What happens when you overdose on vitamin b12?

If you’re vegan or vegetarian, you’ve probably been told that you have an even higher risk of being deficient in certain nutrients, especially B12. One of the reasons for this is that B12 is only found in animal sources.

But even those who eat plenty of meat and eggs may be low in this essential nutrient. In fact, if you’ve been feeling tired, depressed, or just generally out of sorts, there’s a good chance your B12 levels are already sub-par.  

In the US, deficiency in most of the B vitamins is now very low (<1% of the population) due to the fact that these vitamins have been added to cereal grain products for decades.

But B12 remains the predominant B vitamin deficiency.

So, you just have to go out and take a supplement, right?

Well, yes and no. 

Taking B12 supplements is a great way to top up your B12 levels - but ONLY if you take the right one!

There’s a huge range of supplements on the market these days. Some are great, and some may be completely ineffective. Some may even be harmful. 

And just to make things even more confusing, there’s a lot of so-called information on the internet about what happens when you overdose on B12.

First things first: when you take the right B12, the risk of overdosing is almost non-existent. Let’s explain why. 

No matter what age you are - or how healthy you are - you need all eight B vitamins every day for your body to function properly. These vitamins are referred to as the B complex, and comprise of thiamine (B1), riboflavin (B2), niacin (B3), pantothenic acid (B5), vitamin B6, folate (B9) and vitamin B12. 

Each of the B complex vitamins shares certain cellular coenzyme functions and are often found in the same foods. 

The most important job of the B complex is in the catabolic process of generating energy within cells. For example, the active forms of thiamine, riboflavin, niacin, and pantothenic acid are particularly important as coenzymes in cellular energy production.

Thiamine, biotin and vitamin B12 also have special roles in the mitochondrial metabolism of glucose, fatty acids and amino acids, which are vital components of the citric acid cycle. Together, they help your body break down glucose (blood sugar) and create energy in the form of ATP molecules. Without ATP, your heart, brain, and other crucial organs would not be able to function.

It’s for this reason that being deficient in any one of the B vitamins can have severe consequences on your daily energy levels, brain function, cardiovascular function, and your mood. 

Like the other Bs, Vitamin B12 plays an important role in energy production, the formation of red blood cells, and the synthesis of fatty acids. It works closely alongside vitamin B9 (also called folate) to help make red blood cells which are required for carrying oxygen to all parts of your body.

But there are many reasons that set B12 apart from every other vitamin. 

Vitamin B12 is the only B vitamin that is not made by plants.

Vitamin B12 is referred to as cobalamin because it’s the only known vitamin that has the form of the metal “cobalt” and still reacts with humans, plants, and animals. Cobalt gives Vitamin B12 its natural red color.

While the other eight B vitamins are made by plants, B12 is made by bacteria in the gut of ruminant animals. Ruminants acquire vitamin B12, through a symbiotic relationship with the bacteria present in their stomachs. This is why humans can only source B12 from foods (such as fish, meat, poultry, eggs, milk products) or supplements.

Absorption of B12 is tricky

B12’s unique composition means it’s bound to the protein in food. For us humans, that means we need something called intrinsic factor in order to absorb and use B12 properly. Intrinsic factor is a glycoprotein made by the parietal cells lining the stomach. Our stomach releases hydrochloric acid during digestion, which then releases B12 from protein so it can combine with intrinsic factor. This makes it possible for B12 to be absorbed later on in the ileum of the small intestine.

A lack of intrinsic factor means impaired uptake of vitamin B12, which can result in a B12 deficiency.

B12 is crucial for reducing homocysteine

B12 works alongside folate and vitamin B6 to lower concentrations of homocysteine. Homocysteine is an amino acid that is an intermediate in the production of two other amino acids, methionine and cysteine. Although homocysteine is naturally present in our bodies, elevated levels of homocysteine in the blood has been associated with an increased risk of cardiovascular disease and stroke.

B12 prevents loss of neurons

Methionine is synthesized from homocysteine, which has been linked to many neurodegenerative diseases. A high level of homocysteine can lead to brain damage and poor cognitive function. The synthesis of methionine thus prevents the accumulation of this harmful amino acid in the brain.

In addition, B12 is vital for the maintenance of the myelin sheaths that cover and protect the nerves of the central and the peripheral nervous system. This covering ensures fast and effective nerve-impulse transmission. Damage to the myelin sheath due to B12 deficiency typically results in neurological problems later in life.

B12 supports healthy mood

Sufficient vitamin B12 is required for methylation, which is necessary for the production of serotonin as well as other monoamine neurotransmitters and catecholamines. High serum levels of homocysteine and low serum levels of B12 are associated with poor cognitive function, cognitive decline and dementia. Folate and B12 work together to produce S-adenosylmethionine (SAMe), a compound involved in immune function and mood.

Recent studies have shown that B12 supplementation could play an important role in the treatment of mood disorders, particularly when combined with SSRIs.

Symptoms of B12 deficiency usually start slowly and get worse over time. However, it’s also possible to have symptoms of B12 deficiency without having anemia, or to be low in B12 but have no symptoms. This means many people don’t realize they’re low in B12 until their health is compromised. 

Low B12 often leads to low red blood cell production, which in turn can lead to poor energy levels and fatigue. In serious cases, B12 deficiency can contribute to neurological symptoms such as mood disorders, anxiety, and/or nerve pain. Research has shown a fundamental link between low B12, low folate, and major depression. 

Signs that your body is low or deficient in vitamin B12 can include:

• Extreme and/or ongoing fatigue
• Lack of energy
• Poor appetite
• Feeling dizzy or faint
• Headaches
• Numbness or tingling in the limbs
• Dermatitis
• Ringing in the ears
• Feeling out of breath
• Confusion or brain fog
• Anxiety and/or paranoia
• Pale or yellowed skin

• Pernicious anemia
  Pernicious anemia may result when the body produces antibodies that bind to and inhibit the effects of intrinsic factor. This prevents B12 from being absorbed in the ileum (small intestine). 
• Malabsorption
  If the parietal cells in the stomach are damaged in any way (usually by inflammatory bowel disease, Celiac disease or infection) they may be less able to absorb B12 properly.
• Dietary Insufficiency
  A strict vegan diet is a typical cause of B12 deficiency due to the fact that B12 is only present in animal sources. Studies show that around up to 86.5% and 69.1% of ‘strict’ and ‘moderate’ vegans respectively are deficient.
•  Genetic Factors
  MTR and MTRR variants are genetic SNPs (single nucleotide polymorphisms) which may significantly impact the conversion and absorption of B12 in the body. MTHFR mutations affect the body's ability to use vitamin B12 because certain mutations (C667T and A129C) lower the amount of active folate being produced in the body, and the use of vitamin B12 requires the active form of folate, L-Methylfolate.

This is the most important part of the whole matter. Improving your B12 status comes down to the TYPE of B12 you take. 

The recommended daily amount of vitamin B12 for adults is 2.4 micrograms. However, the key is absorption. You might be taking a multivitamin that contains the recommended amount of B12, but if your body can’t absorb it (for any of the reasons mentioned above), you won’t reap any of the benefits. 

How to choose the right B12 supplement