What Is Vitamin B12?
Vitamin B12 is one of the eight B vitamins that are collectively known as the B complex. It contains the element cobalt in its molecular structure, which is why it’s also called cobalamin. Most people get this water-soluble vitamin from animal products like eggs, milk, fish, and shellfish. Unlike many other nutrients, it’s not commonly found in many plants or fungi.
Interestingly, vitamin B12 is actually synthesized in nature by bacteria and single-celled microbes. These are the only organisms that possess the necessary enzymes to produce it. Since the human body cannot manufacture B12, it’s essential to get it from outside sources, including diet, supplements, or, in certain cases, prescription medication. Vitamin B12 is known for its chemically complex structure, making it the most complicated of all vitamins.
The Four Forms of Vitamin B12
Vitamin B12 comes in four different forms:
Hydroxocobalamin
Hydroxocobalamin, also known as vitamin B12a, is produced by bacteria and is the form found in most food sources. This type is frequently used in B12 shots and easily converts to methylcobalamin in the body.
Methylcobalamin
Methylcobalamin is the most bioavailable form, meaning the body can use it readily. It crosses the blood-brain barrier to protect the brain and nerve cells while helping convert homocysteine to methionine—a process crucial for preventing various health conditions.
Cyanocobalamin
Cyanocobalamin is synthesized in the lab through bacterial fermentation. It’s the cheapest option for supplements but not the best because it includes a cyanide molecule necessary for its stability.
Adenosylcobalamin
Adenosylcobalamin (5-deoxyadenosylcobalamin) is a naturally occurring but unstable form of B12. While it’s not stable in tablet form, some high-quality supplement manufacturers offer it in stable liquid form.
How Is Vitamin B12 Absorbed?
When consumed with food, B12 binds to proteins and is freed in the stomach by cells that release gastric acid. This step is bypassed when B12 is taken as a supplement because the vitamin is already in free form. Once freed, B12 binds to a compound called R protein, which transports it from the stomach to the duodenum, the first section of the small intestine.
In the duodenum, B12 separates from the R protein and binds with intrinsic factor, a glycoprotein produced by the stomach and salivary glands. It is then absorbed by the ileum, the last part of the small intestine, and enters the bloodstream as a transcobalamin complex. This complex delivers B12 to the cells that need it. Any unused B12 is eliminated through urine or feces.
What Does Vitamin B12 Do for the Body?
Vitamin B12 plays several crucial roles in the body:
Boosting energy and metabolism
Promoting heart and cardiovascular health
Maintaining healthy brain and nervous system functions
Normalizing mood
Supporting normal bone growth and development
Assisting in DNA production
Helping cells to divide and grow normally
Vitamin B12, Energy, & Metabolism
People often take B12 to boost energy because it acts as a coenzyme in the Krebs cycle, the process the body uses to produce energy. B12 helps break down carbohydrates, particularly glucose sugars, and processes fats. A lack of B12 can lead to high blood sugar and an unhealthy lack of fat.
Vitamin B12 & the Brain
Vitamin B12 is vital for brain health, affecting cognitive function and memory. Myelin, a white fatty substance, protects brain cells from free radicals and other toxins. Insufficient B12 can impair brain and nerve functioning by decreasing the production and maintenance of myelin, causing deterioration in brain function.
Vitamin B12 & Cognitive Health
Studies show that people with cognitive impairment and memory loss often lack B12. Scientists believe that a B12 deficiency might reduce the production of certain neurotransmitters essential for nervous system communication. Ensuring sufficient B12 intake throughout life is crucial as supplementation has not been proven effective after cognitive decline has occurred.
Vitamin B12 & Mood
Research indicates that a B12 deficiency might be linked to mood disorders. Insufficient B12 can reduce the myelin sheaths, which may affect mood. While the precise effect of B12 on major depression is unclear, supplementation might help normalize mood by aiding in the production of mood-regulating neurotransmitters like dopamine, serotonin, and melatonin.
Vitamin B12 & Cardiovascular Health
Vitamin B12 is essential for heart health. Deficiency can lead to macrocytosis, where red blood cells are larger than normal and hemoglobin decreases, leading to less oxygen being delivered throughout the body. This condition is linked to poor circulation, a higher risk of heart disease, and stroke.
Vitamin B12 & Severe Illness
A lack of B12 can affect gene expression and change cellular chromatin, affecting DNA and RNA. Combined with vitamins B6 and B9 (folate), B12 might help reduce the risk of uncontrolled cell proliferation.
Vitamin B12 & Bone Health
Low B12 levels can lead to elevated homocysteine, affecting bone health, density, and cell formation, increasing the risk of fractures in older individuals. Ensuring adequate B12 intake is particularly important for the elderly to maintain bone health.
How Much Vitamin B12 Do You Need?
| Age | RDA | Pregnant | Lactating |
|---|---|---|---|
| 1-3 years | 0.9 mcg | ||
| 4-8 years | 1.2 mcg | ||
| 9-13 years | 1.8 mcg | ||
| 14+ years | 2.4 mcg | 2.6 mcg | 2.8 mcg |
The Institute of Medicine’s Food and Nutrition Board recommends a daily intake of 2.4 mcg for normal adults, 2.6 mcg for pregnant women, and 2.8 mcg for lactating women. Research suggests that the average B12 intake among the U.S. population is about 3.4 mcg/day, higher than the recommended daily intake. However, some people may still be deficient due to digestion, absorption issues, health status, or medication interference.
