Vitamin B12 for Runners: Why It Matters and How to Get Enough

Vitamin B12 is needed for healthy red blood cells, normal nervous system function and the production of DNA. These are important functions for everyone, but some of the effects of vitamin B12 deficiency, including tiredness, weakness and anaemia, are particularly relevant to runners. Most runners who eat a varied diet containing animal products should be able to obtain sufficient vitamin B12 through food.

However, runners following vegan diets need to pay particular attention to their intake because vitamin B12 is not naturally present in plant foods in reliable amounts. Some vegetarians, older adults and people with certain medical conditions or taking particular medicines can also be at greater risk of deficiency. So how important is vitamin B12 for runners, which foods provide it, and should runners consider taking a supplement?

What Is Vitamin B12?

Vitamin B12, also known as cobalamin, is a water-soluble vitamin that the body needs in relatively small quantities. It plays an important role in the formation of healthy red blood cells, maintaining the nervous system and making DNA.

Unlike many water-soluble vitamins, the body can store substantial amounts of vitamin B12, primarily in the liver. This means a deficiency caused by inadequate dietary intake can sometimes take years to become apparent rather than developing quickly.

Vitamin B12 occurs naturally mainly in animal-derived foods, including meat, fish, eggs and dairy products. Plant foods do not provide a reliable natural source, although many breakfast cereals, plant-based drinks, yeast extracts and other foods are fortified with B12.

Why Is Vitamin B12 Important For Runners?

One of B12's most relevant functions for runners is its involvement in the production of normal red blood cells. Red blood cells contain haemoglobin, which transports oxygen from the lungs around the body, including to working muscles.

A serious B12 deficiency can result in megaloblastic anaemia, in which the body produces abnormally large red blood cells that do not function normally. Anaemia can reduce the body's ability to transport oxygen effectively and may result in tiredness, weakness and reduced exercise capacity. Research examining vitamin and mineral status and physical performance has found that severe B12 and folate deficiency resulting in anaemia can reduce endurance performance.

B12 is also important for normal neurological function. That matters because the nervous system controls muscle movement, coordination and many of the processes involved in running. However, there is an important distinction between preventing deficiency and taking extra vitamin B12 in an attempt to improve running performance.

There is not good evidence that runners who already have adequate B12 status will become faster, have more energy or improve their endurance simply by consuming additional B12. Correcting a nutrient deficiency can be important, but taking progressively larger amounts of a nutrient you already obtain adequately does not necessarily provide an additional benefit.

Does Running Increase Your Vitamin B12 Requirement?

There is currently no established separate vitamin B12 recommendation specifically for runners. Although exercise can influence requirements for some micronutrients, research examining whether athletes have greater requirements for B12 remains limited.

Research into B vitamins and exercise has found some evidence that physical activity may increase requirements for certain B vitamins, but there is insufficient evidence to establish an increased requirement for vitamin B12. Runners therefore do not generally need to consume more B12 simply because they run.

What can matter is the runner's overall diet. Athletes who restrict their food intake, exclude major food groups or have very low energy availability have a greater chance of consuming inadequate amounts of individual micronutrients. The same applies to runners adopting diets that naturally contain little or no B12.

How Much Vitamin B12 Do Runners Need?

UK dietary guidance sets the Reference Nutrient Intake for vitamin B12 at 1.5 micrograms a day for people aged 15 and over. There is no higher official recommendation specifically for runners or other endurance athletes.

Recommendations vary somewhat between countries because different health authorities use different methods when setting nutrient reference values. This is one reason runners searching online may see different daily figures. Rather than trying to hit a precise number at every meal, the priority should be maintaining a reliable long-term source of B12.

For people eating animal products, this can normally be achieved through a varied diet. People following a vegan diet need sufficiently fortified foods, an appropriate B12 supplement or a combination of the two.

The Best Food Sources Of Vitamin B12

Fish, shellfish, meat, poultry, eggs, milk and other dairy products can all provide vitamin B12, although the amount varies considerably between foods. Fish and shellfish can be particularly rich sources, while milk, yoghurt and eggs can make useful contributions for runners who eat them.

For a runner eating an omnivorous diet, obtaining B12 does not usually require concentrating on one particular food. Eating a varied diet that regularly contains B12-rich foods will normally provide a mixture of sources.

Vegetarians who consume eggs and dairy also have natural sources available, although research indicates that B12 status can still be lower in vegetarians than in people who regularly eat meat and fish. Long-term vegetarians should therefore still be aware of their overall intake rather than assuming that eating some dairy products or eggs automatically guarantees sufficient B12.

Milk and yoghurt are good sources of vitamin B12.

Vitamin B12 For Vegan Runners

B12 deserves particular attention if you are a vegan runner. A well-planned vegan diet can support endurance training and performance, but vitamin B12 is one nutrient that cannot reliably be obtained from unfortified plant foods.

Research into nutrition for vegan athletes has identified vitamin B12 alongside nutrients such as iron, calcium and vitamin D as one of the micronutrients requiring particular attention. Vegan athletes can meet their nutritional requirements and perform successfully, but doing so requires appropriate planning.

Fortified plant-based drinks, some breakfast cereals, plant-based yoghurt alternatives and fortified yeast extracts can provide B12. The crucial word is fortified: products vary considerably, so check the nutritional information rather than assuming that every plant-based alternative contains B12.

For vegan runners, B12 therefore needs to be planned rather than left to chance. The British Dietetic Association recommends using reliable fortified foods or a B12 supplement.

