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Vitamin B12 (Cobalamin)

Vitamin B12: A Comprehensive Review of Its Many Health Benefits

Vitamin B12, also known as cobalamin, is a crucial nutrient that plays a vital role in the proper functioning of the human body. It is one of eight B vitamins and has the largest and most complex chemical structure of all the vitamins. Vitamin B12 is unique among vitamins in that it contains a metal ion, cobalt and it is not produced exogenously (in the body) and must be primarily obtained from dietary bacterial sources. It is essential for the production of red blood cells, the maintenance of the nervous system, and the synthesis of RNA and DNA, the body's genetic material. It also helps the body convert food (carbohydrates) into fuel (glucose), which is used to produce energy. These B vitamins, often referred to as B complex vitamins, also help the body use fats and protein. Vitamin B12 works in conjunction with Vitamin B9 to aid in the production of red blood cells and improve iron utilisation in the body. Together, B12 and B9 produce S-adenosylmethionine (SAMe), a compound that is important for immune function and mood regulation.

Vitamin B12 deficiency is a common problem due to limited dietary intake, malabsorption, medical conditions, or the use of B12-depleting medications, particularly among vegetarians, vegans, and the elderly. These individuals require vitamin B12-fortified foods or supplements to meet their nutritional needs. The deficiency of Vitamin B12 is often overlooked and misdiagnosed and can lead to various health complications including macrocytic anemia, neurological complications, osteopenia, neurocognitive impairment, and increased vascular disease risk associated with elevated homocysteine. Vitamin B12 deficiency also causes elevated levels of holotranscobalamin II and methylmalonic acid. Vitamin B12 is found almost exclusively in animal-based foods and is therefore a nutrient of potential concern for those following a vegetarian or vegan diet. Finally, vitamin B12 deficiency results in loss of intestinal villi, aggravating malabsorption of B12. Studies have shown that the use of vitamin B12 supplements are more effective at maintaining healthy levels of B12 than food.

Vitamin B12 is absorbed in the stomach through a complex process involving hydrochloric acid (HCL) and the enzyme protease. The HCL helps to unbind Vitamin B12 from protein and create an acidic environment in the stomach that is necessary for its release. Once released, Vitamin B12 binds to intrinsic factor, a glycoprotein produced by parietal cells in the stomach. This B12-intrinsic factor complex is then absorbed in the ileum (the last part of the small intestine) for use by the body. Individuals with low levels of HCl in the stomach due to aging, certain medical conditions, regular alcohol consumption, and/or use of acid-reducing medications may have difficulty absorbing vitamin B12 and may require vitamin B12 supplements. People who regularly take medications that suppress stomach acid for conditions like gastroesophageal reflux disease (GERD) or peptic ulcer disease—such as proton-pump inhibitors, H2 blockers, or other antacids—may also have difficulty absorbing vitamin B12 from food. Individuals with chronic stomach inflammation also have difficulty with vitamin B12 absorption. The absorption rate of vitamin B12 is around 50% for doses less than 1-2 mcg, but drops significantly at higher doses. For example, at 500 mcg the absorption rate is only 2% and at 1,000 mcg it is 1.3%. Vitamin B12 is stored in large amounts in the liver, and deficiency can take 3-5 years to develop if intake stops. However, in cases where deficiency is caused by a lack of intrinsic factor, high-dose supplementation may be necessary.

Natural dietary sources of vitamin B12 (cobalamin)

Here are some natural dietary sources of vitamin B12:

  • Clams: Clams are a good source of vitamin B12, with a 100-gram serving of clams providing about 98 micrograms (mcg) of vitamin B12.

  • Liver: Liver is a good source of vitamin B12, with a 100-gram serving of liver providing about 84 mcg of vitamin B12.

  • Meat: Meat is a good source of vitamin B12, with a 100-gram serving of beef, for example, providing about 3 micrograms (mcg) of vitamin B12.

