Deep inside your body, vitamin B12 — aka cobalamin — performs essential tasks like maintaining the health of your red blood cells and creating DNA, according to the National Institutes of Health (NIH).
Our bodies don't naturally make this nutrient, but because many animal-based foods (think: meat, milk, eggs) are high in vitamin B12, most of us get all we need through our diet, according to the NIH.
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Some people can fall short, though, including:
- Vegetarians and vegans: "Plant foods do not have B12 unless they are fortified," says Amber Ingram, RD, a registered dietitian at The Ohio State University Wexner Medical Center. If you fall short on this vitamin due to following a plant-based diet, try taking a multivitamin or B12 supplement or seek out B12-fortified foods.
- Older adults: Up to 43 percent are deficient in B12, according to the NIH — that's due to not having enough of a certain stomach acid responsible for separating vitamin B12 from protein.
- People who can't absorb vitamin B12 properly: Insufficient stomach acid can also be a problem for people who take acid reflux medications or have certain diseases, such as chronic or atrophic gastritis, celiac or Crohn's disease, Ingram says. People with pancreatitis also may not be able to absorb B12 properly. Finally, some people do not have sufficient amounts of intrinsic factor, a protein that enables your body to absorb vitamin B12. Anyone with the autoimmune disease pernicious anemia cannot make intrinsic factor at all.
- Those with kidney issues: People with chronic kidney disease are at a higher risk for nutritional deficiencies including B12 because of medication interactions, dietary restrictions and malnutrition, according to a January 2020 study in International Journal of Advances in Medicine. Dialysis may also cause a loss of B12.
A deficiency in vitamin B12 tends to creep up on people: "Your body usually stores enough B12 that a deficiency would not occur for a few years," Ingram says.
Blood tests can reveal if you have a vitamin B12 deficiency. A normal result will fall between 160 to 950 picograms per milliliter (pg/mL), according to the Icahn School of Medicine at Mount Sinai. Below 160 indicates a possible deficiency.
A methylmalonic acid (MMA) test may also be used. This measures the amount of MMA in the blood or urine, and a higher than normal number usually indicates B12 deficiency, according to the National Library of Medicine. However, a high reading may also be due to renal failure, Ingram says.
The symptoms of low vitamin B12 or a vitamin B12 deficiency aren't always very noticeable. But don't disregard them: Left untreated, a vitamin B12 deficiency can lead to permanent damage to your nervous system, according to the American Academy of Family Physicians (AAFP).
Here's a look at some of the common signs of a vitamin B12 deficiency.
How Much Vitamin B12 Do You Need?
Adults need 2.4 micrograms (μg) of B12 per day, per the NIH. People who are pregnant or breastfeeding require slightly higher amounts.
1. Fatigue or Weakness
When you are low on vitamin B12, you may develop vitamin B12 deficiency anemia, aka megaloblastic anemia, according to Johns Hopkins Medicine. With anemia, your body doesn't make enough red blood cells. (The more common type of anemia, iron-deficiency anemia, produces some of the same symptoms but is not connected to vitamin B12 deficiency.)
This will leave you feeling weak and tired, Ingram says. That's because red blood cells are vital to distributing oxygen around your body — like to your tissue and organs — and when they aren't healthy, they can't fulfill that responsibility properly.
2. Dizziness or Shortness of Breath
Feeling tired isn't the only symptom of low levels of B12 and unhealthy blood cells. Lack of oxygen in the body from low red blood cell count can also cause dizziness and shortness of breath, Ingram says.
Dizziness can also take on the uncomfortable sensation that you or the space around you is rotating, which is known as vertigo, per the Mayo Clinic. You may also feel lightheaded with a vitamin B12 deficiency, according to HealthLink BC.
3. Heart Rate Changes
A rapid heart rate is a symptom of a vitamin B12 deficiency, according to the University of Rochester Medical Center.
