Vitamin B12: Who Needs It and How Much?

Vitamin B12 is one of the few nutrients that almost every plant-based guide mentions, and with Veganuary approaching, interest always rises in late autumn. But B12 is not only a vegan topic. Your needs, your absorption and your diet all change over the years, so it is worth understanding what this vitamin does and who is more likely to fall short.

What vitamin B12 does

Vitamin B12 (cobalamin) is a water-soluble vitamin your body needs in small but steady amounts. The authorised health claims in Great Britain set out its main roles:

• Vitamin B12 contributes to normal energy-yielding metabolism.
• Vitamin B12 contributes to the reduction of tiredness and fatigue.
• Vitamin B12 contributes to normal red blood cell formation.
• Vitamin B12 contributes to normal functioning of the nervous system.
• Vitamin B12 contributes to normal psychological function.
• Vitamin B12 contributes to the normal function of the immune system.
• Vitamin B12 has a role in the process of cell division.

Unlike most vitamins, B12 is stored in the liver, often for several years. That is why a shortfall can develop slowly and quietly long after a change in diet.

How much B12 do you need?

The UK reference nutrient intake for adults is 1.5 micrograms (µg) a day. Other authorities set higher figures: the United States uses 2.4 µg for adults, and the European Food Safety Authority sets an adequate intake of 4 µg. The differences reflect different methods rather than disagreement about B12's importance, but they explain why many supplements contain far more than 1.5 µg.

Why supplements are often high-strength

Your body absorbs B12 through two routes. A specialised route, which depends on a protein made in the stomach called intrinsic factor, absorbs only around 1.5 to 2 µg at a time. A second, passive route absorbs roughly 1% of any larger dose. This is why a once-daily 1,000 µg tablet is a common choice: the small fraction absorbed passively still adds up to a meaningful amount.

Who is more likely to fall short?

Vegans and people moving towards plant-based eating

B12 is found naturally in animal foods, such as meat, fish, eggs and dairy. Unfortified plant foods do not provide a reliable source. Cambridge University Hospitals' dietetic team advises anyone moving to a vegan diet to take a B12 supplement and to rely on fortified foods rather than hoping to get enough by chance. Seaweed, spirulina and fermented foods are not reliable sources.

Vegetarians

Eggs and dairy provide some B12, but intakes can be modest, especially if you eat them only occasionally. Note that B12 from eggs is less well absorbed than from other animal foods.

Older adults

Stomach acid production tends to fall with age, which makes it harder to release B12 from food. Supplements and fortified foods contain "free" B12 that does not need stomach acid to be released, which is why they are often suggested for people over 50.

People taking certain medicines

Some long-term medicines, including metformin and acid-reducing tablets such as proton pump inhibitors, can affect B12 absorption. If this applies to you, speak to your GP or pharmacist rather than self-diagnosing.

Food sources of vitamin B12

• Meat, especially beef and liver
• Fish such as salmon, sardines and tuna, plus shellfish
• Milk, yoghurt and cheese
• Eggs
• Fortified breakfast cereals, plant drinks and yeast extract (check the label)
• Fortified nutritional yeast flakes

Choosing a B12 supplement

If you follow a vegan diet, eat few animal foods, or are over 50 and want peace of mind, a daily B12 supplement is a simple, low-cost habit. Check three things: the amount per tablet, whether it is suitable for vegans, and how many days' supply the pot provides.

If you would rather cover the full B group in one tablet, a B complex is an alternative. Thiamin, riboflavin, niacin, vitamin B6 and B12 all contribute to normal energy-yielding metabolism, and biotin contributes to the maintenance of normal hair and normal skin.

Signs it is worth getting checked

Low B12 can cause tiredness, pins and needles, a sore tongue or problems with memory and mood. These symptoms have many possible causes, so do not guess. If you notice them, ask your GP for a blood test. Taking a high-dose supplement before a test can mask results, so mention any supplements you take.

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Frequently asked questions

How much vitamin B12 should I take a day?

The UK reference intake is 1.5 µg a day for adults. Because absorption from larger doses is limited, many people choose a daily tablet providing far more. Follow the label dose and speak to a health professional if you have been diagnosed with a deficiency.

Can you take too much B12?

B12 has very low toxicity and the excess is generally excreted. The UK Expert Group on Vitamins and Minerals considered 2,000 µg a day from supplements unlikely to cause harm.

Is B12 suitable for vegans?

Most B12 in supplements is made by bacterial fermentation, so many B12 tablets are vegan. Check the label for vegan certification and the tablet ingredients.

What is the best time of day to take B12?

There is no proven best time. Many people take it in the morning with breakfast so it becomes part of a routine.

Do I need B12 if I eat meat?

Most people who eat meat, fish, eggs and dairy regularly get enough from food. Older adults and people on certain medicines may still benefit from checking their levels.

Food supplements should not be used as a substitute for a varied, balanced diet and a healthy lifestyle.