Conditions
Vitamin B12 deficiency: symptoms, test and treatment
Vitamin B12 deficiency can cause tiredness, pale skin, shortness of breath with effort and, over time, tingling in the hands and feet or balance problems. It is more common after 50, with metformin, with long-term antacids and in diets without animal products. By video, the doctor evaluates you and gives you a lab order. If appropriate, she prescribes treatment and we send it to your pharmacy.
Is it an emergency? Call 911.
Is this an emergency?
This is not an emergency service. Call 911 or go to the nearest emergency room if you have:
- Sudden weakness, numbness or a drooping face on one side, or trouble speaking
- Chest pain or shortness of breath at rest
- Fainting or new confusion
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At a glance
Vitamin B12 deficiency
Common symptoms
- Tiredness, low energy or lightheadedness when you stand up
- Pale skin
- Shortness of breath, mostly with exercise
- A red, swollen tongue or bleeding gums
- Diarrhea or constipation, and poor appetite
- Tingling or numbness in the hands and feet
- Loss of balance
- Trouble concentrating, irritability or confusion
- Other names
- Low B12 · Vitamin B12 deficiency anemia · Pernicious anemia
- Usual test
- Blood count, vitamin B12 level and methylmalonic acid
- Treatment
- Vitamin B12 by mouth or by injection, depending on the cause, only when the medical evaluation calls for it
- Possible complication
- Anemia and nerve damage
On this page(11)
What is vitamin B12 deficiency?
Your body needs vitamin B12 to make red blood cells and to keep your nerves working. It comes from meat, poultry, fish and shellfish, eggs, milk and fortified cereals. To absorb it, your stomach makes a protein called intrinsic factor.
According to MedlinePlus, low B12 happens when you don’t eat enough of it or your body doesn’t absorb it well. If it lasts a long time, it can cause anemia and nerve damage, which can become permanent if it isn’t treated in time.
Who is at higher risk
According to MedlinePlus, deficiency is more common if you:
- Are over 50
- Take metformin long term, a common medicine for type 2 diabetes
- Use antacids or other heartburn medicines long term
- Follow a strict vegetarian or vegan diet
- Have had stomach or intestinal surgery
- Have celiac disease, Crohn’s disease or another digestive problem
- Have pernicious anemia, an autoimmune condition that blocks B12 absorption
- Drink alcohol often
Vitamin B12 deficiency and metformin in Puerto Rico
Many people with diabetes take metformin, and diabetes is very common in Puerto Rico: according to a CDC analysis, 14.4% of adults had diagnosed diabetes in 2021, the highest of any US state or territory. MedlinePlus lists long-term metformin use among the causes of low B12. Don’t stop metformin on your own: if you take it and feel tired or have tingling, the doctor can check your B12 level.
How we help with low B12 by video
You see Dr. Diana Nieves Castro, MD, a Puerto Rico–licensed general practice physician with several years of emergency-department experience, in English or Spanish. She asks about your symptoms, what you eat, your medicines and whether you have had stomach surgery.
We evaluate, diagnose and treat. We give you a lab order for a lab near you: according to MedlinePlus, a blood count and a B12 level are usually checked, with methylmalonic acid to confirm. We go over the results with you in a follow-up visit. If appropriate, the doctor prescribes treatment and we send your prescription to your pharmacy.
We see adults and children of all ages. If the patient is under 21, a parent or legal guardian must be on camera for the whole visit and show photo ID.
Your doctor
Dr. Diana Nieves Castro, MD
General practice physician
Several years of emergency-department experience.
Founding Executive Director of The Health Initiative.
Your visit in 3 steps
Request a visit online 24/7 — we confirm your time by email or text See how our online doctor visit works.
Request your visit.
Book a visit and choose "Doctor visit". You pay by card when you request it.
See the doctor by video.
We send you a secure video link. It works on your phone, tablet or computer.
Get your plan.
You get a lab order. If appropriate, the doctor prescribes and we send your prescription to your pharmacy.
What the visit costs
The evaluation is a US$79 doctor visit, with no membership. Reviewing the results of labs our doctor ordered is a US$49 follow-up visit. You pay by card when you request the visit, and you get a full refund if the visit can’t take place. We do not bill insurance; the lab and the pharmacy charge separately.
Symptoms of low B12
MedlinePlus explains that sometimes there are no symptoms, or they are mild. The most common are:
- Tiredness, low energy or lightheadedness when you stand up
- Pale skin
- Shortness of breath, mostly with exercise
- A red, swollen tongue or bleeding gums
- Diarrhea or constipation, and poor appetite
- Tingling or numbness in the hands and feet
- Loss of balance
- Trouble concentrating, irritability or confusion
Treatment
Treatment depends on the cause. According to MedlinePlus, if B12 is low because of diet, B12 pills may be enough. If your body doesn’t absorb it well, shots are often used, more often at first and then monthly, sometimes for life; some people do well with high doses by mouth. Shots are given in person. The doctor explains which option fits you and, if appropriate, prescribes it.
MedlinePlus notes there is no evidence that B12 supplements prevent or treat dementia or heart disease. B12 corrects a deficiency; it is not an energy shot.
If you are always tired (fatigue) and don’t know why, B12 is just one of the causes the doctor checks.
If you have tingling or balance problems
Nerve damage from low B12 can become permanent if it isn’t treated soon. If you have tingling, numbness, balance or memory problems, get checked soon: the doctor gives you a lab order and, if you need a neurological exam, we refer you for an in-person evaluation.
When to go to the ER
For your safety, call 911 or go to the emergency room if you have:
- Sudden weakness, numbness or a drooping face on one side, or trouble speaking
- Chest pain or shortness of breath at rest
- Fainting or new confusion
How we care for you
We evaluate, diagnose and treat; if needed, we give you a lab order for a lab near you.
We see adults and children of all ages. Patients under 21: a parent with patria potestad (parental authority) or a legal guardian is on camera for the whole visit and shows photo ID.
Real-time video visit. We send you a secure video link. It works on your phone, tablet or computer.
If appropriate, the doctor prescribes and we send your prescription to your pharmacy. We do not prescribe controlled substances.
You must be physically in Puerto Rico during the visit (visitors, tourists and cruise passengers are welcome).
In an emergency, call 911.
Frequently asked questions
What are the symptoms of vitamin B12 deficiency?
Does metformin lower vitamin B12?
What test checks vitamin B12?
Are B12 pills or shots better?
About this page
Author: The Health Initiative
Medical care provided by Dr. Diana Nieves Castro, MD (PR license 24027)
Disclosure: Founding Executive Director of The Health Initiative
Published: 2026-10-02 · Updated: 2026-10-02
Sources (5)
- Vitamin B12 deficiency anemia (MedlinePlus, NIH) (opens in a new tab) (accessed 2026-10-02)
- Vitamin B12 level (MedlinePlus, NIH) (opens in a new tab) (accessed 2026-10-02)
- Vitamin B12 (MedlinePlus, NIH) (opens in a new tab) (accessed 2026-10-02)
- Pernicious anemia (MedlinePlus, NIH) (opens in a new tab) (accessed 2026-10-02)
- CDC, Preventing Chronic Disease 24_0221: prevalence of diagnosed diabetes among adults by state and territory, 2021 (opens in a new tab) (accessed 2026-10-02)