Vitamin B-12, also known as cobalamin, is an essential nutrient in the B-complex of the eight B water-soluble vitamins. This nutrient must be consumed through animal foods  (although supplementation may be more ideal) to ensure adequate intake. Vitamin B-12 is structurally the largest and most complex of all the vitamins that have been discovered, and a surge of research is coming to the forefront displaying its awesome power in human health.
Role of Vitamin B-12
Vitamin B-12 is integral to normal, healthy energy metabolism in all cells of the body, as well as amino acid and fatty acid metabolism. B-12 is also extremely important in a myriad of other vital physiological processes such as brain function, nervous system health, production of the myelin sheath (nerve insulation), red blood cell formation, bone marrow health, and DNA synthesis/regulation.
A unique nutrient, vitamin B-12 isn’t produced by plants, animals, or even fungi. Instead, this essential vitamin is produced only by certain bacteria. Human requirements for vitamin B-12, as set by the Daily Recommended Intake (DRI) are 2-3 micrograms/mcg (microgram is one millionth of one gram) per day,  upwards of 4-7 micrograms/mcg per day in lieu of recent research.
Unfortunately, research demonstrates that intrinsic factor only allows upwards of 1.5 mcg of B-12 absorption per feeding. Keep this in mind when planning your daily meals, and consider quality B-12 supplementation on a daily basis to ensure adequate intake. There is no upper limit on Vitamin B-12 and even extremely high doses of B-12 have been shown to be safe with virtually no side effects.
What Constitutes Deficiency?
Vitamin B-12 is used by the body from the food and/or supplements we intake daily. In a healthy adult, the body can store up to 3 to 5 years worth of vitamin B-12 (a minuscule two to five milligrams in total), in large part because of the efficient use and recycling of B-12 by the liver.
Over 50% of total body reserves are stored in the liver.  This is one of the main reasons why a B-12 deficiency doesn’t show up until years after poor intake. Common blood testing ranges for vitamin B-12 is measured in ng/L (nanograms per liter of blood) and can be ordered by general physicians or online via specialty mail-order test companies. Vitamin B-12 blood range values include: 
|180-914 ng/L||Normal high/low range|
|180-400 ng/L||Conditionally low levels|
|150-180 ng/L||Low levels where disease symptoms start|
Be aware that in older adults levels between 200 and 500 pg /mL may also produce symptoms of vitamin B-12 deficiency. 
Blood testing for B-12 is a very important step everyone should consider doing to be certain that their levels are sufficient for optimal health as well as healthy brain/nervous system function. Though more medical doctors are becoming aware of B-12’s importance and are beginning to test their patients for this crucial vitamin, it’s not something that is widely practiced–yet. Depending on test results and possible symptoms, other simple follow-up blood tests which indirectly test for B-12 status may be suggested, including homocysteine and methylmalonic acid/MMA. 
Researchers have discovered that B-12 deficiency generally occurs in four distinct stages:
Declining blood levels and cell stores.
Low cellular levels.
Functional B-12 imbalance characterized by increased blood level of homocysteine/MMA and a decreased rate of DNA synthesis.
Clinical signs/symptoms of B-12 deficiency like macrocytic anemia, peripheral neuropathy, and neurological disorders may present themselves. Some researchers suggest that diseases attributed to “old age,” such as cognitive decline, loss of mobility and balance, and memory loss, are sometimes synonymous with vitamin B-12 deficiency. In the case of neurological symptoms, cumulative damage due to long-standing deficiency may be irreversible. This impresses the importance of early diagnosis and ensuring adequate blood levels.
Causes of Vitamin B-12 Deficiency
Knowing some of the primary causes of B-12 deficiency can help inform us on how to best prevent or avoid deficiencies. A few are:
Inadequate Dietary Intake
Vitamin B-12 can only be consumed through animal foods and supplements. Children also are at high risk due to inadequate dietary consumption and lower bodily reserves, despite higher requirements per food calorie. Gastritis, stomach abnormalities/surgeries, or hereditary traits may be to blame for
Absent or Low Stomach Hydrochloric Acid
Sufficient HCl is essential, independent of intrinsic factor secretion, for cleaving B-12 from carrier proteins in food. This is thought to be a major cause of deficiency in the elderly, who generally suffer from low stomach acid.
Other causes include:
- Celiac disease leading to small intestine damage causing impaired absorption of vitamin B-12, which is principally absorbed in the ileum.
- Bad bacteria overgrowth in the small intestine, which some research shows can cause malabsorption of B-12.
- Diabetes medication Metformin may interfere with absorption of B-12.
- Parasitic infection, such as Giardiasis, can cause leaching of the vitamin leading to deficiency.
- Genetic factors such as deficiency in the MTHFR gene, transcobalamin (another type of B-12), etc.
- Excessive alcohol intake. 
Symptoms of Vitamin B-12 Deficiency
Knowing some of the common symptoms, mild and severe, of B-12 deficiency can help inform us on how to best prevent or avoid deficiencies. Since it can take years to manifest a clinical deficiency as measured by blood testing, it’s important to note that signs of deficiency can remain silent for some time as bodily B-12 levels are slowly depleted. A few are:
- Pernicious anemia, specifically megaloblastic anemia, which is a second type of anemia that causes dysfunction of the bone marrow’s ability to manufacture red blood cells.
- Neurological impairments such as depression, confusion, disorientation, schizophrenia, ADHD.  
- Memory loss, Alzheimer’s, Parkinson’s, brain fog, cognitive decline, brain shrinkage.
- Increased fatigue.
- Peripheral neuropathy.
- Sexual dysfunction including low libido, low sperm count, ED, low sex hormone levels.
- Paresthesia (tingling sensation in hands, feet, limbs).
- Spinal cord/myelin sheath degeneration.
- Bowel/urinary incontinence.
- Itchy skin. 
One Final Thought
Vitamin B-12 is an incredibly important and integral essential nutrient in human health, especially all manner of neurological health and red blood cell formation. When deficiencies occur in other nutrients, symptoms or disease processes can be reversed with repletion. Vitamin B-12 is so vital and important in brain and nervous system function, that often the damage from deficiency is permanent and irreversible. Daily supplementation that ensures optimal vitamin B-12 intake that far exceeds the minuscule daily requirements as set by the government and scientific health bodies is ideal.
Watch an In-Depth Video on
Everything You Need to Know About Vitamin B-12
Video Length: 60 minutes
by Dr. Edward Group DC, NP, DACBN, DCBCN, DABFM
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