Does a Vitamin B12 overdose exist?

Is an overdose of vitamin B12 even possible?

Yes, an overdose can indeed occur in rare cases. However, not through food, but only through supplementation. Side effects can include dizziness, nausea, skin rashes, acne or diarrhea.

It is generally assumed that vitamin B12 also has a storage limit and that if this is exceeded, the excess is simply excreted. Exceptions to this are certain diseases such as hepatitis or leukemia, because in these cases the body can no longer excrete the excess B12. Or in older hospitalized people with chronic kidney disease, mortality can increase due to high B12 levels. [1]

Symptoms of a vitamin B12 overdose

It is difficult to say whether an overdose actually exists, as some symptoms can occur even with low doses of vitamin B12. For example

• Skin rashes or acne: This is one of the known symptoms, although vitamin B6 can also be a trigger - or if both B6 and B12 are taken, a slight intolerance may occur. But in any case, it does seem that skin sensitivity can be affected and lead to skin reactions such as pimples. [2]
• Dizziness and nausea: Higher doses of vitamin B12, as administered in the form of injections in the event of a deficiency, can temporarily overload the metabolism, the circulatory system or the reaction of the nervous system. However, this usually subsides quickly.

But what exactly is vitamin B12?

Vitamin B12 consists of various chemical compounds, the cobalamins. These are produced by bacteria. Fermented foods such as raw sauerkraut also contain small traces of vitamin B12. However, B12 can only be found in sufficient quantities in animal products.

Vitamin B12 is a water-soluble vitamin. This means that it can be more easily absorbed and transported by the body. Only a certain proportion of water-soluble vitamins is absorbed by the body, the rest is excreted in the urine. The body usually absorbs as much as it needs, with B12 the situation is somewhat different. The proportion that is actually absorbed depends on the amount of the vitamin and the body's capacity. At low doses, the body can absorb a larger percentage, whereas at higher doses, absorption is usually reduced and the excess is excreted.

Fat-soluble vitamins (A, D, E, K), on the other hand, need fat in order to be absorbed from the small intestine and taken up together with fats via the intestinal wall and then transported through the lymph into the blood with the help of lipoproteins. In contrast to water-soluble vitamins, excess fat-soluble vitamins are not excreted in the urine, but can be stored in fatty tissue and the liver.

Vitamin B12 has the same property as fat-soluble vitamins, namely that it can be stored in the body for several years. This is because it is bound to special transport and storage proteins in the body, which inhibit rapid breakdown and enable it to be stored in the liver. In addition, there is another special feature: part of the consumption and excretion of B12 is recycled, i.e. reabsorbed by the intestine and “recycled” via a special cycle.

I assume that this is due to evolutionary reasons, as vitamin B12 is involved in processes that are essential for survival, but can only be inadequately absorbed through food under certain circumstances. If the supply of meat was scarce in cave times, those who had sufficient vitamin B12 reserves stored in their liver had an advantage.

What does vitamin B12 do?

1. Formation of red blood cells

   The red blood cells ensure the transportation of oxygen in the body. Sufficient B12 helps to ensure that enough oxygen is transported and that the organs are optimally supplied with energy. A B12 deficiency can lead to a reduced number of red blood cells and thus to anemia.

2. Supporting the nervous system

   Our nerve fibers are surrounded by a protective sheath, the myelin sheath. This enables the rapid transmission of nerve impulses. A B12 deficiency can damage these myelin sheaths, which leads to reduced nerve function. A long-term deficiency can lead to irreversible nerve damage.

3. DNA synthesis

   Vitamin B12 is involved in DNA synthesis - a deficiency can disrupt cell division, which can inhibit the production of blood cells. This has serious consequences for cells with a high division rate, such as red blood cells or immune cells, as it can lead to developmental disorders and a weak immune system.

4. Mood and cognitive functions

   A lack of B12 can be associated with depression, cognitive disorders and memory problems. Some studies suggest that low levels of vitamin B12 may increase the risk of neurodegenerative diseases such as Alzheimer's, especially in older adults [3,4].

   The importance of vitamin B12 for the body can be seen in its many functions. It is essential for oxygen supply, cell division, the nervous system, metabolism, the immune system and mental health.

5. Breakdown of homocysteine

   Together with B6 and B9 (folic acid), B12 is able to break down homocysteine. If there is a deficiency of B12, among other things, homocysteine continues to rise or cannot be broken down properly, which can lead to damage to the blood vessel walls.