The human body can absorb up to 1.5 mcg of B12 from food but can absorb higher amounts from supplements, which bypass the digestive process. Although some claim that humans store between 2 to 5 mg of B12 in the liver, lasting up to five years, it’s not advisable to rely on this store alone.
Are There Side Effects From Taking B12?
Vitamin B12 is generally safe with few side effects. It has a biological half-life of about six days, meaning the body eliminates what it can’t use or absorb. Some people may experience minor side effects from B12 shots, such as pain at the injection site, headaches, nausea, diarrhea, and dizziness.
How Can You Get B12?
You can obtain B12 from various foods or as a nutritional supplement in tablet, sublingual, liquid, or injection forms. Hydroxocobalamin or cyanocobalamin injections are common and particularly helpful for severe deficiencies. People who need periodic energy boosts also often rely on injections.
Foods With Vitamin B12
| Food | Serving | Vitamin B12 Content |
|---|---|---|
| Clams, steamed | 3 oz | 84.1 mcg |
| Liver (beef), cooked | 3 oz | 70.7 mcg |
| Mussels, steamed | 3 oz | 20.4 mcg |
| Mackerel, cooked | 3 oz | 16.1 mcg |
| Crab (Alaska king), cooked | 3 oz | 9.8 mcg |
| Beef (plate steak), cooked | 3 oz | 6.9 mcg |
| Trout (wild rainbow), cooked | 3 oz | 5.4 mcg |
| Salmon (sockeye), cooked | 3 oz | 4.8 mcg |
| Tuna (light, packed in water) | 3 oz | 2.5 mcg |
Vitamin B12 Supplements
Many people find it challenging to get enough B12 from their diet alone. Older individuals and those with certain health conditions may have absorption issues. If you’re one of these people, you might want to consider a daily supplement. For effective supplementation, look for a blend of methylcobalamin, adenosylcobalamin, and hydroxocobalamin, which offers improved bioavailability.
What Is Vitamin B12 Deficiency?
A B12 deficiency can arise from factors like a vegetarian diet or an autoimmune disease that hinders B12 absorption. Long-term use of acid-inhibiting medications can also reduce levels of intrinsic factor, further inhibiting absorption.
When the body lacks B12, homocysteine and methylmalonic acid (MMA) levels increase, which are often measured in lab tests to diagnose deficiency.
What Are the Symptoms of Vitamin B12 Deficiency?
Symptoms vary and can include:
Confusion, disorientation, brain fog
Memory loss, dementia, or cognitive decline
Paresthesia (tingling in the limbs)
Peripheral neuropathy (loss of feeling in limbs)
Loss of balance
Excessive fatigue
Bowel/urinary tract incontinence
Tongue soreness
Appetite loss
Constipation
Diarrhea
Learning or developmental disorders in kids
Weak immune system
Brittle, flaky nails
Dry skin
Low red blood cell count (anemia)
What Is Megaloblastic Anemia?
Megaloblastic anemia occurs when the bone marrow produces oversized, immature red blood cells lacking enough hemoglobin to carry oxygen. This happens due to a vitamin B12 deficiency, vital for converting homocysteine to tetrahydrofolate (THF) for DNA synthesis and cell division. Even with folate supplementation, this type of anemia persists until the B12 deficiency is corrected.
What Is Pernicious Anemia?
Pernicious anemia is a form of megaloblastic anemia where the body doesn’t produce intrinsic factor, often due to an autoimmune disorder called atrophic gastritis. Without intrinsic factor, B12 can’t be absorbed, leading to a lack of healthy red blood cells. This condition can co-occur with other autoimmune disorders and worsen over time, eventually leading to fatigue, brain fog, and other severe symptoms.
Risk Factors for Vitamin B12 Deficiency
Several factors can increase the risk of B12 deficiency:
Vegetarian Diet
Since plant foods don’t naturally contain B12, vegetarians and vegans are at a higher risk. Consuming B12-fortified foods or taking supplements can help meet their needs.
Genetic Predisposition
Inherited disorders like MTHFR gene mutations can hinder B12 absorption. Other congenital issues, such as Imerslund-Gr?sbeck syndrome, can also cause deficiencies.
Age
People over 50 produce less hydrochloric acid, affecting B12 absorption. This can be exacerbated by medications like proton pump inhibitors.
Gastrointestinal Disease
Conditions like Crohn’s disease or celiac disease can impair B12 absorption. Surgical removal of parts of the stomach or intestine further complicates this.
Medications
Some medications, especially those for diabetes or peptic ulcers, can inhibit B12 absorption, leading to deficiency.
Are You Vitamin B12 Sufficient or Deficient?
Various factors can interfere with normal B12 absorption, leading to deficiency. Blood level testing is the most accurate way to determine if you’re deficient. Here’s a general guideline for blood levels:
| Level of Vitamin B12 in Blood | Severity |
|---|---|
| 450+ ng/L | Healthy/optimal |
| 180-400 ng/L | Conditionally low levels |
| 150-180 ng/L | Low levels where disease symptoms start |
Based on your test results and symptoms, additional blood tests like homocysteine and methylmalonic acid (MMA) levels might be recommended to provide a comprehensive assessment of your B12 status.
