Vitamin B12 is an essential nutrient that your body needs for processes like DNA synthesis, energy production, and central nervous system function (1Trusted Source).

Studies suggest that up to 20% of people over the age of 60 in the United States and the United Kingdom are deficient in the vitamin. This is often due to limited dietary intake, malabsorption, medical conditions, or the use of B12-depleting medications (2Trusted Source, 3Trusted Source, 4Trusted Source, 5Trusted Source).

Vitamin B12 deficiency is determined as follows (2Trusted Source):

Because the ability to absorb B12 from food declines with age, deficiency is more common in older adults. Still, that doesn’t mean children and younger adults, including those who are pregnant and nursing, can’t develop B12 deficiency (5Trusted Source, 6Trusted Source).

B12 deficiency is often misdiagnosed, often due to inadequate laboratory testing or because the symptoms are not specific (7Trusted Source).

So what happens when your vitamin B12 is low? Read on about nine of the most commonly reported symptoms related to B12 deficiency and how this deficiency is diagnosed and treated.

If you’re low or deficient in B12, you’ll likely feel fatigued.

Your body’s cells need B12 to function properly. As such, having inadequate B12 levels can decrease normal red blood cell production, which can impair oxygen delivery (8Trusted Source).

Specifically, a deficiency in B12 can cause megaloblastic anemia. This condition leads to the formation of large, abnormal, and immature red blood cells and impaired DNA synthesis (2Trusted Source, 9Trusted Source).

Like the condition called iron deficiency anemia, anemia related to B12 deficiency may make your skin pale due to a lack of fully-matured, healthy red blood cells in the body (2Trusted Source).

B12 deficiency can also cause a condition called jaundice, which makes your skin and the whites of your eyes take on a yellowish color due to high levels of bilirubin (2Trusted Source).

Headaches are among the most commonly reported symptoms related to B12 deficiency in both adults and kids (2Trusted Source, 10Trusted Source, 11Trusted Source).

A 2019 study with 140 people, half of whom experienced migraine, found that blood levels of B12 were significantly lower in the participants with migraine (12Trusted Source). Those with the highest B12 levels were 80% less likely to have migraine compared with participants with the lowest B12 levels (12Trusted Source).

Research continues to investigate if treatment with B12 may improve migraine headache symptoms in some people (13Trusted Source).

B12 deficiency is associated with a greater risk of developing depression (14Trusted Source, 15Trusted Source).

Having low levels of B12 can cause elevated levels of a sulfur-containing amino acid called homocysteine. In turn, this may contribute to the development of depression by increasing oxidative stress, DNA damage, and cell death in the body (16Trusted Source, 17Trusted Source).

A 2020 study with 132 children and teens, 89 with and 43 without depression, found that the participants with depression had lower B12 levels and higher levels of homocysteine compared with those without depression (17Trusted Source).

In addition to depressive symptoms, low or deficient B12 levels may lead to other mental conditions, including psychosis and mood disorders (18Trusted Source).

A B12 deficiency may also cause diarrhea, nausea, constipation, bloating, gas, and other gastrointestinal symptoms (2Trusted Source, 19Trusted Source).

These issues can affect both adults and children (2Trusted Source, 20Trusted Source).

Because a deficiency in B12 negatively impacts the central nervous system, people with low or deficient B12 levels may feel foggy-headed and have difficulty concentrating and completing tasks (21Trusted Source).

Many studies have associated low B12 levels with worsened mental function in older adults (22Trusted Source, 23Trusted Source).

Fortunately, studies show that mental impairment related to low B12 levels can improve with B12 treatment.

For example, a 2020 study gave 202 people with mild mental impairment and low or low-normal B12 levels and elevated homocysteine levels B12 replacement therapy for 3 months (21Trusted Source).

After the treatment, 84% of the participants reported significant improvements in symptoms, like poor focus, memory decline, and forgetfulness (21Trusted Source).

Glossitis is a medical term that refers to an inflamed, red, and painful tongue. It can be caused by a B12 deficiency (24Trusted Source).

In people with this deficiency, glossitis can appear alongside stomatitis, which is characterized by sores and inflammation in the mouth (25Trusted Source).

Even though glossitis and stomatitis are common in people with B12 deficiency-related anemia, they can also occur without anemia and can be a sign of an early B12 deficiency (25Trusted Source). That being said, glossitis can also have other causes (25Trusted Source).

Many adults and kids who have B12 deficiency report experiencing paresthesia, a burning or pins-and-needles sensation in certain areas of the body like the hands and feet. (7Trusted Source, 20Trusted Source).

Unfortunately, this symptom of B12 deficiency overlaps with symptoms related to diabetic neuropathy — nerve damage caused by high blood sugar that can cause pain and numbness in the extremities (26Trusted Source).

People with diabetes taking metformin are at a higher risk of developing B12 deficiency because this medication can reduce vitamin B12 absorption in the body (4Trusted Source).

So, a B12 deficiency could be misdiagnosed as peripheral neuropathy in people with diabetes.

As a result, many experts recommend that people taking metformin regularly get screened for vitamin B12 deficiency.

In addition to the symptoms above, B12 deficiency may lead to the following:

• Muscle cramps and muscle weakness: B12 deficiency negatively impacts motor and sensory nerve function, which can cause muscle cramps and weakness (7Trusted Source, 27Trusted Source).
• Impaired coordination: Ataxia, or impaired balance and coordination, is a neurological symptom that can be caused by B12 deficiency. As such, a person with B12 deficiency may have difficulty walking and balancing (2Trusted Source).
• Erectile dysfunction: Men with B12 deficiency may experience erectile dysfunction as a result of increased levels of homocysteine in the body (28Trusted Source).
• Vision disturbances: B12 deficiency may cause vision disturbances, possibly due to damage to the optic nerve (29Trusted Source)

Because vitamin B12 deficiency symptoms aren’t specific to the condition, it may go undetected or get misdiagnosed.

If you’re experiencing any of the symptoms listed above, it’s important to discuss them with a healthcare professional.

This is especially relevant if you:

• follow a restrictive diet, like a vegan diet
• are over the age of 60
• are pregnant or nursing
• have a medical condition that can deplete B12 levels
• take a B12-depleting medication, like metformin or proton pump inhibitors

In addition to learning about your symptoms and giving you a physical exam, a healthcare professional can rule out a B12 deficiency by ordering various blood tests(2Trusted Source).

If you’re diagnosed with too low B12 levels, your healthcare professional will recommend the most appropriate treatment.

Learn more on vitamin B12 deficiency treatment.

What is the fastest way to fix B12 deficiency?

Treatment of B12 deficiency typically includes oral supplements or injections.

What is the most common cause of B12 deficiency?

Typically vitamin B12 deficiency develops because you’re not getting eating enough B12-rich foods like fish and shellfish, organ meats, and eggs.

For example, this is common among people who follow a vegan diet. In addition, certain medical conditions and medications can cause vitamin B12 deficiency (30).

Learn more about the causes of vitamin B12 deficiency.

Can vitamin B12 deficiency be a sign of cancer?

While it isn’t a sign of cancer, vitamin B12 deficiency does raise your chance of getting different types of cancer (31Trusted Source).

B12 deficiency can cause a variety of symptoms, including fatigue, headaches, depression, pale or yellow skin, mental impairment, and pain and inflammation in the mouth and tongue.

Many of the symptoms caused by low B12 levels are not specific to B12 deficiency, which can cause the condition to go undetected.

If you’re experiencing any of the symptoms listed above, it’s important to visit a healthcare professional to undergo appropriate testing and get the right treatment.