Vitamin B12: What It Is, What Role It Plays and How to Take It Properly

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Vitamin B12 is a water-soluble vitamin that your body needs to keep nerve cells and red blood cells healthy, and to make DNA. It's an essential vitamin from the B-complex group that the body can't produce on its own — so you need to get it through your diet or with the help of supplements.

Have you ever noticed how tired you feel during your period? Have you found that you're lacking energy and struggling to keep up with your usual daily pace? A 2011 study found that many women — particularly those with severe premenstrual syndrome — experience drowsiness and exhaustion during menstruation, along with a slowing of psychomotor function. Such states can have many causes, but a vitamin B12 deficiency may play a role in all of them. In this article, we explain the connection between this nutrient, your energy levels and possible anaemia.

What is vitamin B12? 

Let's start with the most obvious question about vitamin B12: what exactly is it?

Vitamin B12 is a water-soluble vitamin from the B-complex group. Because it contains the trace element cobalt, it's also known as cobalamin.

It's a vitamin that's indispensable for normal bodily function, which the body doesn't produce itself and which you can obtain either through your diet or through supplements. The forms most commonly used in supplements are cyanocobalamin and methylcobalamin. Both help to maintain adequate levels in the body.

Vitamin B12 is only needed in small amounts, yet it performs important functions for your health. Among the most significant are:

• Contributing to the normal formation of red blood cells and reducing the risk of anaemia
• Supporting the nervous system and maintaining the health of nerve cells
• Participating in DNA synthesis and energy production at a cellular level

The role of vitamin B12 in the body 

Vitamin B12 is involved in forming the myelin sheath — the protective layer around nerves that allows nerve impulses to travel efficiently. It supports the normal formation of red blood cells, plays a part in DNA synthesis and helps break down homocysteine, an amino acid which, at elevated levels, is associated with a higher risk of cardiovascular disease. Cobalamin also contributes to normal energy metabolism — which is why a deficiency can lead to fatigue and a lack of energy.

Why vitamin B12 matters particularly for women 

As a woman, you have several reasons to pay attention to your vitamin B12 intake — especially at certain stages of life. Optimal levels support your normal energy metabolism and the healthy functioning of your nervous system, which is reflected in balanced energy levels and overall well-being. A deficiency can upset this balance.

If you have heavy periods, these can increase your risk of anaemia — particularly if there's also a B12 or iron deficiency. During pregnancy and while breastfeeding, your vitamin B12 requirements increase in order to support the normal development of your baby's nervous system.

If you follow a vegetarian or vegan diet, you're more prone to B vitamin deficiency. The main natural sources of vitamin B12 are animal-based foods — without these, the likelihood of a deficiency rises.

Optimal levels support your normal energy metabolism and the healthy functioning of your nervous system, and have a significant influence on your energy levels and general well-being.

The benefits of vitamin B12 

From the formation of red blood cells and the functioning of the nervous system to the normal development of the foetus in pregnancy and supporting the body during menstruation — the benefits of vitamin B12 stem from the biological roles it fulfils in the body. It's involved in essential processes that affect both your physical health and your well-being.

Supports red blood cell formation and helps prevent anaemia 

Vitamin B12 is indispensable for the normal formation of red blood cells. Without it, the bone marrow produces red blood cells that are larger than normal and insufficiently developed, and which transport oxygen less efficiently. This condition is known as megaloblastic anaemia.

Unlike iron-deficiency anaemia, which is caused by a lack of iron and characterised by small red blood cells, anaemia due to vitamin B12 deficiency is often accompanied by neurological symptoms such as tingling, numbness or balance problems.

Counteracts fatigue and supports energy

Although vitamin B12 doesn't directly provide energy, it contributes to normal energy metabolism and helps the body convert carbohydrates, fats and proteins into usable energy.

With a vitamin B12 deficiency, insufficient production of red blood cells reduces the amount of oxygen reaching the tissues — which can lead to persistent fatigue, weakness and reduced stamina.

Supports the nervous system and good mood

Vitamin B12 is needed to form and maintain the myelin sheath, the protective covering of nerve fibres. Without it, nerves may transmit impulses more slowly or inefficiently — which can cause tingling in the hands and feet, numbness, balance problems or muscle weakness.

