Vitamin B12 is an essential nutrient that helps support normal energy metabolism, red blood cell formation and the healthy functioning of the nervous system.
It is naturally found mainly in animal-derived foods, including meat, fish, eggs and dairy products. People following a vegan diet therefore need a reliable source from fortified foods or an appropriate supplement.
Vitamin B12 is not an instant energy booster. A supplement is most likely to make a noticeable difference when a low intake or deficiency is contributing to symptoms.
What is vitamin B12?
Vitamin B12 is a water-soluble B vitamin also known as cobalamin.
It is one of eight recognised B vitamins and is involved in helping the body make red blood cells, maintain the nervous system, release energy from food and use folate.
Vitamin B12 is stored in the body, so a low dietary intake may not cause immediate symptoms. NHS guidance notes that the body’s stores can last approximately two to five years without being replenished.
What is vitamin B12 good for?
Authorised health claims used in Great Britain state that 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 claims may only be used commercially when a food or supplement contains enough vitamin B12 to meet the relevant conditions. They do not mean that vitamin B12 can prevent, treat or cure a medical condition.
Vitamin B12 and normal energy metabolism
Vitamin B12 helps the body release energy from food and contributes to normal energy-yielding metabolism.
This does not mean that a B12 tablet, capsule or liquid works like caffeine. Vitamin B12 does not contain calories and should not be expected to create an immediate burst of energy.
Someone whose vitamin B12 intake is already adequate may notice no change after taking an additional supplement.
When low vitamin B12 is contributing to tiredness or a lack of energy, appropriate treatment or supplementation may help as the deficiency is corrected. However, tiredness can have many causes and should not automatically be attributed to vitamin B12.
Does vitamin B12 help with tiredness?
Vitamin B12 contributes to the reduction of tiredness and fatigue when a qualifying product provides the required amount.
However, this authorised nutritional claim does not mean that vitamin B12 will improve every type of tiredness.
Vitamin B12 may be relevant when tiredness is linked to:
- A low dietary intake
- Vitamin B12 deficiency
- A condition that affects absorption
- A medicine that affects vitamin B12 levels
Tiredness caused by poor sleep, stress, another nutrient deficiency or an underlying medical condition may not improve with a B12 supplement.
Persistent or unexplained tiredness should be discussed with a GP rather than managed indefinitely through supplements.
Vitamin B12 and the nervous system
Vitamin B12 contributes to the normal functioning of the nervous system.
A deficiency may cause neurological symptoms such as pins and needles, numbness, muscle weakness, balance problems or changes in memory and judgement. Some symptoms can occur even when a person has not developed anaemia.
This is why suspected vitamin B12 deficiency should be properly assessed rather than diagnosed based only on tiredness.
The NHS advises seeking medical advice promptly because certain problems caused by prolonged vitamin B12 deficiency may become irreversible if the deficiency is not treated.
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 a lack of vitamin B12 causes the production of abnormally large red blood cells that do not function properly, this is known as vitamin B12 deficiency anaemia.
Possible symptoms can include:
- Extreme tiredness
- Lack of energy
- Muscle weakness
- Breathlessness
- Pins and needles
- A sore or red tongue
- Problems with memory or concentration
These symptoms can have several causes, so blood testing and medical assessment may be needed.
Does vitamin B12 support the immune system?
Vitamin B12 contributes to the normal function of the immune system when a product contains enough to qualify for the authorised claim.
This does not mean that taking large amounts of B12 prevents infections or provides an “immune boost”.
A supplement should be used to help meet nutritional requirements rather than as a substitute for a balanced diet, sleep, vaccination or medical care.
Vitamin B12 and psychological function
Vitamin B12 contributes to normal psychological function.
This is an authorised nutritional function, but it should not be interpreted as a claim that vitamin B12 treats depression, anxiety, dementia or another mental health condition.
Mood, concentration or memory changes may occur with vitamin B12 deficiency, but these symptoms have many possible causes and require appropriate assessment.
Which foods contain vitamin B12?
Good dietary sources of vitamin B12 include:
- Meat
- Fish
- Milk
- Cheese
- Eggs
- Some fortified breakfast cereals
- Fortified yeast extracts
- Certain fortified plant-based foods and drinks
The NHS advises that adults aged 19 to 64 need approximately 1.5 micrograms of vitamin B12 per day. People who regularly consume meat, fish or dairy products should usually be able to obtain enough through their diet.
The amount in fortified products varies, so check the nutritional information on the label.
Can vegans obtain vitamin B12 from food?
Vitamin B12 is not naturally found in fruit, vegetables or grains. Vegans therefore need a reliable source through fortified foods or an appropriate supplement.