Ingram notes that heart palpitations, or a feeling that the heart is fluttering or skipping beats, can also be a sign of low oxygen in the body due to inadequate amounts of B12.
4. Pale or Yellow Skin
This is a common symptom of a vitamin B12 deficiency, according to the Mayo Clinic.
Ingram notes that paleness can be the result of a low red blood cell count.
5. Numbness or Tingling
Vitamin B12 helps maintain healthy nerve cells. If those cells aren't receiving the nutrients they need, an early sign may be numbness or a tingling sensation in your fingers or toes, according to Johns Hopkins Medicine.
"B12 deficiency can cause damage to the nervous system," Ingram confirms, noting that neurologic symptoms may include a "pins and needles" feeling in your extremities and issues with balance (more on that later).
Similarly, burning feet syndrome — an uncomfortable sensation where your feet feel hot— can occur due to vitamin deficiencies and malabsorption, per the Cleveland Clinic.
Because B12 is so essential in keeping your nervous system healthy, a deficiency may cause tremors or uncontrollable shaking in some people, per a December 2014 study in Neurological Research.
7. Confusion or Trouble Focusing
Feeling fuzzy or forgetful is another common sign of too-low B12 levels, according to Harvard Health Publishing. Some people experience memory loss, and others have trouble with thinking and reasoning.
Delirium, dementia and paranoia are symptoms of an advanced vitamin B12 deficiency, according to the Merck Manual.
When you have a deficiency, taking vitamin B12 supplements can improve memory, but supplementing when there isn't a deficiency doesn't ease this symptom for people with Alzheimer's disease or dementia, according to the Mayo Clinic.
8. Difficulty Walking or Balancing
If ordinary activities like walking become challenging, a vitamin B12 deficiency could be responsible, Ingram says.
Loss of balance is another symptom of the nerve damage that accompanies this deficiency, according to Mount Sinai.
9. Swollen or Sore Tongue
Vitamin B12 deficiency can cause issues in the mouth, too. In particular, it may cause the tongue to swell and feel sore, per the NIH.
The tongue may also appear "beefy red," according to Stanford Medicine — and glossitis (when the tongue is swollen and inflamed) can make it appear smooth.
10. Changes to Your Appetite and Digestive Health
A loss of appetite and even weight loss are common signs of low vitamin B12, according to the NIH. And it can also change your bowel movements: Diarrhea and constipation can also be symptoms, according to Mount Sinai.
You may also experience other GI-type issues, such as nausea, vomiting and bloating, according to the National Heart, Lung and Blood Institute.
A B12 deficiency could also lead to urinary incontinence, according to PeaceHealth.
IBS and B12 Deficiency: Is There a Connection?
One of the most common symptoms of IBS is alternating between bouts of diarrhea and constipation, according to the Mayo Clinic. Other symptoms include cramping and bloating, difficulty swallowing and weight loss.
While some of the symptoms of the two conditions are the same, "there is no scientific evidence that IBS and vitamin B12 deficiency are connected in any way," says Marta Ferraz Valles, RDN, a dietitian at the Institute for Digestive Health and Liver Disease at Mercy Medical Center in Baltimore.
Still, Niket Sonpal, MD, a New York-based internist and gastroenterologist, says it's not uncommon for people with IBS to also have a vitamin B12 deficiency. "Due to their disrupted intestinal walls, it is difficult for the vitamin to be absorbed in the small intestine," he explains.
11. Increased Risk of Infection Due to Neutropenia
Vitamin B12 deficiencies can also lead to neutropenia, which is when you're low on a type of white blood cell called neutrophils, according to the Cleveland Clinic. This condition is a common side effect of cancer treatment.
As with other white blood cells, neutrophils are active in fighting infection, according to the Cleveland Clinic. Neutropenia therefore results in increased susceptibility to infection.
If neutropenia is caused by low levels of vitamin B12 — or other micronutrients, such as folate and copper — treatment may involve replenishing the nutrients. This may involve taking supplements. If you are unable to absorb vitamin B12, your health care provider may recommend a vitamin B12 injection, according to the Cleveland Clinic.