A severe and prolonged deficiency is also associated with difficulty concentrating, irritability, mood swings and, in some cases, depression.

Essential in pregnancy and while breastfeeding

During pregnancy, vitamin B12 is necessary for the normal development of the foetus's brain and nervous system, as well as for DNA synthesis during this phase of accelerated growth.

Maternal deficiency during pregnancy is associated with a higher risk of neural tube defects, foetal growth restriction and premature birth. During breastfeeding, vitamin B12 passes into breast milk — so an adequate intake is equally important for the mother and for the baby's development.

What's more, a recent study from 2025 links adequate vitamin B12 levels during pregnancy with a lower risk of postnatal depression.

Contributes to the health of hair, skin and nails

Vitamin B12 supports normal cell division, which is essential for rapidly regenerating tissues — skin, hair follicles, nails. A deficiency can contribute to increased hair loss, brittle nails or changes to the skin and mucous membranes.

If your vitamin B12 levels are normal, however, taking supplements won't further stimulate hair growth, nor will it visibly improve your skin.

Supports cognitive health and memory

The brain and nervous system rely on vitamin B12 for their normal functioning. Low levels can affect memory, attention and the speed at which you process information, particularly in older people.

While a deficiency must be corrected to prevent these symptoms from worsening, there is currently no evidence that supplementation improves cognitive performance in people who aren't deficient.

Vitamin B12 and the menstrual cycle: what's the connection? 

Hormonal changes, menstrual blood loss and the symptoms of premenstrual syndrome — particularly in its severe form — all generally contribute to a drop in energy levels, a phenomenon that thousands of women face month after month.

Vitamin B12 plays an important role in this process. Because it contributes to the formation of red blood cells and to normal energy metabolism, optimal levels can support your body during this time. A deficiency, on the other hand, can intensify fatigue and feelings of weakness — especially if anaemia is also present.

Vitamin B12 also contributes to the normal functioning of the nervous system. It's involved in the processes of serotonin synthesis, a neurotransmitter linked to mood regulation. While it isn't a treatment for premenstrual syndrome, optimal levels can support your well-being.

It's important to understand that heavy bleeding, or menorrhagia, doesn't usually cause vitamin B12 deficiency. It simply increases the risk of iron-deficiency anaemia, because heavy blood loss means you lose more iron — and consequently need to change your period products more frequently. However, iron deficiency and vitamin B12 deficiency can occur at the same time, and together they impair the normal formation of red blood cells and oxygen transport around the body. That's why a good B vitamin status can support the health of your blood.

While working to treat the anaemia associated with hypermenorrhoea, gynaecologists made the surprising discovery of a strong influence of vitamin B12 levels and the B vitamin complex. In a 2020 publication, they confirmed that vitamin B12 may help raise oestrogen levels, leading to a thickening of the uterine lining and potentially playing a role in the treatment of heavy menstrual bleeding.

On the other hand, a more recent study from 2021 indicates that vitamins B2 and B12 can lower homocysteine — a substance in the blood that, at high concentrations, is considered a risk marker for cardiovascular health. However, they don't appear to influence either the menstrual cycle or ovulation in premenopausal women. So they don't significantly alter how the ovarian cycle works, nor can they be considered an effective treatment for cycle disorders.

If you suffer from menorrhagia and also follow a vegetarian or vegan diet, you should pay particular attention to your vitamin B12 intake, because you face a double risk. On the one hand, low dietary intake increases your risk of vitamin B12 deficiency. On the other, menstrual losses increase your risk of iron deficiency. So listen to your body. If you feel tired and that tiredness persists from one cycle to the next, speak to your doctor and have tests carried out covering both your vitamin B12 levels and markers of iron status (ferritin and a full blood count).

Sources of vitamin B12 

Vitamin B12 occurs naturally almost exclusively in animal-based foods: meat, liver, oily fish, eggs and dairy products. It's produced by certain bacteria that typically accumulate in animal tissue — which is why plant-based sources are virtually non-existent, and why people following vegetarian and especially vegan diets have an increased risk of deficiency.

