Vitamin B12 is a key nutrient involved in forming red blood cells, maintaining nerve function, and supporting DNA synthesis. Because the body cannot produce it, vitamin B12 must come from food or supplements. It is mainly found in animal-based products, so people who limit these foods may be at higher risk of deficiency. Absorption can also decline with age or certain digestive conditions, causing levels to drop slowly over time and making early symptoms easy to overlook.
One of the first signs of low vitamin B12 can be ongoing fatigue. This happens because the vitamin is essential for healthy red blood cells, which carry oxygen throughout the body. When production slows, oxygen delivery drops, leading to tiredness, weakness, or shortness of breath during routine activities. Some people notice lightheadedness, trouble concentrating, or mental fog, symptoms that are often mistaken for stress or lack of sleep.
Physical changes may appear as deficiency progresses. Pale or slightly yellow skin can develop due to changes in red blood cell health. Some people experience a smooth or sore tongue, along with mild mouth discomfort. More advanced deficiency can affect nerves, leading to tingling or numbness in the hands and feet, balance problems, or occasional vision disturbances.
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