Vitamin B12 is an essential nutrient that plays many critical roles in the body. When B12 levels are low, it can lead to a variety of symptoms and health issues. Recognizing the signs of B12 deficiency is important so that prompt treatment can be initiated.
What is Vitamin B12?
Vitamin B12, also known as cobalamin, is a water-soluble vitamin that is involved in the metabolism of every cell in the human body. It plays a vital role in:
- DNA synthesis
- Neurological function
- Formation of red blood cells
- Energy production
Vitamin B12 is unique in that it contains the mineral cobalt, which gives the vitamin its name. It’s the only vitamin that contains cobalt.
There are several different forms of B12 in supplements, including:
- Cyanocobalamin: The most common synthetic form used in supplements today.
- Methylcobalamin: An active form found in the body. Considered more bioavailable than cyancobalamin.
- Adenosylcobalamin: An active form found in the body. Also more bioavailable than cyanocobalamin.
Vitamin B12 is naturally found in animal foods, including meat, fish, eggs and dairy products. It can also be taken as a supplement.
Since vitamin B12 is a water-soluble vitamin, excess amounts are generally excreted in urine. Vitamin B12 deficiency is more likely to occur from inadequate intake rather than overconsumption.
Causes of Vitamin B12 Deficiency
There are two main causes of vitamin B12 deficiency:
- Inadequate Intake: This is most often caused by following a strict vegetarian or vegan diet. Plant foods do not contain vitamin B12 unless they are fortified. People following plant-based diets must take a vitamin B12 supplement or consume B12-fortified foods.
- Problems with Absorption: Certain conditions can affect the body’s ability to absorb vitamin B12 from foods. This includes:
- Atrophic gastritis
- Pernicious anemia
- Intestinal disorders such as Crohn’s disease or celiac disease
- Surgery removing parts of the stomach or small intestine
- Certain medications such as acid-reducing drugs and metformin
People over the age of 50 are also at greater risk of B12 deficiency because they are more likely to have decreased stomach acid levels required for B12 absorption from foods.
Symptoms of Vitamin B12 Deficiency
A vitamin B12 deficiency can often develop slowly over several years. Many of the symptoms are subtle at first but tend to worsen if the deficiency goes untreated.
Here are some of the most common symptoms of low B12 levels:
Fatigue and Low Energy
One of the earliest signs of B12 deficiency is constant tiredness and fatigue. This is thought to be related to impaired cellular metabolism and energy production.
A study in 152 women found that those with low B12 levels needed an average of 10 more hours of sleep and had less energy than those with normal B12 levels (1).
Chronic fatigue caused by low B12 can have a significant negative impact on your quality of life.
Muscle Weakness
Vitamin B12 plays a role in producing myelin, which protects and insulates nerve cells. When B12 levels are low, nerve transmission can be impaired.
This can result in muscle weakness, numbness and tingling in the hands and feet (2).
Research has linked low vitamin B12 levels to decreased muscle strength and performance in older adults (3).
Dizziness
Dizziness and loss of balance are common symptoms of B12 deficiency.
This is related to the neurological changes caused by low B12 levels affecting maintenance of balance and stability (4).
One study in 196 people with B12 deficiency found that 27% experienced dizziness (5).
Pins and Needles Sensations
Also referred to as paresthesia, pins and needles sensations can occur when nerve endings are not communicating properly with the brain. This numb, prickly feeling commonly affects the hands and feet but can also occur in other parts of the body.
A study including 689 young women found that numbness and tingling sensations in the hands and feet were reported more frequently among those with low B12 levels (6).
Pale Skin
Vitamin B12 plays an important role in producing red blood cells. When vitamin B12 levels are low, decreased red blood cell production can cause anemia, indicated by unusual paleness of the skin.
Research shows that adults with B12 levels below 185 pg/mL are at risk of anemia (7).
Mood Changes
In addition to physical symptoms, low B12 can lead to mental health changes including depression, anxiety and irritability.
One study found that healthy adults who received vitamin B12 injections reported feeling happier and more energetic. However, mood scores did not change for those who received a placebo injection, indicating that changes were due to the vitamin B12 (8).
Memory Loss
Vitamin B12 deficiency has been linked to memory issues, especially in older adults.
A study in 50 adults with depression found that 70% of those with low B12 levels had memory impairments compared to only 44% in those with normal B12 levels (9).
Research also indicates that vitamin B12 deficiency could contribute to a decline in brain volume and function in elderly people (10).
Vision Problems
Low B12 levels may lead to vision disturbances, including blurry vision, double vision, decreased peripheral vision or light sensitivity.
These changes are the result of damage to the optic nerve and can be severe if the deficiency goes untreated (11).
Glossitis
Glossitis refers to inflammation of the tongue. When your tongue changes color and becomes red and sore, often looking smooth and shiny, it’s known as “hunter’s tongue.”
Vitamin B12 deficiency can damage the mucous membranes and nerve cells of the tongue. Glossitis affects 5–20% of people with B12 deficiency (12).
Poor Reflexes
Healthy reflexes rely on good communication between your nerves and muscles. Since B12 is essential for nerve conduction, low levels can lead to delayed reflexes.
A physical exam can reveal slowed reaction times when your knees, ankles or arms are lightly tapped with a reflex hammer (13).
Long-Term Consequences of Vitamin B12 Deficiency
Left untreated, the neurological damage caused by vitamin B12 deficiency can become permanent. Long-standing deficiency can also increase the risk of:
- Neurological disorders like dementia, Alzheimer’s disease and Parkinson’s disease (14).
