Vitamin B12 is an essential nutrient that supports nerve health, brain function, and the production of healthy blood cells. It also helps the body create DNA and convert food into energy. Because deficiency often develops gradually, many people don’t realize their levels are low until symptoms begin to appear, and early warning signs can easily be overlooked.

One of the most common symptoms is persistent fatigue. Vitamin B12 is needed to produce red blood cells that carry oxygen throughout the body, so when levels drop, oxygen delivery becomes less efficient. As a result, people may feel constantly tired, weak, or drained even after adequate rest.

Low vitamin B12 can also affect the nervous system. Tingling or numbness in the hands and feet—often described as a “pins and needles” sensation—can occur when the protective covering around nerves becomes damaged. Some people may also notice memory problems, difficulty concentrating, or mental “brain fog,” since B12 plays an important role in maintaining normal brain function.

Changes in appearance or physical comfort can also signal a deficiency. The skin may appear unusually pale or slightly yellow due to abnormal red blood cell breakdown and increased bilirubin levels. Some individuals develop a swollen, smooth, or glossy tongue, sometimes accompanied by burning sensations or mouth discomfort.

Because reduced red blood cell production limits oxygen supply, people with low B12 may experience dizziness, lightheadedness, or shortness of breath during normal activities such as walking or climbing stairs. Mood changes can also occur, including irritability, mood swings, or symptoms of depression, possibly linked to the vitamin’s role in producing brain chemicals that regulate mood.

In more serious or prolonged cases, vitamin B12 deficiency may affect vision or the nervous system. Blurred vision can occur if the optic nerve becomes affected, and untreated deficiency may lead to balance and coordination problems. If several of these symptoms appear, medical advice is important. A simple blood test can check vitamin B12 levels, and treatment may include dietary adjustments, supplements, or injections. Since B12 is mainly found in animal products like meat, eggs, and dairy, older adults, vegetarians, vegans, and people with certain digestive conditions may be at higher risk of deficiency.