  • Fish: Fish is a good source of vitamin B12, with a 100-gram serving of salmon, for example, providing about 2.5 mcg of vitamin B12.

  • Chicken: Chicken is a good source of vitamin B12, with a 100-gram serving of chicken breast providing about 1.5 mcg of vitamin B12.

  • Dairy products: Dairy products such as milk, cheese, and yogurt are good sources of vitamin B12. A cup of milk, for example, provides about 1.2 mcg of vitamin B12.

  • Fortified foods: Many foods are fortified with vitamin B12, including some types of bread and cereals.

It is worth noting that the amount of vitamin B12 you can obtain from food varies based on factors such as the soil in which it was grown, the processing methods used, the form in which it is present, and the presence of other substances that may interfere its absorption. Despite high amounts in dietary sources, only a small fraction of cobalamin is absorbed in healthy individuals.

While consuming a varied diet consisting of whole, unprocessed fruits, vegetables, nuts, seeds, and other plant-based foods is essential for obtaining a comprehensive range of nutrients, cobalamin (Vitamin B12), supplementing with the methylated, bioavailable forms of mecobalamin (co-methylcobalamin) and hydroxocobalamin can have additional benefits. It may help fill any nutritional gaps, ensure adequate intake for those with dietary restrictions, and provide added support for certain health conditions. Additionally, supplementing can increase the bioavailability of cobalamin in the body. Therefore, it is worthwhile considering supplementing in consultation with a health professional and a balanced diet for optimal health.

The role of vitamin B12 in brain function

Vitamin B12 is an essential nutrient that plays a critical role in brain function. It is involved in the maintenance of the myelin sheath, a protective layer that surrounds nerve cells, and the synthesis of neurotransmitters, chemicals that transmit messages between neurons. Studies have shown that a deficiency of vitamin B12 can lead to cognitive decline and an increased risk of dementia.

In a study of older adults with mild cognitive impairment, daily supplementation with vitamin B12, along with folic acid and vitamin B6, significantly improved memory and cognitive function. This suggests that vitamin B12 may play a role in preventing brain atrophy, which is the loss of neurons in the brain and often associated with memory loss or dementia.

Additionally, several studies have investigated the relationship between vitamin B12 and cognitive decline in patients with early-stage dementia. One study found that a combination of vitamin B12 and omega-3 fatty acid supplements slowed mental decline. Another study found that even vitamin B12 levels on the low side of normal can contribute to poor memory performance.

It should be noted that while supplementing with vitamin B12 may improve memory, even in the absence of a clinically diagnosed deficiency, it is only effective in patients with pre-existing deficiency. This highlights the importance of regular monitoring of vitamin B12 levels, especially in older adults and individuals at risk of cognitive decline.

The role of vitamin B12 in cardiovascular health

In addition to its role in brain function, vitamin B12 has also been shown to have positive effects on cardiovascular health. A deficiency of vitamin B12 has been linked to an increased risk of high homocysteine levels, a known risk factor for cardiovascular disease. This is due to the inhibition of methylmalonyl-CoA mutase and methionine synthase, resulting in increased concentration of methylmalonic acid and homocysteine.

Supplementation with vitamin B12 has been shown to lower homocysteine levels and improve markers of cardiovascular health, such as blood pressure and cholesterol levels. Studies have also demonstrated impaired arterial endothelial function and increased carotid intima-media thickness, which are surrogates of atherosclerosis, in populations with metabolic vitamin B12 deficiency.

Research suggests that individuals with elevated homocysteine levels have a higher risk of developing coronary artery disease and experiencing a stroke, with some studies indicating a potential doubling and 2.5 times increase in risk, respectively. Lowering homocysteine levels can be achieved through the intake of B complex vitamins, particularly B9, B6, and B12. Thus, adequate intake of vitamin B12 can help in reducing the risk of heart disease.

