Does Lack of B12 Make You Sick? Understanding the Symptoms and Effects

November 16, 2025 •

4 min read

According to the National Institutes of Health, vitamin B12 deficiency affects a significant portion of the population, especially older adults. A lack of B12 can indeed make you sick, causing a wide range of physical, neurological, and psychological symptoms that can worsen over time if left untreated.

Quick Summary

A deficiency in vitamin B12 can cause significant health problems, leading to a spectrum of physical, neurological, and psychological symptoms. Recognizing the signs is key, as early treatment can reverse most issues, while delayed intervention might lead to permanent nerve damage. Causes range from diet to medical conditions affecting absorption.

Key Points

Sickness is a possibility: Lack of B12 can indeed cause illness, ranging from mild fatigue to severe neurological issues.
Symptoms are wide-ranging: A deficiency impacts multiple body systems, leading to physical, neurological, and mental health symptoms.
Neurological damage can be permanent: If untreated, a severe B12 deficiency can cause irreversible nerve damage, affecting balance, coordination, and memory.
Causes vary: While diet is a factor, malabsorption issues like pernicious anemia and gastric surgery are common causes.
Early diagnosis is key: Timely detection through blood tests and proper treatment, often with injections, can prevent long-term complications.
Vegetarians and older adults are at risk: People on a plant-based diet and those with decreased stomach acid should be particularly mindful of their B12 intake.

The Core Role of Vitamin B12 in Your Body

Vitamin B12, or cobalamin, is a water-soluble vitamin essential for numerous bodily functions. It plays a critical role in producing red blood cells and DNA, as well as maintaining the health of your nerve cells. Since the human body does not produce B12, it must be obtained through animal-based foods, supplements, or fortified products. A deficiency occurs when there isn't enough intake or, more commonly, when the body cannot properly absorb it. Your body has a large store of B12 in the liver, which means symptoms can develop very slowly over many years.

Can a lack of B12 really make you sick?

Yes, a lack of B12 can make you sick, and the severity can range from mild and subtle symptoms to serious, life-altering conditions. The insidious nature of its slow onset means many people mistake the initial signs for normal aging or stress. The illness manifests across multiple body systems because B12 is vital for so many cellular processes. Problems can occur in your blood, nervous system, and even your mental health.

Common physical symptoms

One of the most well-known consequences of B12 deficiency is megaloblastic anemia, a condition where the body produces abnormally large red blood cells that cannot function properly. This impairs oxygen delivery throughout the body, leading to a cascade of symptoms. Physical symptoms include:

Chronic fatigue and weakness: A persistent feeling of tiredness or a lack of energy is one of the earliest and most common indicators.
Pale or yellowish skin (jaundice): A lack of healthy red blood cells can lead to a paler complexion or a slight yellowing of the skin and eyes.
Sore and red tongue (glossitis): This is a classic sign, often accompanied by mouth ulcers.
Gastrointestinal issues: Digestive problems like diarrhea, constipation, nausea, and loss of appetite are frequently reported.
Heart palpitations: The heart may beat faster to compensate for the lack of oxygen-carrying red blood cells, causing palpitations.

Neurological and psychological symptoms

B12's crucial role in nerve health means a deficiency can lead to significant neurological and psychological problems. If left untreated, some of this nerve damage can become permanent. Neurological signs include:

Pins and needles or numbness: Paresthesia, or a tingling sensation, often in the hands and feet, is a hallmark symptom.
Difficulty with balance and coordination (ataxia): Damage to the spinal cord can lead to an unsteady gait and trouble with physical coordination.
Cognitive difficulties: Memory loss, confusion, and a decline in mental ability, sometimes mimicking dementia, are possible, especially in older adults.
Psychiatric symptoms: Mood changes such as depression, anxiety, irritability, and even paranoia or delusions can occur in severe cases.
Vision problems: In some instances, optic nerve damage can cause disturbed or blurred vision.

