Vitamin B12
Written by Martin Rhodes · Last reviewed August 2026
Why do I need vitamin B12?
Vitamin B12 is an essential vitamin that the body needs for several normal functions. It contributes to normal red blood cell formation, normal functioning of the nervous system, normal energy-yielding metabolism and normal psychological function.
B12 is naturally found in foods such as meat, fish, milk, cheese and eggs. Some foods are also fortified with vitamin B12. For most people, a varied and balanced diet can provide the B12 they need.
Adults need around 1.5 micrograms (µg) of vitamin B12 a day.
For some people, getting enough B12 can be more difficult because of their diet, certain health conditions, medicines or problems absorbing B12.
Cyanocobalamin vs methyl cobalamin: what's the difference?
Vitamin B12 is available in several forms. Two of the most commonly discussed in supplements are cyanocobalamin and methyl cobalamin.
Methyl cobalamin is one of the forms of B12 used by the body. Cyanocobalamin is a manufactured form of B12 that the body can convert into forms it can use.
This difference has led to a lot of discussion about which form is better. However, current evidence does not show that one form of supplemental B12 is generally better absorbed than another.
That doesn't mean the two forms are identical in every respect. They are different forms of B12 and are handled by the body through different steps.
For someone choosing a general B12 supplement, “methyl” doesn't automatically mean “better”.
What does “active B12” mean?
You may see terms such as “active B12” or “active form” used when describing some vitamin B12 supplements.
The term generally refers to forms of B12 that can participate directly in the body's biochemical processes. Methyl cobalamin and adenosyl cobalamin are forms of B12 used in these processes, while cyanocobalamin can be converted by the body into forms it can use.
This is one reason methyl cobalamin is often described as an “active” form.
However, “active” does not automatically mean “better”. Current evidence does not show that one form of supplemental B12 is generally better absorbed than another.
So when you see “active B12”, it's useful to understand what the term is referring to — but it shouldn't be treated as a simple measure of how good a supplement is.
How much vitamin B12 do I need?
Adults need around 1.5 micrograms (µg) of vitamin B12 each day.
That number can look surprisingly small when compared with the amounts found in many B12 supplements.
B12 supplements available to buy can range from around 10µg to 1,000µg, depending on the product.
So why can a supplement contain many times the amount we need each day?
One reason is that the amount of B12 absorbed becomes much smaller as the dose gets larger. This helps explain why some supplements contain much more B12 than the daily amount needed from the diet.
A higher number on the front of a bottle doesn't automatically mean a better product.
Why do B12 supplements contain such high doses?
If adults need around 1.5 micrograms of vitamin B12 a day, you might wonder why some supplements contain 100, 500 or even 1,000 micrograms.
Part of the answer is how B12 is absorbed.
At larger doses, only a small proportion of the B12 is absorbed. This helps explain why some supplements contain much more B12 than the amount we need from our diet.
So a 1,000 microgram supplement does not mean that the body absorbs 1,000 micrograms.
This helps explain why high-strength B12 supplements exist, but it doesn't mean that everyone needs a high-strength supplement.
Treatment for diagnosed B12 deficiency is different from choosing a general food supplement and can involve higher doses under professional guidance.
Is a higher dose of B12 better?
Not necessarily.
A higher amount of B12 in a supplement doesn't automatically make it a better choice.
The appropriate amount depends on the purpose of the supplement and the circumstances of the person taking it. High-dose B12 may also be used as part of medical treatment for diagnosed deficiency, where the appropriate treatment depends on the reason for the deficiency.
So when comparing B12 products, we don't simply look for the highest number on the label.
Who might need to pay particular attention to vitamin B12?
Not everyone has the same risk of vitamin B12 deficiency.
Some people may have a greater risk of deficiency because of their diet, certain health conditions, medicines or problems absorbing B12.
This can include people who:
follow a diet that excludes or is low in animal-source foods
have certain digestive or autoimmune conditions
have had some types of digestive surgery
take certain medicines, including metformin or proton pump inhibitors
have other risk factors identified in clinical guidance
Being in one of these groups doesn't automatically mean you have a B12 deficiency. The reason for low B12 can vary, and sometimes the issue is related to how the body absorbs B12 rather than simply how much is eaten.
If you think you may have a B12 deficiency, speak to a healthcare professional rather than assuming a supplement is the answer.
What are the signs of vitamin B12 deficiency?
Vitamin B12 deficiency can affect the body in different ways, and symptoms can develop gradually.
Possible symptoms include:
unusual or persistent tiredness
lack of energy
pins and needles
muscle weakness
a sore or red tongue
mouth ulcers
problems with vision
changes in memory, understanding or judgement
psychological changes
B12 deficiency can affect the nervous system as well as the blood, so feeling tired shouldn't automatically be taken as a sign that you need more B12.
If you think you may have a vitamin B12 deficiency, speak to a GP or other healthcare professional. Diagnosis takes account of symptoms and blood-test results, and further investigation may be needed to establish why B12 is low.
A B12 supplement isn't a substitute for finding out why you may be deficient.
Is vitamin B12 safe?
Vitamin B12 is generally well tolerated when taken as a supplement. However, this doesn't mean that taking more is automatically better.
The Food Standards Agency advises following the recommended dose on a supplement and seeking professional advice before taking high-dose supplements.
If you're pregnant or breastfeeding, have a medical condition or take regular prescribed medication, speak to a healthcare professional before taking a food supplement.
More isn't automatically better, and the recommended use on the product should always be followed.
When should I take B12?
For a general B12 supplement, there isn't a strong reason to suggest one particular time of day.
The important thing is to follow the recommended use for the product and take it consistently.
You'll sometimes see advice to take B12 in the morning or before food. However, for supplements bought from a shop or pharmacy, the simplest approach is to follow the instructions for the specific product you choose.
If you're taking B12 because you've been diagnosed with a deficiency, your healthcare professional may recommend a different dose or schedule depending on the reason for the deficiency.
Which B12 supplement should I choose?
There are plenty of B12 supplements to choose from, with different forms, amounts and ways of taking them.
We've been looking closely at the questions that matter when choosing a B12 supplement, and we're now doing the same work to decide what a This One Is B12 should look like.
We haven't chosen our B12 yet.
We're researching the form, amount, formulation and manufacturing standards before deciding whether it's a product we're happy to put our name to.
If you'd like to know what we decide, register your interest and we'll keep you in the loop.