside England follow national guidance that may use different tests and cut-offs.

How doctors treat a confirmed B12 deficiency

A confirmed vitamin B12 deficiency is treated with B12 tablets or injections, chosen by a doctor according to the cause. NICE’s 2024 guideline says replacement works for most people, though some need it for life: it recommends lifelong injections when autoimmune gastritis or a total gastrectomy stops the gut absorbing B12, considering tablets when diet is the cause, and either route when a medicine is. It also advises seeking help without waiting for a booked appointment if symptoms do not improve, get worse or come back.⁹

The NHS describes injections every other day at first, given by a GP or nurse, then either tablets or regular injections; people whose deficiency is not diet-related usually have an injection every 2 to 3 months for life. In the UK, hydroxocobalamin is preferred for injections because it stays in the body longer.¹² Other countries may use other forms and schedules, and your doctor will follow local guidance.

Tablets may match injections for raising blood levels. A 2018 Cochrane review found three small randomized trials comparing high-dose oral B12 with injections in people with a deficiency; tablets normalized blood levels about as well, but the evidence was rated low quality and no trial reported on symptoms such as tiredness.¹³ If regular injections are hard to fit around work or travel, ask whether tablets suit the cause of your deficiency, since the guideline ties the route to why your levels fell.

Should I take B12 if I am always tired?

Taking B12 for tiredness makes sense when a deficiency is likely, and a test should come first. Without risk factors or symptoms that point to B12, the evidence above offers little reason to expect a supplement to help, and the money is better spent finding the cause. When the test is normal, NICE advises doctors to look for other causes and to consider repeating it after 3 to 6 months if symptoms continue.⁹

Prevention is a different matter. B12 is found in meat, fish, milk and other dairy foods and eggs, and some yeast extracts, breakfast cereals and soy products are fortified with it, the NHS says, and people who find it hard to get enough from food, such as vegans, may need B12 tablets for life.¹² For anyone who eats no animal foods, a reliable source of B12 belongs in the diet itself, alongside the wider advice on food choices that keep energy level through the day.

Are B12 injections worth it?

B12 injections are worth it when a doctor prescribes them for a diagnosed deficiency, especially in people who cannot absorb the vitamin from the gut. For healthy people seeking an energy lift, the UK’s Advertising Standards Authority concluded in a December 2023 ruling on an IV drip clinic, whose energy drip contained B12 among other nutrients, that the evidence did not support claims that a B12 infusion could raise energy in generally healthy people.¹⁴

The UK’s Committee of Advertising Practice adds that evidence about treating a deficiency is unlikely to support such claims, and that prescription-only vitamin injections, B12 among them, cannot be advertised to the public in the UK.¹⁵ In the US, injected B12 is also a prescription medicine, ODS notes.⁵ Who may sell and advertise B12 shots is set nationally, and elsewhere your own medicines or advertising regulator sets the rules.

For a healthy person with normal levels, a wellness-clinic course therefore buys no proven benefit. Before booking, ask whether the clinic tests your B12 level first and what it will do if the result is normal.

Getting a B12 check: how soon, and with which symptoms

Nerve symptoms such as numbness or balance problems need an appointment within days, as does lasting tiredness in someone with a risk factor; risk factors alone are worth raising at a routine review. The tiers below draw on NHS, NICE, UK regulator and crisis-service advice; health services elsewhere may sort them differently.

• Immediately: for sudden symptoms that could be a stroke or heart attack, or any other life-threatening emergency, call your local emergency number. In the UK that is 999, and NHS 111 is there for anyone unsure whether to call it.¹⁶ For thoughts of suicide or self-harm, whatever their cause, contact emergency services or a crisis line straight away: 988 takes calls and texts in the US, Samaritans answer on 116 123 in the UK and Ireland, and Find A Helpline lists free lines in other countries.¹⁷¹⁸¹⁹
• Soon, within days: numbness, pins and needles, unsteadiness, vision problems or confusion that build up gradually, or tiredness lasting weeks together with a risk factor from the table. NICE advises offering a test in the second case, and tells doctors not to delay B12 treatment in suspected megaloblastic anemia with nerve symptoms.⁹
• At your next review: long-term metformin or acid-reducer use, a vegan diet during pregnancy or breastfeeding, or past stomach or bowel surgery. The MHRA advises considering periodic B12 checks for people on metformin who have other risk factors.¹⁰

The bottom line

Vitamin B12 restores energy when tiredness comes from a shortage, and the evidence shows no extra lift when levels are normal. If you are tired and belong to a risk group, ask a doctor for a B12 test before you buy a supplement or a clinic shot, and mention any B12 you already take.