The table below shows the main sources of vitamin B12 according to Harvard Health:

Food                                                                  Portion                                              Vitamin B12 content

Clams                                                                   85 g                                               84 mcg

Fortified breakfast cereals                    (as per nutritional information)         6 mcg

Trout                                                                85 g                                                5.4 mcg

Salmon                                                               85 g                                               4.9 mcg

Tinned tuna                                                85 g                                                2.5 mcg

Fortified chocolate soya milk                (as per nutritional information)       1.7 mcg

Beef                                                                    85 g                                                 1.5 mcg

Low-fat Greek yoghurt                              170 g                                                1.3 mcg

Swiss cheese                                               85 g                                               0.9 mcg

Ham                                                                   One slice                                           0.6 mcg

Egg                                                                    1 large                                              0.6 mcg

Roast chicken breast                                  85 g                                               0.3 mcg

Vitamin B12 deficiency: causes and symptoms

In the UK, an estimated 6% of people under 60 and around 20% of those aged 60 and over have vitamin B12 deficiency (estimates cited in NHS primary-care guidance). Testing is primarily indicated for people with risk factors and typical symptoms; diagnosis is based on serum B12 levels.

On the other hand, very high and persistently elevated B12 levels can be associated with serious conditions such as certain cancers or an increased cardiovascular risk — so supplementation should only be undertaken on medical advice.

Causes and risk factors 

Vitamin B12 deficiency occurs when the body doesn't get enough through the diet or can't absorb it adequately (malabsorption), and according to medical publications can lead to haematological and neurological symptoms. Those most susceptible to such deficiencies include:

• People following a vegan or strictly vegetarian diet without supplementation
• Older adults, in whom absorption naturally declines
• People with digestive conditions such as Crohn's disease, coeliac disease or atrophic gastritis
• Patients taking medicines such as metformin (used in diabetes), proton pump inhibitors or other treatments that reduce stomach acid
• Patients who have undergone bariatric procedures or other surgery on the stomach and intestines, which can impair the absorption of vitamin B12 and lead to deficiency

Symptoms

Vitamin B12 deficiency usually develops slowly, as the body can build up reserves lasting several years. The first signs — as a result of anaemia — are persistent fatigue, general weakness, pallor, dizziness and breathlessness on exertion.

If the deficiency worsens, further symptoms of vitamin B12 deficiency may appear:

• Tingling or numbness in the hands and feet
• Balance problems
• Difficulties with concentration and memory
• Irritability or low mood

A retrospective clinical study from 2019 involving 38 children aged 0 to 18 with vitamin B12 deficiency confirmed symptoms such as fainting, dizziness, seizures, reduced muscle tone, developmental delay, tremor, ataxia, tingling and paraesthesia, blurred vision, fatigue and difficulty concentrating — all linked to the vitamin B12 deficiency.

If you notice such symptoms, it's important to see a doctor as soon as possible for further investigation. This may include blood tests for vitamin B12, a full blood count and, depending on the situation, other deficiency markers.

How is vitamin B12 taken? 

Wondering how to take vitamin B12? Cobalamin is available as a supplement in various forms, suited to different needs and the body's ability to absorb it.

Oral forms — tablets, sublingual tablets, drops or sprays — can be taken with or without food; absorption generally depends on the form of the vitamin and the state of your digestive system. In cases of severe deficiency, for instance in patients who have had bariatric surgery or who have certain digestive conditions causing severe malabsorption, a doctor may recommend vitamin B12 by injection, as this bypasses the digestive tract and ensures direct absorption.

Requirements vary according to age and physiological circumstances. According to the NIH, the following daily intake guidelines apply:

• 0–6 months: 0.4 mcg
• 7–12 months: 0.5 mcg
• Children, 1–3 years: 0.9 mcg
• Children, 4–8 years: 1.2 mcg
• Children, 9–13 years: 1.8 mcg
• Adolescents, 14–18 years: 2.4 mcg
• Adults: 2.4 mcg
• Pregnant adolescents and women: 2.6 mcg
• Breastfeeding adolescents and women: 2.8 mcg

It's precisely to meet these increased requirements that supplementation is generally recommended for vegans and vegetarians, pregnant and breastfeeding women, older people, and anyone with a deficiency confirmed by laboratory results.