Reasons for vitamin B12 deficiency

In contrast to an overdose, a B12 deficiency is very common. Depending on diet, age and state of health. Below are the most important groups that may have an increased need:

1. Vegan diet

   B12 is mainly found in animal products such as meat, fish and eggs. If you go without it completely, you must either supplement or consume foods with fortified B12. Vegetarians can also be affected by a deficiency, which is why it is also worth having B12 tested regularly.

   People who have not been vegan for so long or who are taking medication usually still have enough vitamin B12, as the liver stores it for a long time. But at some point the store is empty and unfortunately this cannot be determined without regular testing.

2. Older people

   The body's ability to absorb B12 decreases with increasing age. This is because stomach acid production often decreases somewhat. However, stomach acid and intrinsic factor (a protein produced in the stomach) are necessary to release and absorb vitamin B12 from food.

3. Metformin

   Metformin, a drug prescribed for the treatment of diabetes, can interfere with B12 absorption in the small intestine. Diabetics must have their B12 levels tested regularly, as the risk of neuropathy (nerve damage) can increase with a vitamin B12 deficiency. [5]

4. Gastrointestinal diseases or stomach reduction

   In gastrointestinal diseases such as Crohn's disease or coeliac disease, the intestinal mucosa can be damaged. This reduces absorption.

   People who have undergone a stomach reduction can also have deficiencies, as the production of intrinsic factor is reduced.

5. Genetic variations

   People with certain genetic mutations, such as in the genes MTHFR or TCN2 (transcobalamin II gene), are less efficient at processing and storing vitamin B12.

6. Pregnancy and breastfeeding

   The vitamin B12 requirement is increased during pregnancy and breastfeeding, as the vitamin is important for the baby's development. Women who are vegan or vegetarian during these phases or who already have a low vitamin B12 level can therefore quickly develop a deficiency, which can affect not only their own health but also that of their baby. However, these women usually receive good medical care and are regularly checked for deficiencies.

7. Alcohol abuse

   Alcohol in high quantities can impair both the absorption and storage of vitamin B12, as the liver is often affected.

8. Liver or kidney disease

   Vitamin B12 is stored in the liver. A diseased liver can find it difficult to build up or maintain sufficient B12 stores.

   In chronic kidney disease, vitamin B12 absorption and excretion may be impaired.

What is the recommended daily intake of vitamin B12?

The Swiss Federal Food Safety and Veterinary Office FSVO recommends the following in the table Swiss reference values for nutrient intake:

• for adults a daily intake of 4 micrograms (µg)
• for pregnant women 4.5 µg
• 5.5 µg for breastfeeding women

In principle, this can be easily achieved through the diet, provided that animal products are consumed.

Food supplements are recommended if there is an increased requirement. These have a much higher value, from around 220 µg to high-dose supplements of 2000 µg.

Active and passive absorption of B12

Vitamin B12 can be absorbed in two ways. In active absorption, B12 binds to a protein, the intrinsic factor, in the stomach. This in turn can bind to specific receptors in the small intestine to enable the absorption of B12. Unfortunately, this only works in small quantities. This means that with a normal meal, 1.5 µg can be absorbed during a meal. This means that you would have to eat several meals containing B12 throughout the day in order to reach a daily dose of 4 µg or more.

The second way is so-called passive absorption. Here, B12 passes directly through the intestinal wall into the blood, but only about 1% at high doses. This means that a dosage of 1000 µg or more is needed to ensure that a sufficient amount enters the body.

Have B12 levels tested

In order to be able to determine a deficiency, it definitely makes sense to have your vitamin B12 level tested.

The 10 foods richest in vitamin B12

You should eat these foods regularly. The B12 content is given per 100g.

• Beef liver: 60-80 µg (by the way, this is also the best source of vitamin A)
• Oysters and mussels: 20-30 µg
• Fish - mackerel: 19 µg, trout: 7.5 µg, tuna: 5 µg, salmon: 3-5 µg
• Beef: 2-2.5 µg
• Cheese: Emmental approx. 2.8-3.1 µg, Sbrinz approx. 2.6-3 µg, Gruyère approx. 1.5-2 µg, Feta 1-1.8 µg
• Eggs (2): approx. 1.2-1.5 µg
• Chicken: 0.3-0.5
• Milk: 0.4-0.5 µg
• Plant-based milk alternatives: 0.5-1.5 µg (depending on the manufacturer)
• Greek yoghurt: 0.5 µg, low-fat quark: 0.3-0.4 µg