Vitamin B12 plays an important part in several everyday processes in the body, including normal red blood cell formation and the healthy functioning of the nervous system. It also contributes to normal energy metabolism and the reduction of tiredness and fatigue.
It occurs naturally mainly in foods such as meat, fish, eggs and dairy products. People following a vegan diet therefore need a reliable source from fortified foods or an appropriate supplement.
Although B12 is often associated with energy, it is not a stimulant or instant energy booster. Taking more may make no noticeable difference when your existing intake is already adequate.
What is vitamin B12?
Vitamin B12 is a water-soluble vitamin also known as cobalamin. It is one of eight recognised B vitamins.
Unlike many other water-soluble vitamins, B12 can be stored in the body. A low dietary intake may therefore take time to become apparent.
Vitamin B12 has several recognised nutritional functions. It should not, however, be presented as preventing, treating or curing a medical condition.
What is vitamin B12 good for?
The Great Britain Nutrition and Health Claims Register lists the authorised claims that may be used commercially when a food or supplement supplies enough vitamin B12 to meet the applicable conditions.
Vitamin B12 contributes to:
- Normal energy-yielding metabolism
- Normal functioning of the nervous system
- Normal psychological function
- Normal red blood cell formation
- Normal homocysteine metabolism
- The normal function of the immune system
- The reduction of tiredness and fatigue
- The process of cell division
These are maintenance and nutritional-function claims. They do not mean that taking large amounts of B12 provides additional benefits or treats a diagnosed deficiency.
Vitamin B12 and normal energy metabolism
Vitamin B12 contributes to normal energy-yielding metabolism. This means it has a role in the processes that allow the body to release and use energy from food.
Vitamin B12 does not contain calories and is not a stimulant. A capsule, tablet or liquid should not be expected to work like caffeine or provide an immediate burst of energy.
Someone with an adequate B12 intake may notice no obvious difference after taking an additional supplement. If tiredness is caused by poor sleep, stress, iron deficiency, medication or another medical condition, taking B12 may not address the cause.
For a wider comparison of B12, B complex, magnesium, vitamin C and iron, read our guide to supplements for energy and tiredness.
Does vitamin B12 reduce tiredness?
Vitamin B12 contributes to the reduction of tiredness and fatigue when a food or supplement provides a qualifying amount.
This authorised claim does not mean that B12 will improve every type of tiredness. Tiredness may be connected with:
- Insufficient or disrupted sleep
- Stress or low mood
- Iron or folate deficiency
- Thyroid problems
- Diabetes
- Medication
- Infection or illness
- Other medical conditions
Speak to a GP if tiredness has lasted several weeks, affects everyday activities or occurs with other unexplained symptoms.
Vitamin B12 and red blood cells
Vitamin B12 contributes to normal red blood cell formation.
Red blood cells carry oxygen around the body using haemoglobin. When vitamin B12 deficiency affects red blood cell production, it can result in vitamin B12 deficiency anaemia.
Possible symptoms of vitamin B12 or folate deficiency can include:
- Extreme tiredness
- Lack of energy
- Muscle weakness
- Breathlessness
- Noticeable heartbeats
- A sore or red tongue
- Problems with memory or concentration
These symptoms can have several causes. Diagnosis may require a review of symptoms, medical history and blood-test results.
Vitamin B12 and the nervous system
Vitamin B12 contributes to normal functioning of the nervous system.
A deficiency may be associated with neurological symptoms including:
- Pins and needles
- Numbness
- Muscle weakness
- Balance or walking problems
- Vision changes
- Changes in memory, understanding or judgement
Some neurological symptoms can occur without anaemia. This is why suspected deficiency should be assessed rather than diagnosed solely from tiredness or a home supplement trial.
Vitamin B12 and psychological function
Vitamin B12 contributes to normal psychological function.
This authorised nutritional function should not be interpreted as a claim that B12 treats depression, anxiety, dementia, poor concentration or another mental health condition.
Mood, memory and concentration changes can have numerous causes. Seek medical advice when these symptoms are persistent, unexplained or worsening.
Does vitamin B12 support the immune system?
Vitamin B12 contributes to normal immune-system function when a qualifying amount is supplied.
This does not mean that a high-dose B12 supplement prevents infections or provides an “immune boost”. Supplements should not replace vaccination, sleep, a balanced diet or medical care.
Which foods contain vitamin B12?