Form                                                                    Use                                                                                                    Suitable for:

Oral capsules                                   Taken daily or according to the recommended regimen                   People without absorption problems

Sublingual                                          Dissolves under the tongue, partly absorbed directly       People with slightly reduced absorption or those who prefer a fast-acting form

Drops or oral spray                          Taken orally in small, easily adjustable doses                                      Children and people who have difficulty swallowing

Intramuscular injections        Only on medical advice, administered regularly by a healthcare professional      Severe deficiency, malabsorption, gastric/bariatric surgery

In principle, vitamin B12 is water-soluble, and excess amounts are excreted in the urine. Even so, supplementation should be informed and responsible — based on laboratory results and medical advice.

Normal values and testing for vitamin B12 

Vitamin B12 levels are measured via a venous blood test, usually in the morning on an empty stomach, depending on the requirements of the laboratory or your doctor. Testing makes sense if you have symptoms suggesting a deficiency, if you have known risk factors, or if the effectiveness of supplementation needs to be checked.

According to UCSF Health, the range considered normal for vitamin B12 in the blood is 160–950 pg/ml, although values may vary depending on the laboratory and clinical context. Results should therefore not be viewed in isolation; vitamin B12 levels are assessed alongside symptoms and sometimes other laboratory values such as a full blood count or ferritin.

If a deficiency is suspected, it's important to discuss the assessment and treatment decisions with your doctor.

Frequently asked questions

Got questions about vitamin B12? We have the answers. Here are some of the most common questions about vitamin B12 deficiency, taking supplements and how long it takes to get back to optimal levels.

What are the signs of vitamin B12 deficiency?

Persistent fatigue, pallor, dizziness and muscle weakness can be signs of vitamin B12 deficiency, caused by a reduced number of red blood cells. In severe cases, tingling in the hands and feet, difficulty concentrating, memory problems and mood changes can occur.

How is vitamin B12 taken — orally or by injection?

Vitamin B12 is most commonly taken orally, in the form of tablets, capsules, drops or spray. Doctors only recommend the injectable form in cases of severe deficiency or malabsorption, as it bypasses the digestive system and ensures direct absorption.

Can a vitamin B12 deficiency make fatigue worse during menstruation?

Yes, a vitamin B12 deficiency can intensify the tiredness that's typical during menstruation, as cobalamin contributes to the formation of red blood cells and to oxygen transport. Combined with blood loss during your period, low levels can lead to greater weakness.

How long does it take to restore B12 levels?

How long it takes to correct a vitamin B12 deficiency depends on its severity and the form taken. In mild cases, levels can improve within a few weeks of oral supplementation. With severe deficiency or injections, symptoms may improve more quickly, although fully replenishing stores can take a few months.

Can I take vitamin B12 if I'm vegetarian or vegan?

Yes, people following a vegetarian or vegan diet can take vitamin B12 as a supplement. In these cases supplementation is in fact recommended to prevent deficiency. The dose and the most suitable form should always be determined according to individual needs and ideally on the basis of laboratory results.

Should vitamin B12 be taken in the morning or the evening?

Cobalamin can be taken either in the morning or in the evening — the effect is the same. Some people prefer to take it in the morning, as it's involved in energy metabolism and can support energy levels throughout the day. There's no strict rule, though: consistency matters more than the time of day.

Is too much vitamin B12 dangerous?

Vitamin B12 is water-soluble, so excess amounts are generally excreted in the urine, and toxicity is rare. Even so, long-term high-dose supplementation without medical indication isn't advisable, as it may mask other deficiencies or simply be unnecessary.

Conclusion

Vitamin B12 is essential in the body for supporting your energy levels, the formation of healthy red blood cells and the functioning of your nervous system. Optimal levels can make all the difference, particularly at times when you feel tired — including during menstruation. Depending on your needs and your doctor's advice, you can take vitamin B12 orally or by injection to support your body more consciously in everyday life.

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