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B12 Deficiency Symptoms: Everything You Need to Know

Written by Dr. Group, DC Founder
A tired individual. Fatigue and low energy are one of few signs of Vitamin B12 deficiency symptoms.

Vitamin B12, also known as cobalamin, is one of eight water-soluble vitamins collectively known as the B-complex. As an essential nutrient, B12 must be consumed since your body does not make it. If you struggle with fatigue or are down in the dumps, you might wonder whether they are symptoms of vitamin B12 deficiency. Recent research indicates that B12 deficiency is more common than previously thought — up to 40 percent of the U.S. population.

Vitamin B12 is structurally one of 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. Because you can only obtain B12 from animal foods[1], supplementation is ideal.

Role of Vitamin B12 in Human Health

Vitamin B12 is integral to normal, healthy energy metabolism in all cells of the body, as well as amino acid and fatty acid metabolism. B12 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 B12 isn't produced by plants, animals, or even fungi. Instead, this essential vitamin is produced only by certain bacteria that happen to live inside of animals; the cobalamin binds to animal muscle tissue and organs. While bacteria in the human gut produce a small amount, it gets excreted rather than utilized. The Recommended Daily Allowance (RDA) as set by Food and Nutrition Board of the Institute of Medicine, established the minimum daily requirement as 2 to 3 micrograms/mcg (a microgram is one millionth of one gram) per day.[2]

Research demonstrates that intrinsic factor — a glycoprotein that enables B12 from food to survive the acidic stomach — only allows upwards of 1.5 mcg of B12 absorption in a given meal. Keep this in mind when planning your daily meals, and consider quality B12 supplementation on a daily basis to ensure adequate intake. Look for products containing methylcobalamin and adenosylcobalamin for best results.

There is no upper limit on Vitamin B12 and even extremely high doses of B12 have been shown to be safe with virtually no side effects. As a water-soluble vitamin, excess gets excreted daily in your urine.

What Constitutes Deficiency?

Vitamin B12 is obtained from food and supplements. In a healthy adult, the body can store 2 to 5 milligrams, in large part because of the efficient use and recycling of B12 by the liver. Over 50 percent of total body reserves are stored in the liver.[3] This is one of the main reasons why a B-12 deficiency doesn’t show up until years after poor intake.

According to research by the United States Department of Agriculture (USDA) nearly 40 percent of people may have low-normal levels, at which neurological symptoms may appear.[4] The study found that nine percent were clinically deficient, 16 percent were borderline. Even people in the low-normal group may start to see some mild deficiency symptoms, according to the researchers. The good news was that supplementation raised levels.

Common blood tests measure vitamin B12 in ng/L (nanograms per liter of blood) and can be ordered by healthcare providers or online via specialty mail-orde companies. Vitamin B12 blood range values include:[4]

180–914 ng/L Normal high/low range
450+ ng/L Healthy/optimal
180–400 ng/L Conditionally low levels
150–180 ng/L Low levels

In older adults, levels between 200 and 500 ng/mL may also produce vitamin B12 deficiency symptoms.[5]

Everyone should consider blood testing for B12 to ensure that your levels are sufficient for optimal overall health, particularly healthy brain and nervous system function. Although 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 B12 status may be suggested, including homocysteine and methylmalonic acid (MMA).[6]

Deficiency Stages

Researchers have discovered that B12 deficiency generally occurs in four distinct stages:

Stage 1

Declining blood levels and cell stores.

Stage 2

Low cellular levels.

Stage 3

Functional B12 imbalance characterized by increased blood level of homocysteine/MMA and a decreased rate of DNA synthesis.

Stage 4

Clinical signs and symptoms of B12 deficiency, like macrocytic anemia, peripheral neuropathy, and neurological disorders, may present themselves at this stage. Some researchers suggest that diseases attributed to “old age,” such as cognitive decline, memory loss, and changes in mobility and balance are sometimes synonymous with vitamin B12 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 B12 Deficiency

Knowing some of the primary causes of B12 deficiency can help inform us on how to best prevent or avoid deficiencies. A few are:

Inadequate Dietary Intake

Vitamin B12 can only be consumed through animal foods and supplements.

Children also are at high risk of B12 deficiency due to inadequate dietary consumption and lower bodily reserves. Gastritis, stomach abnormalities, stomach surgeries, or hereditary traits may cause impaired absorption.