12. Vision Changes
Eye-related issues aren't a frequent symptom of a vitamin B12 deficiency, according to a December 2020 systematic review in the Annals of Medicine and Surgery.
Some people, however, experience optic atrophy, or damage to the optic nerve due to a B12 deficiency. This can lead to blurry or less-sharp vision, abnormal color vision or difficulty with peripheral vision, according to the Cleveland Clinic.
These vision-related symptoms are treated with vitamin B12 replacement, according to the systematic review.
13. Hair Loss
Because vitamin B12 is so important for the health of cells, it's not surprising that a deficiency in this vitamin is "associated with hair loss," per a December 2018 review of the role of vitamins and minerals in hair loss in Dermatology and Therapy.
But as the review authors point out, there hasn't been a lot of research into the relationship — so it's hard to pin down how exactly a B12 deficiency is linked to hair loss.
More research is needed to understand the connection, and it's worth noting the review authors do not recommend vitamin B12 supplements as a treatment tactic for hair loss. A different B vitamin — biotin — is commonly prescribed for people with hair loss, per the Cleveland Clinic.
14. Skin and Nail Changes
While it's rare, a vitamin B12 deficiency can cause changes to your skin and nails.
"An often-forgotten link" is the subheading of an April 2008 study in Canadian Family Physician that describes two patients whose only symptom of their vitamin B12 deficiency was skin lesions. With one patient, doctors initially suspected she had dermatitis — aka skin irritation, which can lead to a skin rash or itchy skin — before diagnosing the B12 deficiency.
This is an older study, but more recent research around this link is very limited.
Fingernail changes are another very uncommon symptom that could point to vitamin B12 deficiency, according to a March 2018 article in BMJ Case Reports. Nails may appear blue or black in color.
A March 2020 case study in JAAD Case Reports about a man who experienced black hyperpigmentation in the nails on his hands and feet describes this as "a rare manifestation of vitamin B12 deficiency."
A rare issue you may experience due to vitamin B12 deficiency is edema, or swelling of the feet and ankles. A January 2020 case study in the Journal of Maine Medical Center describes a man with vitamin B12 deficiency (and other vitamin deficiencies) who experienced edema.
A similar case study was published February 2016 in the IOSR Journal of Dental and Medical Sciences: Here, the patient — a vegetarian — had edema in both legs that cleared up after supplementation with vitamin B12.
This sensation is similar to feet swelling in hot weather, also known as heat edema, but it'll be long-lasting if due to a vitamin deficiency.
Other Symptoms Possibly Associated With Vitamin B12 Deficiency
Other symptoms and health conditions associated with a vitamin B12 deficiency are less clear-cut. You may have heard the following symptoms could be related to B12, but there's little, if any, evidence to support these claims.
For example, it's difficult to unpack vitamin B12's role when it comes to insomnia. People with depression often experience difficulty sleeping, and a shortage of this vitamin is associated with depression, according to a September 2019 study in the Open Access Macedonian Journal of Medical Sciences.
But that's not to say a B12 deficiency causes insomnia: "The direct relationship between insomnia and vitamin B12 levels is yet to be established," the study authors note. More research is needed in this area to determine how vitamin B12 affects sleep — and if taking the vitamin can end insomnia.
It's also possible a vitamin B12 deficiency is associated with elevated cholesterol, according to a February 2015 study in Clinical Epigenetics. More research is needed to understand the association, though.
A June 2017 case study in Internal Medicine highlights a 72-year-old person with type 1 diabetes whose impaired awareness of hypoglycemia improved after four weeks of vitamin B12 supplementation. (Impaired awareness of hypoglycemia means you're not able to recognize the early warning signs of low blood sugar.)
The researchers call for recognizing vitamin B12 deficiency as one of the causes of impaired awareness of hypoglycemia, but this hasn't been widely accepted and requires more research.