Because the amount absorbed varies according to the dose, supplement doses are normally considerably higher than the 1.5 microgram daily UK reference intake. Check the nutritional information on fortified foods and follow appropriate professional or product guidance when choosing a supplement.

Signs Of Vitamin B12 Deficiency

Vitamin B12 deficiency can produce a wide range of symptoms, and several could easily be mistaken by a runner for the effects of heavy training, insufficient recovery or general fatigue.

Symptoms can include extreme tiredness, lack of energy, muscle weakness, pins and needles, a sore or red tongue, mouth ulcers and problems with memory or concentration.

Neurological symptoms can also include numbness and problems with balance or coordination. Importantly, some neurological symptoms can occur even in the absence of anaemia.

A runner experiencing persistent unexplained fatigue or a significant deterioration in running performance should therefore avoid assuming that the problem is simply a vitamin deficiency and self-treating it. Many different nutritional, medical and training-related issues can produce similar symptoms.

Who Is More At Risk Of Vitamin B12 Deficiency?

Diet is one potential cause of deficiency, but it is not the only one. Vegan runners who do not regularly consume fortified foods or supplements are an obvious higher-risk group, while some long-term vegetarians may also have low B12 status.

Absorption can also be a problem. Vitamin B12 from food has to go through several stages before it can be absorbed, and conditions affecting the stomach or the end of the small intestine can interfere with this process. Autoimmune gastritis can reduce the body's ability to absorb B12 and has historically been associated with pernicious anaemia.

People who have undergone certain types of gastrointestinal surgery may also have an increased risk, as can people with conditions affecting the part of the intestine where B12 is absorbed, including Crohn's disease.

Certain medicines are another consideration. Current NICE guidance identifies medicines including metformin and acid-suppressing drugs such as proton pump inhibitors and H2-receptor antagonists among potential risk factors for B12 deficiency. Older age can also increase the likelihood of problems absorbing B12 from food.

Vitamin B12, Iron And Anaemia In Runners

Iron deficiency receives considerable attention in running because of iron's role in haemoglobin and oxygen transport, but iron deficiency is not the only nutritional cause of anaemia.

Vitamin B12 and folate are both needed to produce normal red blood cells. A deficiency in either can cause megaloblastic anaemia, while iron deficiency typically produces a different form of anaemia. Symptoms such as tiredness, weakness and reduced exercise capacity can overlap, which is one reason diagnosis matters rather than guessing which nutrient might be responsible.

This is particularly important for runners because training itself produces fatigue. A poor run or a difficult training week does not mean you have iron or B12 deficiency, but persistent unexplained fatigue deserves investigation.

Read more about iron for runners here.

Should Runners Take A Vitamin B12 Supplement?

Most runners who regularly eat foods containing vitamin B12 and have no absorption problem will not need a B12 supplement specifically because they run. More B12 does not automatically mean more energy or better endurance.

The position is different for vegan runners. Because unfortified plant foods are not a dependable source of B12, a reliable strategy involving fortified foods, supplements or a combination of the two is essential.

Anyone who suspects that they are deficient should not rely solely on an over-the-counter supplement without considering why the deficiency has occurred. If poor absorption rather than inadequate food intake is responsible, the appropriate treatment may be different.

Read more about supplements for runners here.

Can You Take Too Much Vitamin B12?

Vitamin B12 has relatively low toxicity and no tolerable upper intake level has been established by some major health authorities because available evidence has not shown B12 to cause harm at the intakes assessed. This should not be interpreted as evidence that taking very large doses provides additional benefits.

High-dose B12 products can contain hundreds or even thousands of micrograms, which can look extraordinary compared with daily dietary requirements. These doses partly reflect the way B12 is absorbed rather than suggesting that the body needs hundreds of times the normal dietary intake.

For runners who already obtain enough B12, taking increasingly large doses is unlikely to provide an additional running benefit.

Can You Test Your Vitamin B12 Level?

Vitamin B12 deficiency can be investigated using blood tests alongside symptoms, medical history and other relevant information. NICE recommends either total B12 or active B12 as an initial diagnostic test in most circumstances, although interpreting B12 status is not always as straightforward as simply being above or below a single universal number.

If you have symptoms that could indicate B12 deficiency, seek medical advice rather than simply starting high-dose supplements. Blood tests can help establish whether B12 deficiency is present and further investigation may be needed to identify its cause.

When Should A Runner Seek Medical Advice?

Persistent fatigue, unusual weakness, pins and needles, numbness, balance problems or an unexplained decline in exercise capacity should not automatically be attributed to training. These symptoms have many possible causes and vitamin B12 deficiency is only one of them.

Early diagnosis matters particularly when neurological symptoms are present because untreated B12 deficiency can sometimes result in neurological problems that become difficult to reverse. Seeking medical advice is therefore important if you have persistent symptoms or believe you may be at increased risk of deficiency.

The Bottom Line For Runners

Vitamin B12 is essential for normal red blood cell formation and nervous system function, making an adequate intake important for runners as well as everyone else. A significant deficiency can cause fatigue, weakness, neurological symptoms and anaemia and can ultimately interfere with endurance performance.

There is no convincing reason, however, for a runner with adequate B12 status to take large additional amounts in the hope of becoming faster or more energetic. Most runners eating a varied diet containing animal foods should obtain enough naturally, while vegan runners need a dependable source from fortified foods, supplements or a combination of the two.

The important message is not that runners need extra B12, but that they need enough. If persistent fatigue or other symptoms suggest a possible deficiency, getting the cause properly investigated is far more useful than guessing and simply adding another supplement.