Absent or Low Stomach Hydrochloric Acid (HCl)

Sufficient stomach acid (HCl) is essential, independent of intrinsic factor secretion, for cleaving or separating B12 from carrier proteins in food. This is thought to be a major cause of deficiency in the elderly, who often have low stomach acid.

Other causes of B12 deficiency include:

  • Celiac disease often causes small intestine damage, which impairs absorption of vitamin B12 — principally absorbed in the ileum.
  • Bad bacteria overgrowth in the small intestine, which some research shows can cause malabsorption of B12.
  • The diabetes medication metformin may interfere with absorption of B12.
  • Parasitic infection, such as giardiasis, can cause leaching of the vitamin, leading to deficiency.
  • Genetic factors such as deficiency in the MTHFR gene.
  • Excessive alcohol intake.[7]

Signs & Symptoms of Vitamin B12 Deficiency

YouTube Video

Signs of B12 Deficiency

Length: 3 minutes

Knowing some of the common signs and symptoms, mild and severe, of B12 deficiency can help inform us on how to best prevent or avoid it. Since it can take years to manifest a clinical deficiency as measured by blood testing, it's important to note that signs can remain silent for some time as bodily B12 levels are slowly depleted. A few that you may or may not notice outwardly include:

  • Pernicious anemia, specifically megaloblastic anemia, which causes dysfunction of the bone marrow's ability to manufacture red blood cells.
  • Neurological impairments such as depression, confusion, disorientation, schizophrenia, ADHD.[8, 9]
  • 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 (erectile dysfunction), low sex hormone levels.
  • Paresthesia (tingling sensation in hands, feet, limbs).
  • Spinal cord/myelin sheath degeneration.
  • Insomnia.
  • Bowel/urinary incontinence.
  • Itchy skin.[10]

One Final Thought

Vitamin B12 is an incredibly important and integral essential nutrient in human health, especially neurological health and red blood cell formation.

Vitamin B12 is so vital and important in brain and nervous system function, that the damage from deficiency is permanent and irreversible. Daily supplementation ensures you get a vitamin B12 intake that exceeds the minuscule daily requirements as set by the government and scientific health bodies.

Finding a quality B12 supplement can prove especially challenging for those following a plant-based diet, as most B12 supplements are actually derived from animal sources. That’s why I created our Vitamin B12 supplement. It’s a vegan-safe formula that contains methylcobalamin and adenosylcobalamin, but also contains hydroxocobalamin for long-lasting, sustained support with 5,000 mcg of B12 per serving. It even contains Energized Trace Minerals™ for amplified bioavailability.

References (10)
  1. Vitamin B12: MedlinePlus Medical Encyclopedia. 2006. 12 Feb. 2016
  2. Vitamin B12 (Cobalamin) | University of Maryland Medical Center 2013. 12 Feb. 2016
  3. Vitamin B12. Linus Pauling Institute, Oregon State University. Updated 4 Jun 2015. Accessed 20 February.
  4. McBride J. B12 Deficiency May Be More Widespread Than Thought [news release]. 2 Aug 2000. Washington DC, USDA Agricultural Research Service. Accessed 19 Feb 2019.
  5. Vitamin B12 Level: MedlinePlus Medical Encyclopedia. 2006. 12 Feb. 2016
  6. Mayo Clinic Medical Labs. Vitamin B12 Testing. Mayo Clinic Fact Sheet.
  7. Laufer EM, Hartman TJ, Baer DJ, et al. Effects of moderate alcohol consumption on folate and vitamin B(12) status in postmenopausal women. Eur J Clin Nutr. 2004 Nov;58*11):1518-24.
  8. Black, Maureen M. Effects of vitamin B12 and folate deficiency on brain development in children. Food and nutrition bulletin 29.2 suppl1 (2008): S126-S131.
  9. Anemia - B12 deficiency: MedlinePlus Medical Encyclopedia. 2006. 12 Feb. 2016
  10. Patrick J. Skerrett. Vitamin B12 Deficiency Can Be Sneaky, Harmful. Harvard Medical School.

†Results may vary. Information and statements made are for education purposes and are not intended to replace the advice of your doctor. If you have a severe medical condition or health concern, see your physician.


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