A variety of symptoms — from common to rare — can occur when vitamin B12 levels fall short. But some of these symptoms are vague and common with many other conditions and diseases (think: fatigue and weakness, or feeling forgetful).
That's why it's best to see a doctor or registered dietitian before self-diagnosing a deficiency. "Have them draw some labs for you to determine if your symptoms are in fact B12 deficiency or related to something else," Ingram says.
Treatment options may be as simple as adjusting your diet or adding supplements. But other more involved strategies might be required.
"A severe B12 depletion is not going to be fixed with only adding more B12-rich foods to the diet," Ingram says. Instead, your health care team will need to create a treatment plan based on what will work best for you.
- National Institutes of Health: "Vitamin B12"
- Icahn School of Medicine at Mount Sinai: "Vitamin B12 level"
- American Academy of Family Physicians: "Vitamin B12"
- Johns Hopskins Medicine: "Vitamin B12 Deficiency Anemia"
- Mayo Clinic: "Vitamin deficiency anemia"
- Mayo Clinic: "Dizziness"
- HealthLink BC: "Vitamin B12 Deficiency Anemia"
- University of Rochester Medical Center: "Vitamin B-12 Deficiency Anemia"
- Neurological Research: "Involuntary movements due to vitamin B12 deficiency"
- Cleveland Clinic: "Burning Feet Syndrome (Grierson-Gopalan Syndrome)"
- Journal of Maine Medical Center: "Fresh Fruits and V ruits and Vegetables Really Do K egetables Really Do Keep the Doct eep the Doctor Away: Symptomatic Vitamin Deficiency in a Middle Aged Man "
- IOSR Journal of Dental and Medical Sciences: "Vitamin B-12 deficiency presenting as bilateral pedal edema; Physiological role of vitamin B-12 in maintenance of vascular smooth muscle tone"
- Harvard Health Publishing: "Vitamin B12 deficiency can be sneaky, harmful"
- Merck Manual: "Vitamin B12 Deficiency"
- Mayo Clinic: "Vitamin B-12: Can it improve memory in Alzheimer's?"
- Mount Sinai: "Vitamin B12 deficiency anemia"
- Stanford Medicine: "Technique of the Tongue Exam"
- National Heart, Lung and Blood Institute: "Pernicious Anemia"
- PeaceHealth: "Urinary Incontinence (Holistic)"
- UK National Health Service: "Vitamin B12 or folate deficiency anaemia"
- Cleveland Clinic: "Neutropenia"
- Annals of Medicine and Surgery: "Optic neuropathy as a presenting feature of vitamin B-12 deficiency: A systematic review of literature and a case report"
- Cleveland Clinic: "Optic Atrophy"
- Dermatology and Therapy: "The Role of Vitamins and Minerals in Hair Loss: A Review"
- Cleveland Clinic: "Is Biotin as Good as Advertised for Your Hair Loss?"
- Canadian Family Physician: "Cutaneous lesions and vitamin B12 deficiency"
- Cleveland Clinic: "Do You Bruise Easily? When to Get It Checked Out"
- BMJ Case Reports: "Blue nails: window to micronutrient deficiency"
- JAAD Case Reports: "Total melanonychia of 20 nails as a rare manifestation of vitamin B12 deficiency"
- Open Access Macedonian Journal of Medical Sciences: "The Effects of Magnesium – Melatonin - Vit B Complex Supplementation in Treatment of Insomnia"
- Clinical Epigenetics: "Vitamin B12 insufficiency induces cholesterol biosynthesis by limiting s-adenosylmethionine and modulating the methylation of SREBF1 and LDLR genes"
- International Journal of Advances in Medicine: "Study of vitamin B12 deficiency in chronic kidney disease"
- Internal Medicine: "An Impaired Awareness of Hypoglycemia Improved After Vitamin B12 Treatment in a Type 1 Diabetic Patient"
- NLM: "Methylmalonic Acid (MMA) Test"