Possible fortified sources include:
- Plant-based milk alternatives
- Breakfast cereals
- Nutritional yeast
- Yeast extracts
- Meat alternatives with added B12
Not every plant-based product is fortified. Check the label rather than assuming that a food provides vitamin B12.
People who consistently find it difficult to obtain sufficient B12 through their diet may require ongoing supplementation. NHS guidance notes that some people following vegan diets may need vitamin B12 tablets for life.
Who may need to pay particular attention to vitamin B12?
People following vegan diets
Vegans are at greater risk of low dietary intake when they do not regularly consume fortified foods or a suitable supplement.
Vegetarians with limited eggs or dairy
Vegetarians who eat eggs and dairy products may obtain enough B12, but intake can be lower when these foods are rarely consumed.
Older adults
The ability to absorb vitamin B12 from food can decrease in some older adults. Vitamin B12 deficiency is also more common in older age groups.
People with pernicious anaemia
Pernicious anaemia is the most common cause of vitamin B12 deficiency in the UK. It prevents the body from producing enough intrinsic factor, a protein needed to absorb vitamin B12 effectively.
This requires medical treatment rather than reliance on an ordinary food supplement.
People with digestive conditions
Conditions affecting the stomach or intestines may reduce vitamin B12 absorption. These can include Crohn’s disease and conditions that affect the part of the gut where B12 is absorbed.
People who have had stomach or bowel surgery
Operations that remove part of the stomach or digestive system can affect vitamin B12 absorption and may require long-term monitoring or treatment.
People taking certain medicines
Some medicines can reduce vitamin B12 levels or absorption. NHS guidance identifies proton pump inhibitors and metformin among the medicines that may affect B12.
Do not stop prescribed medication. Ask a GP or pharmacist whether monitoring is appropriate.
What are the signs of vitamin B12 deficiency?
Possible symptoms include:
- Extreme tiredness
- Lack of energy
- Pins and needles
- Muscle weakness
- A sore or red tongue
- Mouth ulcers
- Changes in vision
- Problems with memory or understanding
- Psychological or mood changes
Some neurological symptoms can occur without anaemia. The NHS recommends seeing a GP when you think you may have a vitamin B12 or folate deficiency, as diagnosis usually involves symptoms and blood-test results.
Do not use a supplement to delay seeking advice about persistent numbness, weakness, balance problems or cognitive changes.
Is vitamin B12 the same as vitamin B complex?
No.
A standalone vitamin B12 supplement contains one specific B vitamin. A vitamin B complex usually contains several or all eight B vitamins.
A standalone B12 supplement may suit someone who:
- Follows a vegan diet
- Has a specifically low B12 intake
- Wants B12 without additional B vitamins
- Has been advised to use B12 by a healthcare professional
- Wants to avoid adding more vitamin B6 from a B-complex product
A vitamin B complex may suit someone who:
- Wants several B vitamins in one product
- Prefers broad B-vitamin nutritional support
- Has checked that the quantities are appropriate
- Does not need to target vitamin B12 alone
A B complex should not replace prescribed treatment for vitamin B12 deficiency.
What forms of vitamin B12 are used in supplements?
Common forms include:
- Cyanocobalamin
- Methylcobalamin
- Adenosylcobalamin
- Hydroxocobalamin
Cyanocobalamin is commonly used in food supplements. Methylcobalamin is also widely marketed, often at a higher price.
Current evidence does not show that vitamin B12 absorption from supplements consistently differs according to the form used. The overall product, serving, reason for supplementation and individual ability to absorb B12 are more important than marketing language around one particular form.
Which vitamin B12 format is best?
Vitamin B12 is available in formats including:
- Capsules
- Tablets
- Liquid drops
- Oral sprays
- Chewable tablets
- Lozenges
- Sublingual products
No one format is automatically best for everyone.
Evidence reviewed by the US National Institutes of Health suggests no clear difference in effectiveness between oral and sublingual vitamin B12 formats.
Choose a product based on:
- The amount of vitamin B12 per serving
- Clear directions
- Ease of use
- Dietary suitability
- Added ingredients
- Your reason for supplementation
- Advice from a healthcare professional where relevant
Are higher amounts of vitamin B12 better?
Not necessarily.
Standalone vitamin B12 supplements frequently contain much more than the daily dietary requirement because only a proportion of a large oral serving is absorbed. This does not mean that everyone needs a high-strength product.
The NHS states that taking 2mg or less per day of vitamin B12 from supplements is unlikely to cause harm, while also advising against taking more than needed.
Follow the directions on the product rather than automatically choosing the highest number available.
Does vitamin B12 give you instant energy?
No.
Vitamin B12 contributes to normal energy metabolism, but it is not a stimulant. Someone with an adequate intake may not feel any immediate difference after taking it.
