How much B12 per day for a woman? The UK Department of Health and Social Care recommends 1.5 micrograms (µg) daily for adult women aged 19 and over, rising to 2.0 µg during breastfeeding. Vitamin B12 (cobalamin) is essential for red blood cell formation, neurological function, and DNA synthesis. Whilst the body stores several years' worth in the liver, regular intake remains vital to prevent deficiency. Women following plant-based diets, those over 50, and individuals with certain medical conditions may require higher intakes or supplementation to maintain optimal B12 status and prevent potentially irreversible neurological complications.

Recommended Daily B12 Intake for Women in the UK

Vitamin B12 (cobalamin) is an essential water-soluble vitamin that plays a crucial role in red blood cell formation, neurological function, and DNA synthesis. The UK Department of Health and Social Care recommends a Reference Nutrient Intake (RNI) of 1.5 micrograms (µg) per day for adult women aged 19 years and over.

This recommendation represents the amount sufficient to meet the needs of approximately 97.5% of the healthy female population. The body stores several years' worth of B12, mainly in the liver. However, regular dietary intake remains important to maintain optimal levels and prevent deficiency.

It is worth noting that the RNI is set at a level to prevent deficiency rather than to achieve optimal health in all circumstances. Some women may require higher intakes depending on individual factors such as age, dietary patterns, absorption capacity, and underlying health conditions. Older women, particularly those over 50 years, may have lower stomach acid (atrophic gastritis), reducing B12 absorption from food sources. Similarly, women following plant-based diets (vegetarian or vegan) are at increased risk of deficiency, as B12 is naturally found almost exclusively in animal-derived foods.

The body's ability to absorb B12 depends on intrinsic factor, a protein produced in the stomach, and adequate stomach acid. Conditions affecting the gastrointestinal tract or medications that reduce acid production may compromise absorption, potentially necessitating higher intakes or alternative supplementation routes.

B12 Requirements During Pregnancy and Breastfeeding

Pregnancy and lactation significantly influence a woman's nutritional requirements, including for vitamin B12. During pregnancy, the RNI remains 1.5 µg per day, the same as for non-pregnant women. However, many healthcare professionals recommend ensuring adequate intake through diet or supplementation, as maternal B12 status directly affects foetal development.

Low maternal B12 is associated with adverse neurodevelopmental outcomes in the developing foetus. Maternal deficiency during pregnancy has been associated with increased risk of neural tube defects, low birth weight, and developmental delays, though severe deficiency is required for these outcomes. The foetus relies entirely on maternal B12 stores and dietary intake, making adequate maternal status crucial throughout pregnancy.

For breastfeeding women, the RNI increases to 2.0 µg per day to account for B12 secretion in breast milk. Exclusively breastfed infants depend entirely on their mother's B12 status, and maternal deficiency can lead to infantile B12 deficiency, which may present with developmental regression, hypotonia, or failure to thrive. This is particularly important for women following plant-based diets, who should ensure adequate supplementation.

The NHS advises that women planning pregnancy or who are pregnant should consider taking a supplement containing B12, particularly if dietary intake may be insufficient. If taking a prenatal vitamin, check the label to ensure it provides at least the RNI for vitamin B12. Women with known deficiency may require higher therapeutic doses under medical supervision.

Signs You May Need More Vitamin B12

Vitamin B12 deficiency develops gradually, often over months to years, as the body depletes its hepatic stores. Early symptoms can be subtle and non-specific, making diagnosis challenging without clinical suspicion and appropriate testing. Recognising potential signs of deficiency is important for timely intervention and prevention of irreversible neurological damage.

Common symptoms of B12 deficiency include:

• Fatigue and weakness – often the earliest and most common complaint, resulting from impaired red blood cell production (megaloblastic anaemia)

• Neurological symptoms – paraesthesia (pins and needles), particularly in hands and feet; numbness; balance problems; and memory difficulties

• Glossitis and mouth ulcers – a sore, red tongue and recurrent oral ulceration

• Mood changes – depression, irritability, or cognitive difficulties including poor concentration

• Pale or jaundiced skin – due to anaemia and increased red blood cell breakdown

• Breathlessness and palpitations – secondary to anaemia reducing oxygen-carrying capacity

Neurological manifestations can occur even in the absence of anaemia and may include subacute combined degeneration of the spinal cord, affecting both motor and sensory pathways. If left untreated, these neurological changes can become permanent, emphasising the importance of early detection and treatment. Seek urgent medical advice for rapidly worsening numbness, gait disturbance, or new neurological deficits.

