Vitamin B12 plays a critical role in nerve function, red blood cell production, and cognitive health, yet many people don’t realize they’re deficient until symptoms become disruptive. According to registered dietitian and molecular biologist Andreea Nitescu, vitamin B12 deficiency tends to affect multiple systems in the body at once.
“Vitamin B12 deficiency often shows up in both the nervous system and the blood, so symptoms are most typically physical, neurological, or cognitive,” Nitescu explains.
Here are six common signs your body may be low in B12, including one that directly impacts memory and focus.
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1. Tingling or ‘Pins-and-Needles’ Sensations
One of the earliest and most recognizable signs of low B12 is tingling in the hands or feet. This sensation, known as paresthesia, occurs when nerves aren’t properly protected.
“B12 is essential for maintaining the myelin sheath around nerves. Low levels can cause numbness or tingling in the hands and feet,” Nitescu explains. If the deficiency continues untreated, nerve damage can become more severe and harder to reverse.
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2. Extreme Fatigue and Low Energy
Feeling constantly exhausted—even after adequate rest—can also point to a B12 deficiency. This nutrient is vital for producing red blood cells and supporting energy metabolism.
“B12 is required for red blood cells to form and for cellular energy production,” Nitescu says. When levels are too low, oxygen delivery throughout the body is compromised, often leading to persistent fatigue and poor exercise tolerance.
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3. Weakness or Muscle Fatigue
Low B12 doesn’t just sap energy—it can also weaken muscles. People may notice they tire more easily during physical activity or feel generally weaker.
“Reduced oxygen delivery to tissues due to B12-related anemia can cause generalized weakness,” Nitescu notes. This symptom is especially common when deficiency affects red blood cell production over time.
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4. Pale or Yellowish Skin
Changes in skin tone can be another subtle warning sign.
“Impaired red blood cell production can lead to paleness, while increased breakdown of red blood cells may cause a subtle yellow tint,” Nitescu explains. These changes are often overlooked but can signal an underlying nutrient imbalance.
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5. Sore or Swollen Tongue (Glossitis)
A tongue that feels sore, swollen, or unusually smooth can be an early sign of B12 deficiency, though it’s often overlooked.
“A smooth, inflamed, or burning tongue is a classic but often overlooked sign of B12-related anemia,” Nitescu says. This symptom occurs because cells in the mouth divide rapidly and are particularly sensitive to nutrient deficiencies.
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6. Cognitive and Mood Changes
B12 deficiency can also affect the brain, sometimes before physical symptoms become obvious.
“This includes memory issues, difficulty concentrating, confusion, irritability, and depressive symptoms, sometimes even before anemia appears,” Nitescu explains. Many people mistake these cognitive changes for stress or aging, delaying proper diagnosis.
How to Support Healthy B12 Levels
Preventing or treating a B12 deficiency should start with diet. “It is naturally found in animal foods such as meat, fish, shellfish, eggs, and dairy,” Nitescu notes, which is why people who eat little to no animal products are at higher risk and often need supplementation.
If supplementing, the type of B12 matters. “Methylcobalamin and adenosylcobalamin are the active forms the body actually uses,” she explains, while cyanocobalamin must be converted and may be less effective for many people. Research also suggests cyanocobalamin may negatively influence the gut microbiome over time. Absorption issues can further complicate deficiency.
Alcohol use, low stomach acid, medications like proton pump inhibitors or metformin, and digestive conditions can all interfere with B12 uptake. In those cases, “sublingual B12 or injectable forms may be more effective options for restoring and maintaining healthy levels,” Nitescu advises.
If symptoms like tingling, fatigue, or memory issues sound familiar, testing your B12 levels could be a crucial step toward protecting your energy, nerves, and brain health.