The role of vitamin B12 in the prevention of certain diseases

Vitamin B12 is a vital nutrient that plays a crucial role in the maintenance of overall health. Studies have shown that deficiency of vitamin B12 can lead to an increased risk of various diseases, such as osteoporosis and certain types of cancer.

Osteoporosis is a condition characterized by weak bones that are prone to fracture. In a study of postmenopausal women, daily supplementation with vitamin B12 significantly increased bone mineral density and reduced the risk of osteoporotic fractures. Additionally, one study involving more than 2,500 adults showed that individuals with a vitamin B12 deficiency also had lower than normal bone mineral density. These findings suggest that adequate intake of vitamin B12 may help in preventing osteoporosis.

Vitamin B12 deficiency has also been linked to an increased risk of certain types of cancer, such as breast, colon, and lung cancer. While there is currently no evidence that Vitamin B12 alone reduces the risk of breast cancer, population studies have demonstrated that women who consume more folate in their diet have a lower risk of breast cancer. Vitamin B12 works in conjunction with folate in the body and may contribute to reducing breast cancer risk. An additional preliminary study suggests that postmenopausal women with the lowest dietary intake of B12 may have an increased risk of breast cancer.

Macular degeneration is an eye disease that mainly affects central vision. Researchers believe that supplementing with vitamin B12 may lower homocysteine, a type of amino acid that is found in the bloodstream. Elevated homocysteine levels have been associated with an increased risk of age-related macular degeneration. Additionally, low B12 levels might co-cause high homocysteine levels leading to erectile dysfunction. Adequate intake of vitamin B12 may help in reducing the risk of these diseases.

Vitamin B12 and energy production

Vitamin B12 is essential for the production of energy in the body. It plays a critical role in the metabolism of carbohydrates, fats, and proteins, and is involved in the synthesis of ATP, the primary energy source for cells. A deficiency of vitamin B12 can lead to fatigue and weakness, as the body is unable to produce energy efficiently. Fatigue is a common symptom of vitamin B12 deficiency. All B vitamins play an important role in the body's energy production, though they do not provide energy themselves.

Some studies have suggested that certain individuals who do not have a deficiency in B12 may experience an increase in energy from B12 shots. Additionally, preliminary research indicates that individuals with chronic fatigue syndrome may benefit from B12 injections. In a study of individuals with fatigue, daily supplementation with vitamin B12 resulted in significant improvements in energy levels and quality of life. However, it is important to note that currently, there is no scientific evidence to suggest that vitamin B12 supplements can boost energy in those with sufficient levels of this vitamin.

It is also important to note that since vitamin B12 is water-soluble, the body cannot store extra amounts. Any excess passes through the body and is eliminated when you urinate. On the other hand, if you are significantly deficient in vitamin B12, taking a supplement or increasing your intake will likely improve your energy level. In fact, one of the most common early signs of vitamin B12 deficiency is fatigue or lack of energy. Additionally, when the body doesn't have enough healthy red blood cells to carry oxygen to tissues, anemia can occur, leading to feelings of weakness and tiredness.

Vitamin B12 and macrocytic or megaloblastic anaemia & pernicious anaemia

Pernicious anemia is a form of vitamin B12 deficiency that occurs as a result of an autoimmune disorder. In individuals with this condition, the body's immune system mistakenly produces antibodies that attack and destroy the stomach cells responsible for the production of intrinsic factor, a protein necessary for the absorption of vitamin B12. This leads to a decrease in intrinsic factor levels and a decreased ability to absorb vitamin B12.

Vitamin B12 plays a crucial role in the production of red blood cells, which transport oxygen throughout the body. A deficiency of vitamin B12 can lead to the development of megaloblastic anemia, characterized by the presence of larger, oval-shaped red blood cells that are unable to move from the bone marrow into the bloodstream at an appropriate rate. This leads to symptoms such as fatigue and weakness.

