B12 Deficiency: Symptoms, Who Is Low, and the Two Tests
The symptoms of B12 deficiency include numb or tingling hands and feet, unsteady walking, tiredness, pale skin, a sore smooth tongue and memory problems (NIH). About 3.6% of US adults are low (NIH), and two blood tests confirm it. Numbness and tingling are often the first sign.
If you have tingling, numbness, balance trouble or memory problems, see a doctor soon and ask for a B12 blood test. Nerve damage from low B12 is easiest to undo when it is caught early.
General information, not a diagnosis.
Signs of low B12, and which come first
Low B12 can cause any of these signs (NIH). None of them proves it on its own.
- Tingling or numbness in the feet and hands. When low B12 affects the nerves, this or poor balance is usually the first sign (Healton 1991).
- Unsteady walking or poor balance. It means more when it comes with numb feet.
- Tiredness and weakness. Very common, but so many things cause it that it says little alone.
- Pale skin or a pounding heart. These come from anemia (too few healthy red blood cells).
- A sore, smooth tongue. Low iron or low folate can cause it too.
- Memory loss or confusion. Easy to blame on age, so it is often missed.
- Weight loss. Losing weight without trying is on NIH’s list too.
A normal blood count does not rule it out
Nerve signs can come before anemia. In a study of 141 people with nerve or memory problems from low B12, about 1 in 4 had no anemia (Lindenbaum 1988).
Who is most likely to be low
Counting borderline levels, about 12.5% of US adults are low (NIH). Adults over 60 are about the same on that test, but about 1 in 5 has at least one abnormal B12 result (NIH). The risk jumps in three groups:
- Vegans and vegetarians. Only animal foods have B12 naturally. In a UK study of men, 52% of vegans were low, against 7% of vegetarians (Gilsing 2010). See B12 for vegans.
- People on certain medicines. Metformin is the clearest case: in a 4-year trial, 7 more people in 100 became deficient than on placebo (de Jager 2010). Years of acid reducers, colchicine, some seizure medicines and nitrous oxide used for fun are also linked (NICE 2024). Do not stop a medicine on your own.
- People who absorb B12 poorly. Pernicious anemia is an immune condition that stops the stomach making the protein B12 needs to get in. About 151 in 100,000 people in the US have it (NIH). After weight-loss surgery, about 8.5% are low five years or more later (Chen 2024). Celiac disease and low stomach acid with age also get in the way. See B12 for seniors.
If you are in one of these groups, ask your doctor about a B12 test.
The two tests: blood B12 first, then MMA
The first test measures the B12 in your blood. The lab report gives it in pg/mL (picograms per milliliter). Under 200 is low, and 200 to 300 is borderline (NIH). Your lab’s own range has the final say.
If your level is borderline, the second test is MMA (methylmalonic acid). MMA builds up in the blood when your cells are short of B12, so a high MMA confirms it (NIH). Weak kidneys can raise it too.
Have your blood drawn before you start B12 pills. Pills raise the level quickly, so a later test may not show the shortage. If strong signs and a normal-looking number disagree, UK blood experts advise starting treatment anyway.
If you take high-dose folic acid, tell your doctor. Folic acid can fix the anemia while nerve damage from low B12 goes on.
More in the MMA test: normal range and what else raises it.
How low B12 is treated: pills or shots
Shots are the usual treatment for severe deficiency and nerve symptoms, because they skip the gut (NIH). If pernicious anemia is the cause, UK guidance advises shots for life (NICE 2024). The same goes after the whole stomach is removed. After some weight-loss operations, your team may choose shots over pills.
For other causes, a daily pill can work. In small trials, 1,000 to 2,000 mcg by mouth raised blood levels about as much as shots did, though the evidence is weak (Wang 2018). Follow your doctor’s plan.
Blood counts recover faster than nerves. In one large study of nerve cases, every treated patient got better and about half recovered fully.
