Vitamin B12 Deficiency: Causes, Symptoms, and What to Do

When your body doesn’t get enough vitamin B12, a crucial nutrient for nerve function and red blood cell production. Also known as cobalamin, it’s not made by the body—you must get it from food or supplements. Without enough, your nerves and blood cells start to break down, leading to symptoms that feel like burnout, but aren’t.

This isn’t just about being vegan or vegetarian. Even people who eat meat can develop vitamin B12 deficiency, often due to poor absorption rather than low intake. Conditions like pernicious anemia, an autoimmune disorder that stops stomach cells from making the protein needed to absorb B12, are a major cause. So are stomach surgeries, long-term acid reflux meds, and even aging. Your gut changes over time, and so does your ability to pull B12 from food.

Common signs include constant tiredness, tingling in hands or feet, trouble walking, memory lapses, and a swollen, red tongue. Many people think they’re just stressed or not sleeping well—but if these symptoms stick around, it’s not just fatigue. Low B12 affects your brain, your nerves, and your energy production at a cellular level. It’s not something you can ignore for long.

What you eat matters, but absorption matters more. Fortified cereals, eggs, dairy, and meat are good sources, but if your body can’t absorb them, supplements won’t help unless they’re in the right form. Sublingual tablets, injections, or nasal sprays bypass the gut and deliver B12 directly into your bloodstream. Doctors often start with shots for severe cases, then switch to high-dose pills once levels improve.

Testing for B12 isn’t always straightforward. A standard blood test might show "normal" levels, but your cells could still be starving. That’s why doctors sometimes check methylmalonic acid (MMA) or homocysteine—markers that rise when B12 is low, even before the main blood test shows it. If you’ve been told your levels are fine but still feel off, ask for these extra tests.

Left untreated, B12 deficiency can lead to permanent nerve damage. But caught early? It’s easily fixed. Most people feel better within weeks of starting treatment. The key is recognizing the signs before they turn into something serious.

Below, you’ll find real comparisons and guides on how B12 deficiency connects to other health issues—from thyroid problems and gut disorders to how certain medications interfere with absorption. These aren’t generic lists. Each post breaks down what actually works, what doesn’t, and why.