- Neuropsychiatric disorders, including paranoid delusions, hallucinations and major depression (15).
- Birth defects when vitamin B12 deficiency occurs during pregnancy, including neural tube defects (16).
That’s why it’s critical that a vitamin B12 deficiency is corrected as soon as possible, especially in women looking to become pregnant.
Who’s at Risk of B12 Deficiency?
Some people are at a higher risk of developing a vitamin B12 deficiency than others, including:
- Older adults: Decreased stomach acid production makes it harder to absorb vitamin B12 from foods (17).
- Vegetarians and vegans: Plant foods do not contain B12 unless fortified, putting strict vegetarians and vegans at particular risk (18).
- Those with GI disorders: Conditions like celiac disease and Crohn’s disease can affect the absorption of vitamin B12 from foods (19).
- Pregnant and breastfeeding women: Require higher amounts of B12 and are at increased risk of deficiency (20).
It’s important for these populations to be screened more frequently. Even mild deficiencies should be addressed promptly since B12 deficiency tends to worsen over time.
How Much Vitamin B12 Do You Need?
The recommended dietary allowance (RDA) for vitamin B12 is listed below:
| Age Group | Daily RDA |
|---|---|
| 0–6 months* | 0.4 mcg |
| 7–12 months* | 0.5 mcg |
| 1–3 years | 0.9 mcg |
| 4–8 years | 1.2 mcg |
| 9–13 years | 1.8 mcg |
| 14+ years | 2.4 mcg |
| Pregnancy | 2.6 mcg |
| Breastfeeding | 2.8 mcg |
*Adequate Intake (AI)
The amount of vitamin B12 you need depends on your age. Infants up to 6 months should have at least 0.4 mcg daily. Children require 0.9-1.8 mcg, while adults need 2.4 mcg.
Pregnant and breastfeeding women have slightly higher requirements at 2.6-2.8 mcg per day.
Food Sources of Vitamin B12
The best food sources of vitamin B12 include:
- Beef liver: 71 mcg per 3 oz (85 g)
- Sardines: 5.4 mcg per can
- Salmon: 4.5 mcg per 3 oz (85 g)
- Tuna: 2.5 mcg per 3 oz (85 g)
- Cod: 1.5 mcg per 3 oz (85 g)
- Swiss cheese: 1.5 mcg per 1 oz (28 g)
- Eggs: 0.6 mcg per large egg
- Milk: 0.5 mcg per cup (244 g)
All animal products contain at least traces of vitamin B12. However, levels are generally highest in organ meats, shellfish, beef, fish and dairy products.
Nutritional yeast is also often touted as a vegan source of vitamin B12. However, it contains vitamin B12 analogues that are not as bioavailable or beneficial to humans. Relying on nutritional yeast could worsen a deficiency over time.
While some plant milks and breakfast cereals are fortified with vitamin B12, supplements are recommended if you follow a strict vegan diet.
Treatment for Vitamin B12 Deficiency
Treating a vitamin B12 deficiency can prevent severe neurological complications. Here are some key treatment steps:
1. Increase Dietary B12 Intake
Eating more vitamin B12-rich animal foods can help raise B12 levels. However, absorption may continue to be impaired in those with gut disorders.
Vegans and vegetarians should take a daily B12 supplement to meet needs. Aim for at least 2.4 mcg per day for adults and higher doses in those who are deficient.
2. Vitamin B12 Injections
Vitamin B12 injections are often required to correct a deficiency, especially if nervous system damage is present. Typical protocols suggest an initial series of injections that may be given daily to weekly until levels improve.
Maintenance injections may be administered every 1–3 months, especially in those with impaired absorption. The frequency depends on the severity of the deficiency.
3. Address Underlying Causes
If a gut disorder is contributing to a B12 deficiency, work with a doctor to treat the condition whenever possible. This may include gluten elimination for celiac disease or anti-inflammatory medications for inflammatory bowel diseases.
Reducing or avoiding medications that interfere with B12 absorption, like metformin and PPIs, may also be considered under a doctor’s care.
Supplements and Dosing
Vitamin B12 is available in several forms as an oral supplement or injection.
Cyanocobalamin: This inactive form is generally used for fortifying foods and in less expensive supplements. However, it must be converted to active forms by the body.
Methylcobalamin: The activated form of B12 used directly in metabolic processes. Considered more effective, especially for neurological symptoms.
Adenosylcobalamin: The other active form of B12. Also highly effective, particularly for cellular energy production.
For deficiency treatment, methylcobalamin and adenosylcobalamin are preferred over cyanocobalamin injections.
Oral vitamin B12 supplements are effective at treating mild deficiencies without the need for injections. Look for a reputable brand providing at least 1,000 mcg of B12 in an active form like methylcobalamin or adenosylcobalamin.
Supplements should be taken in divided doses throughout the day for optimal absorption, such as 250–500 mcg taken 3–4x daily.
Signs of Excessive Vitamin B12
Vitamin B12 supplements and injections are considered very safe since any excess is usually excreted by the kidneys.
There are no serious adverse effects linked to high vitamin B12 intake from food or supplements. However, extremely high doses from supplements or injections could potentially cause acne.
Takeaway
Left untreated, vitamin B12 deficiency can cause severe neurological problems. Vitamin B12 testing and prompt treatment with supplements or injections should occur at the first sign of deficiency.
With early detection and proper treatment, you can reverse deficiency symptoms and avoid complications.