Certain groups are at higher risk of deficiency and should be particularly vigilant: women over 50 years (due to reduced stomach acid from atrophic gastritis); those following plant-based diets; individuals with pernicious anaemia (an autoimmune condition causing intrinsic factor deficiency); those with gastrointestinal disorders (Crohn's disease, coeliac disease); and women taking certain medications long-term, including proton pump inhibitors, H2-receptor antagonists, or metformin.

Food Sources and Supplements: Meeting Your B12 Needs

Dietary sources of vitamin B12 are almost exclusively animal-derived, as plants do not synthesise this vitamin. For women consuming animal products, meeting the RNI through diet alone is generally straightforward. Excellent food sources include:

• Meat and poultry – beef, lamb, and chicken liver are particularly rich sources (one 60g serving of liver provides approximately 40 µg)

• Fish and seafood – salmon, trout, tuna, and shellfish (particularly clams and mussels)

• Dairy products – milk, cheese, and yoghurt provide moderate amounts

• Eggs – one large egg contains approximately 0.6 µg

• Fortified foods – breakfast cereals, plant-based milk alternatives, and some yeast extracts and nutritional yeasts (check labels as not all are fortified)

For women following plant-based diets, fortified foods and supplementation are essential to prevent deficiency. Fortified breakfast cereals can provide 25–100% of the RNI per serving, whilst fortified plant milks typically contain 0.4–1.0 µg per 200ml serving. Fortified foods can meet needs if consumed in sufficient and regular amounts; always check labels for B12 content.

Vitamin B12 supplements are available in several forms: cyanocobalamin (the most stable and commonly used form in supplements), methylcobalamin, and hydroxocobalamin. For general supplementation, cyanocobalamin is effective and economical, typically available in doses ranging from 10 µg to 1000 µg. The body's intrinsic factor-mediated absorption is saturable (approximately 1.5–2 µg per dose), with larger oral doses relying on passive diffusion (approximately 1% absorption).

For prevention of deficiency in at-risk women, daily supplements of 10–25 µg are generally sufficient according to organisations like the British Dietetic Association and The Vegan Society. The NHS advises that taking up to 2000 µg daily is unlikely to cause harm, as excess B12 is excreted in urine. However, therapeutic treatment of established deficiency typically requires much higher doses or intramuscular injections under medical supervision.

When to Speak to Your GP About B12 Levels

Consulting your GP about vitamin B12 status is advisable if you experience symptoms suggestive of deficiency or belong to a high-risk group. Early medical assessment can prevent progression to irreversible neurological complications and ensure appropriate investigation and management.

You should contact your GP if you experience:

• Persistent fatigue or weakness not explained by other factors

• Neurological symptoms such as numbness, tingling, balance problems, or memory difficulties

• Unexplained mood changes, depression, or cognitive decline

• Symptoms of anaemia (pallor, breathlessness, palpitations)

• Sore tongue or recurrent mouth ulcers

• Any combination of the above symptoms

According to NICE Clinical Knowledge Summaries, initial investigation typically includes serum B12 measurement, full blood count (to assess for macrocytic anaemia), and blood film examination. Laboratory reference ranges and units (pmol/L or ng/L) vary locally. If B12 levels are borderline, additional tests such as holotranscobalamin, methylmalonic acid or homocysteine may help confirm deficiency. Where the cause is unclear, testing for pernicious anaemia (anti-intrinsic factor antibodies) may be appropriate.

Women following strict vegan diets should discuss B12 supplementation with their GP, particularly when planning pregnancy or if pregnant. Similarly, those with gastrointestinal conditions affecting absorption, autoimmune disorders, or taking long-term medications that may interfere with B12 absorption should request monitoring.

Treatment of confirmed deficiency depends on the underlying cause and severity. For dietary deficiency without neurological involvement, oral supplementation (typically cyanocobalamin 50–150 µg daily between meals) may be sufficient. However, deficiency due to pernicious anaemia or malabsorption requires intramuscular hydroxocobalamin injections, initially given on alternate days until no further improvement (up to 3 weeks) if neurological symptoms are present, then maintained at regular intervals (typically every two to three months for life in pernicious anaemia).

It is important not to start B12 supplementation before testing if deficiency is suspected, as this may interfere with diagnostic accuracy. If you have already commenced supplementation and are concerned about deficiency, inform your GP, as they may need to arrange additional investigations or consider a trial period off supplements before testing.

Frequently Asked Questions