Good natural sources of vitamin B12 include:
- Meat
- Fish
- Eggs
- Milk
- Cheese
- Other dairy products
Vitamin B12 may also be added to:
- Fortified breakfast cereals
- Fortified plant-based drinks
- Fortified nutritional yeast
- Yeast extracts
- Some fortified meat alternatives
Check the nutritional panel because not every cereal, plant drink or meat alternative contains vitamin B12.
How much vitamin B12 do adults need?
NHS guidance on vitamin B12 states that adults aged 19 to 64 need approximately 1.5 micrograms per day.
People who regularly eat meat, fish or dairy products should usually be able to obtain enough through their diet. However, individual requirements and absorption can vary, and the amount on a supplement label should not be confused with the amount the body ultimately absorbs.
Do not assume that the product with the largest number is automatically the best option.
Can vegans obtain vitamin B12 from food?
Vitamin B12 is not naturally found in fruit, vegetables or grains. People following a vegan diet need a dependable source through fortified foods or an appropriate supplement.
The updated NHS vegan diet guidance lists possible sources including:
- Breakfast cereals fortified with B12
- Unsweetened soya drinks fortified with B12
- Fortified yeast extract
- Fortified nutritional yeast flakes
Check labels regularly because manufacturers can change fortification levels and formulations.
Who may need to pay particular attention to vitamin B12?
People following vegan diets
Vegans may have a low dietary intake when they do not regularly consume fortified foods or a suitable supplement.
Vegetarians who eat limited eggs or dairy
Vegetarians who regularly eat dairy products and eggs may obtain enough B12, but intake can be lower when these foods are rarely consumed.
Older adults
Some older adults have more difficulty absorbing naturally occurring B12 from food. A healthcare professional can advise whether testing or supplementation is appropriate.
People with pernicious anaemia or autoimmune gastritis
Pernicious anaemia is associated with an autoimmune process that affects the stomach and prevents adequate absorption of vitamin B12. It requires medical treatment rather than reliance on an ordinary food supplement.
People with digestive conditions
Conditions affecting the stomach or intestines may interfere with vitamin B12 absorption. These can include Crohn’s disease and conditions affecting the part of the small intestine where B12 is absorbed.
People who have had stomach or bowel surgery
Operations involving the stomach or terminal part of the small intestine can reduce absorption and may result in a need for long-term monitoring or replacement.
People taking certain medicines
Some medicines can affect B12 absorption or levels, including metformin and proton-pump inhibitors. Do not stop prescribed medicine without advice. Your GP or pharmacist can advise whether monitoring is needed.
People exposed to nitrous oxide
Nitrous oxide can interfere with the way the body uses vitamin B12. Anyone experiencing neurological symptoms after nitrous-oxide use should seek medical advice promptly.
The NHS guide to B12-deficiency causes provides more information about dietary, absorption-related and medicine-related factors.
Is vitamin B12 the same as vitamin B complex?
No. Vitamin B12 is one individual B vitamin. A vitamin B complex normally contains several—and often all eight—B vitamins.
A B complex generally includes:
- Thiamin
- Riboflavin
- Niacin
- Pantothenic acid
- Vitamin B6
- Biotin
- Folate
- Vitamin B12
A standalone B12 product provides a more targeted option, while a B complex provides several B vitamins in one formula. Neither is universally better.
Our vitamin B complex versus B12 comparison explains how their ingredients, label checks and suitability differ.
Which forms of vitamin B12 are used?
Common vitamin B12 forms include:
- Cyanocobalamin
- Methylcobalamin
- Hydroxocobalamin
Cyanocobalamin and methylcobalamin are commonly seen in food supplements. Hydroxocobalamin is commonly used in prescribed B12 injections in the UK.
A more expensive or heavily marketed form is not automatically superior. Suitability depends on the amount, product format, reason for using it, ability to absorb it and any professional advice received.
Which vitamin B12 supplement format is best?
Vitamin B12 is available as:
- Tablets
- Capsules
- Liquid drops
- Oral sprays
- Chewable tablets
- Lozenges
- Sublingual products
- Adhesive patches
No format is automatically best for everyone. Compare:
- The amount per complete daily serving
- The form of vitamin B12
- How the product is used
- The complete ingredient list
- Vegan or vegetarian suitability
- Sugar, sweeteners and flavourings
- Storage instructions
- Evidence for the delivery method
The current Vitamin B12 + B Complex Drops are an example of a combined liquid B-vitamin product rather than standalone B12. Compare the complete label and serving rather than relying on the product name or assuming that liquid automatically means faster absorption.