Prolonged deficiency, whether caused by pernicious anaemia or dietary deficiencies, can result in macrocytic anemia and subacute combined degeneration of the spinal cord. These complications can be fatal if left untreated. Supplementation with vitamin B12 can alleviate symptoms and treat anaemia, making early diagnosis and treatment of pernicious anaemia essential. It's important to note that it's essential to diagnose and treat pernicious anaemia early in order to prevent the development of serious complications.

Vitamin B12 and mental health

Vitamin B12 has also been shown to have positive effects on mental health. The exact mechanism by which vitamin B12 impacts mood is not yet fully understood. However, it plays a vital role in synthesizing and metabolizing serotonin, a chemical responsible for regulating mood. Therefore, vitamin B12 deficiency may lead to decreased serotonin production, which may cause a depressed mood.

A deficiency of vitamin B12 has been linked to an increased risk of depression and anxiety. In a study of individuals with depression, daily supplementation with vitamin B12 resulted in significant improvements in mood and symptoms of depression. Another study discovered that vitamin B12 deficiency was associated with twice the risk of severe depression.

Vitamin B12 may also help to reduce the risk of developing psychiatric disorders, such as schizophrenia. Additionally, high vitamin B12 levels have been linked to better treatment outcomes and an increased probability of recovery from major depressive disorder (MDD).

It is important to note that while vitamin B12 supplements may help improve mood and depression in people with a deficiency, research does not currently suggest that they have the same effect in those with normal B12 levels. 

Vitamin B12 and fertility

Vitamin B12 is essential for fertility and plays a critical role in the production of hormones and the proper functioning of the reproductive system. Adequate levels of vitamin B12 are crucial for the healthy development and maturation of sperm and eggs. A deficiency of vitamin B12 has been linked to fertility problems in both men and women.

In men, vitamin B12 deficiency has been linked to decreased sperm count and motility. Studies have shown that daily supplementation with vitamin B12 can result in significant improvements in sperm count and motility in infertile men. Additionally, low vitamin B12 levels have been associated with poor sperm quality and decreased sperm DNA integrity.

In women, vitamin B12 deficiency has been linked to decreased fertility and hormonal imbalances. This is due to vitamin B12's role in the formation of red blood cells, which are crucial for the healthy function of the reproductive system. Additionally, vitamin B12 deficiency can disrupt the proper functioning of the reproductive system, leading to problems with ovulation and implantation.

Vitamin B12 and pregnancy

Adequate levels of vitamin B12 are crucial for a healthy pregnancy. This essential nutrient plays a critical role in the health of both the mother and the developing fetus during pregnancy. It is involved in the synthesis of DNA and the proper development of the nervous system. A deficiency of vitamin B12 during pregnancy has been linked to an increased risk of birth defects, preterm delivery, and low birth weight.

Studies have shown that the developing fetus's brain and nervous system require sufficient B12 levels from the mother to develop properly. Vitamin B12 deficiency in the early stages of pregnancy may increase the risk of neural tube defects and other birth defects. Additionally, maternal vitamin B12 deficiency may contribute to premature birth or miscarriage. One study found that women with vitamin B12 levels lower than 250 pg/mL were three times more likely to give birth to a child with birth defects, compared to those with adequate levels. For women with a vitamin B12 deficiency and levels below 150 pg/mL, the risk was five times higher, compared to women with levels above 400 pg/mL.

Vitamin B12 and the immune system

Vitamin B12 is essential for maintaining a healthy immune system. It plays a critical role in the production of white blood cells, which are crucial for the immune system to function properly. A deficiency of vitamin B12 can lead to a decrease in white blood cells and thus, an impaired immune response. This can result in an increased risk of infections, such as pneumonia and sepsis, as well as other immune-related disorders, such as anaemia, and increased risk of chronic diseases.

Research has shown that individuals with vitamin B12 deficiency have higher rates of infections, particularly in older adults and people with chronic conditions. Studies have also suggested that vitamin B12 supplementation may help to boost the immune system and reduce the risk of infections by increasing white blood cell production and activity.

