Vitamin B12 Deficiency: Symptoms, Causes & How to Fix It Naturally
Last updated August 2026 · 12 min read
Quick Answer
Vitamin B12 deficiency often causes fatigue, brain fog, numbness or tingling in the hands and feet, and pale skin, developing slowly because the liver stores several years' worth of B12. It's most common in vegetarians and vegans, older adults with reduced stomach acid, people with digestive absorption issues, and those on certain long-term medications. Treatment typically involves oral supplements or B12 injections, guided by a blood test and a doctor's recommendation.
Of all the nutrient deficiencies that quietly affect how people feel day to day, vitamin B12 might be the one with the widest range of symptoms — and the slowest, sneakiest onset. Because your liver can store several years' worth of B12, a deficiency doesn't show up overnight. It builds gradually, over months or even years, which means by the time symptoms become noticeable, the deficiency may already be fairly advanced.
B12 plays a central role in two systems that affect how you feel every single day: your nervous system and your red blood cell production. When levels drop, the effects can range from mild fatigue and brain fog to, in more serious and prolonged cases, nerve damage that doesn't fully reverse. That range is exactly why understanding this deficiency — and who's actually at risk — matters.
This guide covers what B12 does, the symptoms and causes of deficiency, who should be paying closer attention, and how it's typically corrected.
What Vitamin B12 Actually Does in Your Body
- Red blood cell formation — B12 is essential for producing healthy, properly sized red blood cells; deficiency can lead to a specific type of anemia called megaloblastic anemia
- Nervous system function — it's required to maintain the protective coating (myelin) around nerves, which is why prolonged deficiency can cause nerve-related symptoms
- DNA synthesis — B12 is a cofactor in DNA production, relevant to cell division throughout the body
- Energy metabolism — it plays a role in converting food into usable cellular energy
- Brain function — adequate B12 is linked to cognitive function, and severe deficiency has been associated with memory problems and confusion, particularly in older adults
Unlike many vitamins, B12 is found almost exclusively in animal-based foods, which is the single biggest reason deficiency risk varies so much between different diets and populations.
Common Symptoms of Vitamin B12 Deficiency
Fatigue and Weakness
Because B12 deficiency can lead to fewer healthy red blood cells to carry oxygen, fatigue and general weakness are among the most common early symptoms.
Numbness or Tingling
A pins-and-needles sensation, often starting in the hands or feet, can develop as B12 deficiency begins to affect nerve function. This symptom deserves prompt medical attention rather than waiting it out.
Brain Fog and Memory Issues
Difficulty concentrating, forgetfulness, and a general mental fogginess are commonly reported, and can be mistaken for normal aging or stress, especially in older adults.
Pale or Yellowish Skin
Because B12 deficiency affects red blood cell production, some people develop a pale or slightly yellow-tinged skin tone, related to the breakdown of abnormal red blood cells.
Shortness of Breath and Dizziness
These can occur as a result of reduced oxygen-carrying capacity in the blood when red blood cell production is impaired.
Mood Changes
Some people notice irritability or low mood alongside other symptoms, potentially related to B12's role in neurotransmitter function.
A Smooth, Sore Tongue
A specific but lesser-known sign, sometimes called glossitis, involves the tongue becoming unusually smooth, red, or sore.
Balance Problems
In more advanced cases, nerve involvement can affect coordination and balance, increasing fall risk, particularly in older adults.
What Causes Vitamin B12 Deficiency?
Low Dietary Intake
Since B12 occurs almost exclusively in animal products — meat, fish, eggs, and dairy — vegetarians, and especially vegans, are at meaningfully higher risk unless they use fortified foods or supplements.
Reduced Stomach Acid
Absorbing B12 from food requires adequate stomach acid to release it from protein. Stomach acid production naturally declines with age, and long-term use of acid-reducing medications (like proton pump inhibitors) can further impair absorption.
Pernicious Anemia
This autoimmune condition affects the body's ability to produce intrinsic factor, a protein required to absorb B12 in the small intestine. It's one of the more well-known medical causes of B12 deficiency and typically requires B12 injections rather than oral supplements.
Digestive Conditions and Surgeries
Conditions like Crohn's disease and celiac disease, as well as a history of gastric bypass or other bariatric surgery, can significantly impair B12 absorption regardless of dietary intake.
Certain Medications
Long-term use of metformin, a common medication for type 2 diabetes, and acid-reducing medications are both associated with reduced B12 absorption over time.
Age
Older adults are at meaningfully higher risk due to a combination of reduced stomach acid, higher rates of digestive conditions, and dietary changes that sometimes come with aging.
Who's Most at Risk?
- Vegetarians and, especially, vegans
- Adults over 60
- People with pernicious anemia or other autoimmune digestive conditions
- People who've had gastric bypass or other bariatric surgery
- People on long-term metformin or acid-reducing medications
- People with Crohn's disease, celiac disease, or other malabsorption conditions
- Pregnant and breastfeeding women, who have increased B12 needs
How Vitamin B12 Deficiency Is Diagnosed
A blood test measuring serum B12 levels is the standard first step. Because borderline results can be ambiguous, doctors sometimes also check related markers, such as methylmalonic acid (MMA) or homocysteine levels, which tend to rise when B12 is functionally low even if the standard test result looks borderline-normal. If pernicious anemia is suspected, additional antibody testing may be used to confirm the underlying cause.
