Symptoms of vitamin B12, or folate, deficiency can include fatigue, lethargy, low mood, shortness of breath, and nerve problems. Treatment often involves dietary changes or vitamin B12 supplements.

The human body does not create vitamin B12, so people must get this nutrient from their diet. It is present in animal-based foods, such as red meat, poultry, eggs, dairy, and fish. Vegetarian and vegan sources of B12 can include fortified cereals, plant milks, bread, and nutritional yeast.

Vitamin B12 is crucial for making DNA and red blood cells (RBCs) and supporting the nervous system.

Many of the symptoms of vitamin B12 deficiency arise because it causes a lack of healthy blood cells. The body needs plenty of these cells to get oxygen around the body and keep the organs in good health. Vitamin B12 also plays a vital role in allowing the brain and nerves to work properly.

In this article, we explore 11 symptoms of vitamin B12 deficiency and explain why they occur.

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Vitamin B12 deficiency may cause “pins and needles” in the hands or feet. This symptom occurs because the vitamin plays a crucial role in the nervous system. Its absence can cause people to develop nerve conduction problems or nerve damage.

In the nervous system, vitamin B12 helps produce a substance called myelin that shields the nerves and helps them transmit sensations. Without sufficient myelin, nerves are more prone to damage.

Problems are more common in the nerves in the hands and feet, which are called peripheral nerves. Peripheral nerve damage may lead to tingling in these parts of the body.

Over time, peripheral nerve damage can lead to movement problems. Numbness in the feet and limbs may make it hard for a person to walk without support. They may also experience muscle weakness and diminished reflexes.

A vitamin B12 deficiency can lead to pale skin and yellowing of the skin, called jaundice. These changes in skin color can develop when a person’s body is unable to produce enough RBCs.

Without enough RBCs, the skin may look pale. Vitamin B12 plays a role in the production of red blood cells. A vitamin B12 deficiency can cause a lack of RBCs, or megaloblastic anemia, which has an association with jaundice.

This type of anemia can also weaken RBCs, which the body then breaks down more quickly. When the liver breaks down RBCs, it releases bilirubin. Bilirubin is a brownish substance that gives the skin the yellowish tone that is characteristic of jaundice.

Megaloblastic anemia due to vitamin B12 deficiency may lead to a person feeling fatigued. Without enough RBCs to carry oxygen around their body, a person can feel extremely tired.

A fast heart rate may be a symptom of vitamin B12 deficiency. The heart may start to beat faster to make up for the reduced number of RBCs in the body. This response is the body’s way of trying to ensure that enough oxygen circulates through all of the body’s systems and reaches all the organs.

Anemia that results from a vitamin B12 deficiency may also cause a person to feel short of breath. This relates to a lack of RBCs and a fast heartbeat.

Anyone who is experiencing real difficulty breathing should see a doctor straight away.

A vitamin B12 deficiency can affect oral health and cause the following mouth problems:

  • glossitis, which causes a swollen, smooth, red tongue
  • bad taste in the mouth
  • a burning sensation in the mouth

These symptoms occur due to a reduction in RBC production, which results in less oxygen reaching the tongue.

Vitamin B12 deficiency may cause problems with thinking, which doctors refer to as cognitive impairment. These issues include difficulty thinking or reasoning and memory loss.

Some evidence suggests a link between low vitamin B12 levels to a higher risk of dementia, Alzheimer’s disease, and Parkinson’s disease.

The reduced amount of oxygen reaching the brain might be to blame for the thinking and reasoning problems.

Being deficient in vitamin B12 can affect a person’s mood and may lead to mental health problems.

For example, a 2020 review notes a link between vitamin B12 deficiency and depression, suggesting low levels increase the risk of developing depression.

Vitamin B12 deficiency can affect the digestive tract.

A lack of RBCs means that not enough oxygen reaches the gut. Insufficient oxygen here may lead to a person both feeling and being sick. It may also cause diarrhea.

As a result of digestive problems, such as nausea, people with vitamin B12 deficiency may lose their appetite. A decreased appetite can lead to weight loss in the long term.

Even if a person gets enough vitamin B12 in their diet, some underlying health conditions can affect the absorption of vitamin B12 in the gut. These conditions can include:

Other factors that may lead to a vitamin B12 deficiency can include drinking excessive amounts of alcohol or using certain drugs, such as some heartburn medicines and metformin.

The following are more likely to have a vitamin B12 deficiency:

  • being older, because a person becomes less able to absorb B12 as they age
  • eating a vegetarian or vegan diet
  • taking anti-acid medication for an extended period
  • weight loss surgery or other stomach surgery, which can affect how the digestive system absorbs vitamin B12

Most people can get enough vitamin B12 from dietary sources. For those who cannot, a doctor may prescribe or recommend B12 supplements.

People can take B12 supplements in the form of oral tablets, sublingual tablets that dissolve under the tongue, or injections. A doctor can provide advice on the correct dosage of this vitamin.

People who have trouble absorbing vitamin B12 may need shots of the vitamin to treat their deficiency.

A doctor can advise people on the best way to prevent vitamin B12 deficiency, depending on their dietary choices and health.

Read on to learn more about vitamin B12 food sources, including vegan and vegetarian options.

Some frequently asked questions about vitamin B12 deficiency may include:

What happens when vitamin B12 is low?

Vitamin B12 is important for producing RBCs and supporting the nervous system. As such, low B12 levels can cause low oxygen levels and nerve problems.

What are the signs of low vitamin B12?

In most people, the most common signs of a vitamin B12 deficiency may include fatigue, lethargy, pins and needles in the hands and feet, oral problems, confusion, and irritability.

What is the fastest way to fix B12 deficiency?

The quickest way to treat a vitamin B12 deficiency will involve altering dietary plans to include more B12 or taking B12 supplements.

What does B12 fatigue feel like?

A vitamin B12 deficiency can cause a person to experience extreme tiredness, lack of energy, breathlessness, and feeling faint.

Fatigue, lethargy, low mood, shortness of breath, and nerve problems can all be symptoms of vitamin B12, or folate, deficiency. Many of these symptoms happen because vitamin B12 deficiency causes a lack of healthy blood cells.

Treatment often involves dietary changes or vitamin B12 supplements.