Vitamin B12 also plays a role in the production of antibodies, which are essential for fighting off pathogens and infections. Additionally, B12 plays a role in regulating the immune response by modulating the activity of T-cells and natural killer cells.

Vitamin B12 and skin, hair and nail health.

Given its role in cell production, vitamin B12 is essential for the maintenance of healthy hair, skin and nails. Adequate levels of this vitamin are necessary to promote optimal hair, skin and nail health. However, a deficiency of vitamin B12 can result in various dermatologic symptoms, such as hyperpigmentation, nail discoloration, hair changes, vitiligo, and angular stomatitis.

Research has also shown that vitamin B12 may have positive effects on skin health. It has been shown to improve the appearance of acne, eczema, and other skin conditions. In a study of individuals with acne, daily supplementation with vitamin B12 resulted in significant improvements in the appearance of the skin. Additionally, some studies suggest that vitamin B12 may help to reduce the risk of certain skin cancers, such as basal cell carcinoma and squamous cell carcinoma, by modulating the activity of the immune system.

It is important to note that if an individual is well-nourished and not deficient in vitamin B12, taking a supplement is unlikely to have a significant impact on the skin, nail strength, or hair health.

What are the symptoms of vitamin B12 deficiency?

Vitamin B12, also known as cobalamin, is an essential nutrient that plays a role in various bodily functions, including the production of red blood cells, the maintenance of the nervous system, and DNA synthesis. Deficiency in vitamin B12 can cause a range of symptoms, including:

  • Anemia: A deficiency in vitamin B12 can cause anemia, which is a condition in which the body does not have enough red blood cells to carry oxygen to the body's tissues. Symptoms of anemia include fatigue, pale skin, and shortness of breath.

  • Headaches: A deficiency in vitamin B12 can cause headaches.

  • Weakness: A deficiency in vitamin B12 can cause weakness and difficulty walking.

  • Numbness and tingling: A deficiency in vitamin B12 can cause numbness and tingling in the hands and feet.

  • Memory loss: A deficiency in vitamin B12 can cause memory loss and difficulty concentrating.

  • Mood changes: A deficiency in vitamin B12 can cause mood changes, such as depression or irritability.

If you think you may have a deficiency in vitamin B12, it is important to speak with a health professional for proper diagnosis and treatment. They can recommend appropriate supplements and make dietary recommendations to help you meet your nutritional needs.

What are the potential side effects of taking vitamin B12 supplements?

Vitamin B12, also known as cobalamin, is generally safe to consume in recommended amounts. However, taking excessive amounts of vitamin B12 can cause side effects, including:

  • Digestive symptoms: Consuming large amounts of vitamin B12 can cause digestive symptoms, such as stomach cramps and diarrhea.

  • Skin reactions: Some people may develop skin reactions, such as rash or hives, after taking high doses of vitamin B12.

  • Allergic reactions: Some people may be allergic to vitamin B12. Symptoms of an allergic reaction may include rash, itching, and difficulty breathing.

  • Increased risk of certain cancers: Some research suggests that taking high doses of vitamin B12 may increase the risk of certain types of cancer, such as breast and prostate cancer. However, more research is needed to fully understand this relationship.

It is important to note that these side effects are typically associated with taking large amounts of vitamin B12, well above the recommended daily intake. It is important to speak with a health professional before taking vitamin B12 supplements to ensure that you are taking the appropriate amount.

Vitamin B12 supplements are generally well tolerated and have a low risk of side effects. However, as with any supplement, it is important to speak with a health professional before starting to ensure that they are safe and appropriate for you.

Can vitamin B12 supplements interact with other medications or supplements?

Yes, vitamin B12 supplements can interact with certain medications and supplements. Some medications and supplements that may interact with vitamin B12 include:

  • Chloramphenicol: This is an antibiotic medication. Taking vitamin B12 supplements along with chloramphenicol can interfere with the absorption of the antibiotic.