If your doctor says to take a B12 pill
Your doctor sets the dose. For a daily pill, 1,000 mcg is the usual size: about 1 in 3 of the 203 B12 labels we read hold exactly that.
NatureWise Vitamin B12 1000 mcg
$0.12 a day. Our pick: on NSF’s testing list and the cheapest tested pill. The softgel contains gelatin.
Nature Made Vitamin B12 1000 mcg Fast Dissolve
$0.20 a day. A small tablet that dissolves in your mouth. On USP’s testing list.
Vegan? Neither of these says vegan. B12 for vegans lists pills that do.
Frequently asked questions
Can babies get B12 deficiency?
Yes. A baby fed only breast milk by a mother who eats no animal foods can run low early in life. The mother’s own low B12 may be mild and go unnoticed. Untreated, it can harm growth and development (NIH). Vegan mothers should take B12 and ask the baby’s doctor about it.
Can low B12 cause depression or anxiety?
It can play a part. Studies of people with nerve problems from low B12 found mood changes and, rarely, psychosis. Mood changes have many other causes too, so low B12 is only one thing to rule out.
Will a B12 pill fix my tiredness?
Only if you are low. If your B12 is normal, more has not been shown to add energy. More in B12 and energy.
Related guides
- The MMA test: the second test, its normal range and what else raises it
- B12 for seniors: why low B12 is more common after 60
- B12 for vegans and vegetarians: how to get enough with no meat
- B12 dosage guide: how much a day, by age
- B12 and energy: when it helps tiredness and when it does not
- Iron: another common cause of anemia
Sources
- NIH Office of Dietary Supplements. "Vitamin B12: Fact Sheet for Health Professionals" (symptoms, test cut-offs, MMA, how common low B12 is, pernicious anemia, babies of vegan mothers, shots). ods.od.nih.gov (updated July 2, 2025; read October 15, 2026).
- Healton EB, et al. (nerve signs first in most cases; recovery after treatment) "Neurologic aspects of cobalamin deficiency." Medicine (Baltimore). 1991. PMID: 1648656
- Lindenbaum J, et al. "Neuropsychiatric disorders caused by cobalamin deficiency in the absence of anemia or macrocytosis." N Engl J Med. 1988. PMID: 3374544
- Gilsing AM, et al. "Serum concentrations of vitamin B12 and folate in British male omnivores, vegetarians and vegans..." Eur J Clin Nutr. 2010. PMID: 20648045
- de Jager J, et al. "Long term treatment with metformin in patients with type 2 diabetes and risk of vitamin B-12 deficiency." BMJ. 2010. PMID: 20488910
- Lam JR, et al. (acid reducers) "Proton pump inhibitor and histamine 2 receptor antagonist use and vitamin B12 deficiency." JAMA. 2013. PMID: 24327038
- Chen L, et al. "Long-term prevalence of vitamin deficiencies after bariatric surgery: a meta-analysis." Langenbecks Arch Surg. 2024. PMID: 39030449
- Devalia V, et al. (British Society for Haematology: treat when strong signs and the test disagree) "Guidelines for the diagnosis and treatment of cobalamin and folate disorders." Br J Haematol. 2014. PMID: 24942828
- Miller JW, et al. (folic acid and hidden B12 deficiency) "Excess Folic Acid and Vitamin B12 Deficiency: Clinical Implications?" Food Nutr Bull. 2024. PMID: 38987872
- Wang H, et al. "Oral vitamin B12 versus intramuscular vitamin B12 for vitamin B12 deficiency." Cochrane Database Syst Rev. 2018. PMID: 29543316
- NICE. Vitamin B12 deficiency in over 16s: diagnosis and management (NG239), 2024 (medicines, nitrous oxide, shots for pernicious anemia and after stomach surgery; read October 16, 2026).
- Prices are each brand’s list price, checked October 15, 2026. Amazon’s price may differ.