Vitamin B12 deficiency: symptoms and testing

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.

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

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.

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The evaluation is a doctor visit, with no membership. Reviewing the results of labs our doctor ordered is a follow-up visit. You pay by card when you request the visit, and you get a full refund if the clinic can’t see you. We do not bill insurance; the lab and the pharmacy charge separately.

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

According to MedlinePlus, a normal blood vitamin B12 level is 299 to 1054 pg/mL, and a result under 299 pg/mL is a possible sign of deficiency. Ranges can vary slightly between labs. To confirm a deficiency, methylmalonic acid is measured: a high level points to a true deficiency.

For the B12 test, MedlinePlus advises not eating or drinking for 6 to 8 hours beforehand. Some medicines, such as metformin and heartburn medicines, can affect the result; don’t stop them on your own. The doctor gives you a lab order with a blood count and explains your result.

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.

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.

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