  • Proton pump inhibitors (PPI's): These are medications that reduce stomach acid production, such as omeprazole and lansoprazole. Taking vitamin B12 supplements along with proton pump inhibitors can interfere with the absorption of the vitamin.

  • Metformin: This is a medication used to treat type 2 diabetes. Taking vitamin B12 supplements along with metformin can interfere with the absorption of the medication.

  • Colchicine: This is a medication used to treat gout. Taking vitamin B12 supplements along with colchicine can interfere with the absorption of both the medication and the supplement.

  • Other supplements: Some supplements, such as large doses of calcium and zinc, may interfere with the absorption of vitamin B12. It is important to speak with a health professional about potential interactions between vitamin B12 and any other supplements you are taking.

It is important to speak with a health professional before taking vitamin B12 supplements to ensure that they are safe and appropriate for you. They can help you understand any potential interactions with other medications or supplements you are taking.

Is it safe to take vitamin B12 supplements if I have a particular health condition?

Vitamin B12, also known as cobalamin, is an essential nutrient that is necessary for various bodily functions. However, it is important to speak with a health professional before taking vitamin B12 supplements to ensure that they are safe and appropriate for you, particularly if you have a particular health condition. Some conditions that may be affected by vitamin B12 include:

  • Anemia: Vitamin B12 is necessary for the production of red blood cells. If you have anemia, taking vitamin B12 supplements may be beneficial. However, it is important to speak with a health professional about the appropriate amount to take.

  • Pregnancy: It is important to get enough vitamin B12 during pregnancy to support fetal development. However, taking excessive amounts of vitamin B12 during pregnancy may not be safe. It is important to speak with a health professional about the appropriate amount of vitamin B12 to take during pregnancy.

  • Malabsorption disorders: If you have a condition that affects your body's ability to absorb nutrients, such as celiac disease or inflammatory bowel disease, you may be at risk for a deficiency in vitamin B12. Taking vitamin B12 supplements may be beneficial in these cases, but it is important to speak with a health professional about the appropriate amount to take.

  • Kidney disease: If you have kidney disease, your body may have difficulty processing vitamin B12. This can lead to an accumulation of the nutrient in the body and potentially cause side effects. It is important to speak with a health professional about the appropriate amount of vitamin B12 to take if you have kidney disease.

  • The elderly: A common occurrence in older adults is a decrease in the production of hydrochloric acid in the stomach, which can lead to reduced absorption of Vitamin B12. If an individual is experiencing difficulties absorbing Vitamin B12, a health professional may recommend intramuscular injections to increase their levels.

It is always important to speak with a health professional before starting any new supplement to ensure that it is safe and appropriate for you.


Vitamin B12 is an essential nutrient that has many health benefits, including its role in brain function, cardiovascular health, the prevention of certain diseases, energy production, red blood cell production, mental health, and fertility. It is especially important for vegetarians, vegans, and the elderly, as they are at a higher risk of deficiency. Supplementation with vitamin B12 has been shown to improve memory and cognitive function, lower homocysteine levels, increase bone mineral density, reduce the risk of certain cancers, improve energy levels and quality of life, treat anemia, improve mood and symptoms of depression, and reduce the risk of psychiatric disorders. It is also essential for the proper functioning of the reproductive system.

It is important to note that while vitamin B12 is essential for maintaining good health, excessive intake of vitamin B12 supplements can be toxic and lead to adverse effects. Therefore, it is crucial to consult with a health professional before taking any vitamin B12 supplements or other nutritional supplements, especially if you are currently taking any medications or supplements, or if you have any underlying medical conditions.

It is also essential to monitor for signs of vitamin B12 deficiency, as even levels within the lower normal range may indicate a progression towards deficiency. Health professionals should re-evaluate the significance of suboptimal vitamin B12 levels and weigh the benefits of B12 treatment. Your health professional can help you determine if vitamin B12 is safe and appropriate for you, based on your individual circumstances and medical history.

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