Vitamin B12 Deficiency: Signs, Symptoms, and Treatments

Tired woman reclining on a couch.

Everyday stress can leave you feeling rundown, like you’re muscling through life. Stress can manifest in the body in many ways, but if you’re feeling sluggish and generally unwell, a vitamin deficiency might well be the cause. In short, vitamin deficiencies occur when your body doesn’t have enough said vitamin, which can inhibit certain critical cellular functions.

You’ve probably heard of vitamin B12—the essential vitamin is quite buzzy, especially when it comes to energy levels. But do you really know why B12 is so vital to your health? We asked board-certified internists Arielle Levitan, MD, and Holly Phillips, MD, plus board-certified integrative medicine physician Erika Schwartz, MD, to explain why vitamin B12 is so important, and about the common signs and causes of B12 deficiency. Keep reading for what they had to say.


What Is Vitamin B12?

As their names denote, essential nutrients like B12 help the body perform critical functions. “Vitamin B12 is one of the eight B vitamins. Its medical name is cobalamin,” says Schwartz. She goes on to say it’s something the body doesn’t make on its own; we get B12 solely from foods or supplements. “B12 is found in foods that come from animals, some beans, and is mostly added in processed foods.”

This nutrient has a host of benefits, playing a critical role in cellular metabolism, or the ways in which our body converts energy. “Vitamin B12 is an essential nutrient for our bodies to function,” explains Levitan. Phillips adds the nutrient is essential “in several steps of cell metabolism.” B12 also plays a critical role in nerve and brain health, according to Levitan. Schwartz adds that B12 is important “in central nervous system function, and helps improve cognitive function.”

“Perhaps most importantly, it is critical to the formation of healthy red blood cells,” says Phillips. “If your body doesn’t get enough vitamin B12, you can develop anemia, a condition in which the number of red blood cells is too low or the red blood cells are not able to function properly.”

Ideal amounts vary by demographic. According to Phillips, adults and teens (aged 14-18) should consume 2.4 mcg/day. For kids, the dosage is lower. Schwartz notes that “those who are over the age of 50, pregnant, or lactating require a much higher dosage.”

Signs You Have a Vitamin B12 Deficiency

Since B12 is abundant in animal products like meat, dairy, and fish, our experts agree that people who do not consume these foods, like vegans, are at higher risk for a B12 deficiency. Some common signs and symptoms of B12 deficiency include the following:

You Develop Pernicious Anemia

You might be deficient in B12 if your body isn’t absorbing it correctly. This is common, as Phillips explains, with a certain type of anemia. “Pernicious anemia is an autoimmune condition which damages cells in the stomach that produce a protein called intrinsic factor. Intrinsic factor is needed for the absorption of B12, so if it is too low, B12 levels drop too.”

You Experience Fatigue or General Confusion

According to Levitan, B12 deficiency often “manifests as fatigue, weakness, and trouble with memory and attention.” Although these signs are a bit general, they can serve as a good starting point for addressing a vitamin deficiency. Phillips adds that if you’re feeling “dizzy or lightheaded when standing up from a seated position,” that could be a sign of B12 depletion. She adds that people can also experience difficulty concentrating.

You Experience Nerve Related Symptoms

Levitan notes that because vitamin B12 is critical to proper nerve function, “nerve-related symptoms such as neuropathy (painful burning in feet and hands) or paresthesias (tingling in hands or feet)” can indicate a B12 deficiency.

Causes of Deficiency

As aforementioned, the most common culprit of B12 deficiency is failure to incorporate enough of the nutrient into your diet—especially if you eschew meat, dairy, and fish. “In my practice, I take care of some patients who practice a strict vegan diet in which no animal-based products are consumed at all,” notes Levitan. “Unless they supplement regularly, they can become deficient pretty easily.”

There are, however, other causes that have to do with the body’s inability to absorb B12 properly. Levitan notes that people with GI conditions are particularly prone to B12 deficiencies. “This is typically because GI conditions such as Celiac’s, Crohn’s, colitis, or autoimmune conditions affect the GI tract’s ability to absorb B12,” she explains.

Phillips notes that “after certain gastric bypass surgeries, the area of the intestine which absorbs the vitamin is removed or made smaller.”  Additionally, Levitan says that “aging, leaky gut syndromes, or previous weight-reduction surgery and some genetic and autoimmune disorders” can inhibit the body from properly absorbing nutrients in the gut.

Treatment Options

Treatment of a vitamin B12 deficiency is relatively easy. Of course, daily allowances always vary from person to person, and as such, Schwartz notes that “recommended doses vary” and a physician’s consult is recommended to address specific treatment options.

Dietary Supplementation

If you don’t want to modify your diet to include B12 rich foods, you’ll have to address the deficiency with a supplement. “Most people can take B12 as part of a personalized daily vitamin,” explains Levitan. “Their dose is determined by their individual needs. A very small minority of people can’t absorb B12 in pill form and need to take it through another delivery system.” She explains that there are sublingual and nasal forms, as well as injections.

B12 Injections

Schwartz is a proponent of B12 injections, especially in order to correct a true deficiency. “B12 injections consist of an intramuscular injection of vitamin B12 of various dosing based on patient needs and processing capacity. I do recommend this method and use it to treat my own patients. [This method] bypasses any absorption incompetencies in the gut and leads to a much greater bioavailability of the pure vitamin B12. The absorption of oral B12 supplements is very low.”

Levitan notes that a physician’s care is critical when undergoing this method. “This is only done under the supervision of a physician if you have failed other forms of supplementation and typically involves monthly injections,” she explains.

You may have heard that people administer B12 injections for boosts of energy, and because fatigue is one of the common symptoms of a B12 deficiency, this seems like a reasonable thing to do. Unfortunately, according to Phillips, this is not supported by medical research. “There are people who believe the injections provide an energy boost even for people who are not deficient in vitamin B12. Overall, there is not enough data to support the benefit of administering the injections to raise B12 levels above the target range.”

The Final Takeaway

Bottom line: Addressing B12 deficiency with as little intervention as possible is easy to do with dietary changes. “The best source of all nutrients is food,” says Phillips. If the deficiency is related to the body’s inability to absorb B12, an indication must be made by a physician. Further treatment plans, including intramuscular injections, will be necessary.


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