Vitamin B12: Understanding an essential nutrient

Vitamin B12, also known as cobalamin, is a nutrient that plays a vital role in several key metabolic functions: maintaining the health of the nervous system, producing red blood cells, and synthesizing DNA. It is unique among vitamins due to its intricate absorption mechanism, requiring specific binding proteins and receptors to be absorbed efficiently. B12 is found naturally in animal products such as meat, fish, eggs, and dairy, but not in plants. This is why people who follow plant-based diets are at risk for B12 deficiency.

The role of B12 in the body

Vitamin B12 is necessary for the formation of red blood cells, ensuring they are the right size and shape to transport oxygen properly throughout the body. Without adequate B12, red blood cells can become malformed, leading to pernicious anemia.

Another critical function of B12 is in maintaining the health of the nervous system. B12 is essential for the production of myelin, the protective sheath that covers nerve fibres, ensuring the smooth transmission of nerve impulses. Without sufficient B12, individuals can experience neurological issues such as numbness, tingling, and even cognitive disturbances.

Vitamin B12 also plays a significant role in DNA synthesis and cell division. It works synergistically with folate (vitamin B9) to ensure the proper replication and repair of DNA. This is vital for all cellular function, affecting everything from skin health to immune system efficiency.

Food Sources

• Meat: Beef, liver, and poultry are excellent sources of B12.

• Fish: Salmon, trout, and tuna contain high levels of B12.

• Dairy: Milk, cheese, and yogurt provide moderate amounts of B12.

• Eggs: While not as high in B12 as meat or fish, eggs are still a valuable source.

For those who do not consume animal products, fortified foods and supplements are vital. Fortified foods, for example some cereals, nutritional yeast, and plant-based milks, can provide B12, but this is always the synthetic form. These sources may not be enough, so additional supplementation is often needed.

Forms of B12 supplements

• Cyanocobalamin: The most common form of B12 supplement, easily absorbed by the body.

• Methylcobalamin: A bioactive form of B12 that is readily used by the body, particularly beneficial for neurological health.

• Hydroxycobalamin: Often used in injections.

Supplemental B12 doesn’t appear to carry any risk of toxicity.

Recognizing the signs of B12 deficiency:

• Fatigue and weakness

• Shortness of breath

• Pale or jaundiced skin

• Numbness and tingling in the hands and feet

• Cognitive difficulties and memory loss

• Balance issues

 Symptoms can range from mild to severe.

The complex path of B12 absorption

When B12 is ingested in food, hydrochloric acid and pepsin in the gastric juices in the stomach release B12 from the protein matrix in which it is bound.

Once liberated from food, B12 binds to proteins secreted by the salivary glands and the stomach lining. These proteins protect B12 from the acidic environment of the stomach, allowing it to survive and reach the small intestine.

The next critical step occurs in the duodenum, the first part of the small intestine. Here, pancreatic enzymes release the B12, and then it binds to intrinsic factor, another protein produced in the stomach. Intrinsic factor is essential for the efficient absorption of B12, but the catch 22 is that we need B 12 to make that intrinsic factor!

The B12-intrinsic factor complex travels down the small intestine to the ileum, where specific receptors bind it, allowing uptake into the intestinal cells. Then a transporter protein delivers it to the liver: its main storage site. The liver can store several years' worth of B12, ensuring a steady supply for the body's needs.

As you see, there are many steps along this complicated pathway that may interfere with proper absorption, including:

• Age: As we age, the production of intrinsic factor and stomach acid may decrease, leading to impaired absorption.

• Medical conditions such as pernicious anemia, Crohn's disease, and atrophic gastritis can interfere with B12 absorption.

• Certain medications, including proton pump inhibitors and metformin, can affect B12 absorption.

• Strict vegetarian or vegan diets lack adequate B12 sources, necessitating supplementation.

Because absorption of Vitamin B12 is such a complex process, adequate dietary intake and proper functioning of the gastrointestinal tract are essential. B12 is often included in multivitamins, but it’s not necessarily well absorbed from them. If you eat animal products and are still are still deficient in B12, a multi won’t help because the problem is with absorption, not intake.

The good news is that it can be taken sublingually, to be directly absorbed by the large blood vessel under the tongue. Many people prefer B12 injections because they bypass the body's absorption mechanisms completely. Our patients often report feeling a real boost after receiving a B12 shot.