Food Sources of Vitamin B12
| Food | Serving Size | Approx. B12 | % of Daily Value* |
|---|---|---|---|
| Clams (cooked) | 3 oz | ~84 mcg | 3,500% |
| Beef liver (cooked) | 3 oz | ~70 mcg | 2,900% |
| Salmon (cooked) | 3 oz | ~2.6 mcg | 108% |
| Tuna (cooked) | 3 oz | ~2.5 mcg | 104% |
| Fortified nutritional yeast | 2 tbsp | ~7.8 mcg | 325% |
| Egg | 1 large | ~0.6 mcg | 25% |
| Fortified plant milk | 1 cup | ~1–3 mcg (varies by brand) | 40–125% |
| Greek yogurt | 1 cup | ~1.3 mcg | 54% |
*Based on a general adult daily value of 2.4 mcg. Values vary by product and brand for fortified foods.
Recommended Daily B12 Intake by Age
| Age Group | Recommended Daily Intake |
|---|---|
| Adults (19+) | 2.4 mcg |
| Pregnancy | 2.6 mcg |
| Breastfeeding | 2.8 mcg |
How B12 Deficiency Is Typically Treated
Oral Supplements
For mild to moderate deficiency, particularly related to low dietary intake, oral B12 supplements — often in fairly high doses — can be effective, since even people with reduced absorption can absorb a small percentage of a large oral dose through a passive mechanism.
B12 Injections
For more severe deficiency, absorption disorders like pernicious anemia, or cases where oral supplementation isn't effectively raising levels, doctors often prescribe B12 injections, which bypass the digestive absorption process entirely.
Dietary Adjustments
For those able to include animal products, increasing intake of foods like eggs, dairy, fish, and meat can help. For vegans and strict vegetarians, fortified foods and a reliable supplement are generally necessary rather than optional.
Addressing the Underlying Cause
If deficiency stems from a medication or an underlying digestive condition, addressing that root cause alongside supplementation, in consultation with your doctor, gives the best long-term outcome.
B12 is one of several key nutrients that quietly affect energy and mood. Check out our related guides on vitamin D deficiency and magnesium deficiency to see the fuller picture.
Can You Take Too Much B12?
Vitamin B12 is water-soluble, meaning excess amounts are generally excreted through urine rather than stored to harmful levels, which is why it's considered to have a low risk of toxicity compared to fat-soluble vitamins. That said, very high doses should still be taken under medical guidance, particularly if you're addressing a diagnosed deficiency rather than just general maintenance.
When to See a Doctor
- Persistent fatigue that doesn't improve with rest
- Numbness, tingling, or balance issues, especially if new or worsening
- Memory problems or confusion that seem out of the ordinary
- You follow a vegan or strict vegetarian diet without a reliable B12 source
- You have a digestive condition or take medications known to affect B12 absorption
Because some of B12 deficiency's effects, particularly nerve-related symptoms, can become harder to reverse the longer they go untreated, it's worth getting checked sooner rather than waiting to see if symptoms resolve on their own.
Frequently Asked Questions
What are the early signs of vitamin B12 deficiency?
Early signs often include fatigue, weakness, mild memory issues, and pale skin. Because B12 stores in the liver can last for years, symptoms tend to develop slowly and are easy to overlook at first.
Who is most at risk of vitamin B12 deficiency?
Vegetarians and vegans, older adults, people with digestive conditions affecting absorption, and people taking certain long-term medications such as metformin or acid reducers are at higher risk.
Can B12 deficiency cause permanent nerve damage?
If left untreated for a prolonged period, severe B12 deficiency can lead to nerve damage that may not fully reverse even after treatment, which is why early diagnosis and correction matter.
How is vitamin B12 deficiency treated?
Treatment typically involves oral supplements or, for more severe cases or absorption issues, B12 injections prescribed by a doctor. The right approach depends on the underlying cause and severity.
Can vegans get enough B12 from food?
It's very difficult, since B12 is found almost exclusively in animal products. Most health organizations recommend that vegans use a B12 supplement or B12-fortified foods rather than relying on diet alone.
How long does it take to correct a B12 deficiency?
Mild deficiencies may improve within a few weeks of supplementation, while more severe or long-standing deficiencies, especially those involving nerve symptoms, can take several months to improve and may not fully resolve.
The Bottom Line
Vitamin B12 deficiency is one of the more consequential nutrient gaps precisely because it builds so gradually and touches both your nervous system and your blood. The slow onset means that by the time fatigue, numbness, or brain fog become impossible to ignore, it's worth taking seriously rather than assuming it's just stress or aging.
If you fall into one of the higher-risk categories — plant-based eaters, older adults, or anyone on long-term medications known to affect absorption — a simple blood test can settle the question quickly, and correction, whether through diet, oral supplements, or injections, tends to be straightforward once the cause is identified.