Why Low Vitamin B12 Can Cause Fatigue and How to Support Healthy Levels
Why vitamin B12 deficiency can cause fatigue
Vitamin B12 is essential for making healthy red blood cells, maintaining nerves, and helping the body use energy from food. When B12 levels are too low, the body may not produce enough normal red blood cells to carry oxygen efficiently. Less oxygen delivery can make everyday activities feel harder and may lead to persistent fatigue, weakness, shortness of breath, or lightheadedness.
Low B12 can also affect the nervous system. Some people experience brain fog, mood changes, tingling in the hands or feet, balance problems, or numbness. Fatigue may appear gradually, so it is easy to mistake it for stress, poor sleep, or overwork.
Common signs that may occur with low B12
Fatigue is common, but it is not the only possible sign. Other symptoms can include weakness, pale skin, a fast heartbeat, dizziness, mouth soreness, appetite changes, unintentional weight loss, numbness or tingling, memory concerns, and mood changes. Symptoms vary, and some people have low B12 before obvious symptoms develop.
Who is more likely to have low vitamin B12
Risk is higher in people who eat little or no animal-based foods, including vegans and some vegetarians, because B12 is naturally found mainly in animal foods. Older adults may also be at higher risk because stomach acid often decreases with age, making B12 harder to absorb.
Other risk factors include pernicious anemia, digestive conditions such as Crohn disease or celiac disease, history of stomach or intestinal surgery, long-term use of certain acid-reducing medicines, and use of metformin. Pregnancy and breastfeeding can also increase the importance of adequate intake.
How to check vitamin B12 levels
If fatigue is persistent or unexplained, a healthcare professional may recommend blood tests. These may include serum vitamin B12, a complete blood count, methylmalonic acid, homocysteine, folate, and other tests depending on symptoms and medical history. Testing matters because fatigue has many possible causes, including iron deficiency, thyroid conditions, sleep problems, depression, infections, and chronic disease.
How to support healthy B12 levels
Food sources of vitamin B12 include fish, shellfish, meat, poultry, eggs, milk, yogurt, and cheese. Fortified foods, such as some breakfast cereals, nutritional yeast, and plant milks, can help people who limit animal products. Check labels because fortification levels vary.
Supplements may be useful for people with low intake or absorption challenges. Vitamin B12 supplements are available in forms such as cyanocobalamin and methylcobalamin. Some people with significant deficiency or absorption problems may need higher-dose oral B12 or injections prescribed by a healthcare professional.
When to seek medical care
Seek medical advice if fatigue is ongoing, severe, worsening, or paired with symptoms such as shortness of breath, chest pain, fainting, neurological changes, numbness, confusion, or difficulty walking. Early diagnosis and treatment are important because some nerve-related effects of B12 deficiency can become harder to reverse if deficiency continues.
Bottom line
Vitamin B12 deficiency can contribute to fatigue by affecting red blood cell production, oxygen delivery, and nerve health. A balanced diet, fortified foods, appropriate supplementation, and medical testing when symptoms persist can help support healthy B12 levels and overall energy.