Risk factors for B12 deficiency

Certain factors increase your risk of developing a B12 deficiency:

Dietary choices: Vegans and strict vegetarians are at risk because B12 is found almost exclusively in animal products.
Age: Older adults often have reduced stomach acid, which is necessary to release B12 from food.
Gastrointestinal surgery: Procedures like gastric bypass can reduce the body's ability to absorb B12.
Pernicious anemia: This autoimmune condition prevents the stomach from producing intrinsic factor, a protein required for B12 absorption.
Medications: Some drugs, such as metformin (for diabetes) and long-term heartburn medication (PPIs), can interfere with B12 absorption.
Digestive disorders: Conditions like Crohn's disease and celiac disease can impact nutrient absorption in the gut.

Comparison of B12 Deficiency Effects


Symptom Category	Mild Deficiency Effects	Severe/Chronic Deficiency Effects
Physical	Fatigue, weakness, pale skin, sore tongue	Severe anemia, rapid heart rate, heart failure
Neurological	Tingling in hands/feet, mild memory issues	Permanent nerve damage, ataxia (balance issues), severe memory loss
Psychological	Irritability, mood swings, mild depression	Confusion, dementia, paranoia, delusions, psychosis
Gastrointestinal	Nausea, loss of appetite, diarrhea	Prolonged gut problems, risk of stomach cancer in pernicious anemia

Diagnosis and treatment

Diagnosing a B12 deficiency typically involves a blood test to measure the vitamin levels, and sometimes additional tests like methylmalonic acid (MMA) and homocysteine levels. The treatment approach depends on the underlying cause. For dietary deficiencies, supplements or fortified foods may be enough. However, for pernicious anemia and other malabsorption issues, vitamin B12 injections are often necessary. Early diagnosis is key to preventing long-term, irreversible nerve damage. If you suspect you have a B12 deficiency, it is important to consult a healthcare professional. For more information on vitamin B12, including dietary sources, consult the NIH Office of Dietary Supplements.

Conclusion

In conclusion, a lack of B12 can make you very sick, with consequences spanning from general fatigue to severe, and in some cases, permanent neurological damage. The wide array of potential symptoms, including physical weakness, nerve problems, and psychological issues, underscores the importance of this essential nutrient. While the body can store B12 for a long time, persistent deficiency due to diet or absorption problems must be addressed promptly to prevent long-term health complications. A professional diagnosis and appropriate treatment are essential for recovery and maintaining overall health.

Frequently Asked Questions

The earliest signs of B12 deficiency often include persistent fatigue, weakness, and lightheadedness. These may be accompanied by a sore tongue, loss of appetite, and mood changes like irritability or depression.

Yes, a long-term or severe B12 deficiency can cause significant nerve damage, known as peripheral neuropathy. Symptoms include numbness, tingling, and difficulties with balance and coordination. In some cases, this damage can be permanent.

No, it is possible to have a B12 deficiency and experience neurological symptoms even without developing megaloblastic anemia, where red blood cells are abnormally large. This is why a B12 deficiency can be hard to detect without proper testing.

Individuals at a higher risk include older adults, people following vegan or strict vegetarian diets, those with autoimmune conditions like pernicious anemia, and individuals who have had gastrointestinal surgery or certain digestive diseases.

A diet lacking in animal products is a known cause of B12 deficiency, as the vitamin is primarily found in meat, eggs, and dairy. However, it is more common for the deficiency to be caused by an inability to absorb the vitamin, even with adequate dietary intake.

Treatment depends on the cause. For dietary inadequacy, oral supplements or fortified foods may be sufficient. For malabsorption issues like pernicious anemia, vitamin B12 injections are often necessary to bypass the digestive tract and ensure proper absorption.

Yes, a lack of B12 can have a significant impact on mental health. Symptoms can range from irritability and mild depression to more severe psychiatric issues like confusion, memory loss, paranoia, and delusions.

Because the body stores a large amount of B12, a deficiency can take several years to develop. Symptoms can emerge gradually and intensify over a long period, making them easy to overlook in the early stages.