People receiving appropriate treatment for a vitamin B12 deficiency may experience an improvement in deficiency-related tiredness over time. This should not be turned into a promise that an ordinary B12 supplement provides instant or all-day energy.
How long does vitamin B12 take to work?
There is no universal timeframe.
The result depends on:
- Whether a deficiency is present
- The cause of the deficiency
- The severity of the deficiency
- Whether absorption is impaired
- The treatment or supplement being used
- Whether neurological symptoms are present
- Whether tiredness has another cause
Diagnosed vitamin B12 deficiency may require tablets or injections and follow-up blood tests. NHS treatment guidance explains that the treatment plan depends on whether the cause is dietary and whether neurological symptoms are present.
An ordinary food supplement should not be presented as equivalent to medical treatment.
Can everyone benefit from taking vitamin B12?
Not everyone needs a standalone B12 supplement.
Someone who regularly eats meat, fish, eggs and dairy products may already obtain enough through their diet. Someone following a vegan diet or with limited dietary sources may have a clearer nutritional reason to consider supplementation.
A supplement may also be appropriate when recommended by a healthcare professional.
Taking extra vitamin B12 does not necessarily create additional energy or wellbeing when your intake and B12 status are already adequate.
What should you check before buying vitamin B12?
Amount per serving
Vitamin B12 is normally listed in micrograms, shown as µg or mcg.
Do not confuse micrograms with milligrams.
Form of vitamin B12
Check whether the product uses cyanocobalamin, methylcobalamin or another form, but do not assume the most expensive form is automatically superior.
Full serving size
Check whether the stated amount is provided by:
- One capsule
- Several drops
- A measured spray
- One or more tablets
Additional ingredients
Some products contain several B vitamins, vitamin C, sweeteners, flavourings or herbal ingredients.
Dietary suitability
Check whether the full product—not only the active vitamin—is confirmed as suitable for vegetarians or vegans.
Clear labelling
The product should display:
- Ingredients
- Recommended serving
- Warnings
- Storage instructions
- Responsible business details
- Best-before information
When should you speak to a GP?
Seek medical advice when you experience:
- Persistent or unexplained tiredness
- Pins and needles
- Numbness
- Muscle weakness
- Balance problems
- Changes in memory or concentration
- A sore or red tongue
- Vision changes
- Symptoms that are becoming worse
Vitamin B12 deficiency can often be treated, but early diagnosis is important because some nervous-system complications may become permanent.
Frequently asked questions
What is the main benefit of vitamin B12?
Vitamin B12 supports several normal functions, including energy metabolism, red blood cell formation and nervous-system function. It also contributes to reducing tiredness and fatigue when a product meets the conditions for that authorised claim.
Does vitamin B12 help you feel less tired?
It may help when low B12 intake or deficiency is contributing to tiredness. It may not make a noticeable difference when tiredness has another cause.
Is vitamin B12 good for vegans?
Vitamin B12 is particularly important for vegans because it is not naturally present in most plant foods. Reliable fortified foods or an appropriate supplement are therefore needed.
What foods contain the most vitamin B12?
Vitamin B12 is found in animal-derived foods such as meat, fish, eggs and dairy products. Some breakfast cereals, plant-based drinks and nutritional yeasts are fortified with it.
Can vitamin B12 improve concentration?
Vitamin B12 contributes to normal psychological and nervous-system function. However, it should not be promoted as a treatment for concentration or memory problems. Changes in cognition may need medical assessment.
Can vitamin B12 be taken every day?
Many B12 supplements are designed for daily use. Follow the label or the instructions provided by your healthcare professional.
Is vitamin B12 better than a B complex?
Neither is automatically better. B12 provides one targeted vitamin, while a B complex provides several B vitamins.
Can I take vitamin B12 with vitamin B complex?
You may be able to, but the B complex probably already contains B12. Check the total daily amount and whether the additional product is necessary.
Is methylcobalamin better than cyanocobalamin?
Current evidence does not establish that absorption rates consistently differ between the forms used in supplements. Compare the complete product rather than relying only on the form name.
Can vitamin B12 deficiency be self-diagnosed?
No. Symptoms overlap with several other conditions. A GP may use symptoms and blood-test results to investigate a possible deficiency.
Final answer
Vitamin B12 is good for supporting normal energy metabolism, nervous-system function, psychological function, red blood cell formation and the reduction of tiredness and fatigue.
It is naturally found mainly in meat, fish, eggs and dairy products. People following vegan diets need a dependable source from fortified foods or an appropriate supplement.
A vitamin B12 supplement is most relevant when dietary intake is low or a healthcare professional has recommended it. It should not be expected to provide instant energy when you already obtain enough.
Persistent tiredness, pins and needles, weakness or memory changes should be investigated rather than managed solely with supplements.