Our detailed vitamin B12 drops versus patches guide explains why oral drops and transdermal patches should not be assumed to have the same evidence base.
Does vitamin B12 give you instant energy?
No. Vitamin B12 contributes to normal energy metabolism but is not a stimulant.
Someone receiving appropriate treatment for a diagnosed deficiency may experience an improvement in deficiency-related symptoms over time. This should not be turned into a general promise that a retail B12 supplement provides instant or all-day energy.
Someone who already obtains enough vitamin B12 may take an additional supplement without noticing a difference.
How long does vitamin B12 take to work?
There is no universal timeframe. It depends on:
- Whether a deficiency is present
- The cause and severity of any deficiency
- The ability to absorb B12
- The treatment or supplement being used
- Whether the nervous system is affected
- Whether symptoms have another cause
For medically diagnosed deficiency, read our separate guide explaining vitamin B12 deficiency recovery times. Do not use an ordinary product label as a replacement for a prescribed treatment plan.
What should you check before buying vitamin B12?
The amount per complete serving
B12 is usually displayed in micrograms, written as mcg or µg. Do not confuse micrograms with milligrams.
The form of B12
Check whether the label lists cyanocobalamin, methylcobalamin or another permitted form. Assess this alongside the amount and format rather than in isolation.
Whether it is standalone or combined
A product described as “B12” may also contain vitamin B6, folate, vitamin C, botanicals or other ingredients. Check the complete nutritional panel.
Dietary suitability
Do not assume that every B12 product is vegan. Check the capsule shell, flavourings, carrier ingredients and explicit suitability statement.
The instructions and warnings
Follow the labelled serving and storage instructions. Do not exceed the recommended amount. Current GOV.UK food supplement guidance also advises checking that health claims used on products are authorised.
Duplicated ingredients
Check multivitamins, B complexes, magnesium formulas, fortified drinks and other supplements for duplicated B12, vitamin B6 or folate.
Can vitamin B12 deficiency be self-diagnosed?
No. Tiredness, weakness, pins and needles and memory changes can have several causes.
The NHS overview of vitamin B12 and folate deficiency explains that diagnosis may involve symptoms and blood-test results. Further investigation may be needed to identify why B12 levels are low.
A diagnosed deficiency may require tablets or injections depending on its cause. Do not replace prescribed treatment with a retail B12 product or B complex.
When should you speak to a GP?
Seek medical advice if you experience:
- Persistent or unexplained tiredness
- Pins and needles
- Numbness
- Muscle weakness
- Balance or walking problems
- Changes in memory or concentration
- A sore or red tongue
- Vision changes
- Symptoms that are becoming worse
Prompt assessment matters because certain neurological problems associated with prolonged B12 deficiency may become irreversible.
Frequently asked questions
What is the main function of vitamin B12?
Vitamin B12 has several functions rather than one main purpose. It contributes to normal energy metabolism, red blood cell formation, nervous-system function, psychological function and the reduction of tiredness and fatigue.
Does vitamin B12 help you feel less tired?
Vitamin B12 contributes to reducing tiredness and fatigue when a qualifying amount is supplied. It may not make a noticeable difference when tiredness has another cause or existing B12 intake is already adequate.
Is vitamin B12 important for vegans?
Yes. Reliable natural plant sources are limited, so vegans need B12 from fortified foods or an appropriate supplement.
Is vitamin B12 better than a B complex?
Neither is automatically better. Standalone B12 provides one targeted vitamin, while a B complex supplies several B vitamins. The appropriate choice depends on your diet and existing supplement routine.
Is methylcobalamin better than cyanocobalamin?
The form name alone does not establish that a product is better. Compare the amount, complete formulation, delivery method and individual suitability.
Can vitamin B12 be taken every day?
Many B12 food supplements are designed for daily use. Follow the directions on the specific label or the instructions provided by your healthcare professional.
Final answer
Vitamin B12 contributes to normal energy metabolism, red blood cell formation, nervous-system function, psychological function, immune-system function and the reduction of tiredness and fatigue.
It is found naturally mainly in meat, fish, eggs and dairy products. People following vegan diets need a reliable source through fortified foods or an appropriate supplement.
Vitamin B12 should not be expected to provide instant energy when your intake is already adequate. Persistent tiredness, pins and needles, weakness, balance problems or memory changes should be investigated rather than managed solely with supplements.
To compare available B-vitamin formats and complete ingredient labels, explore the Energy & Performance collection without treating a retail supplement as a substitute for diagnosis or prescribed treatment.