And What Happens When You Don’t Get Enough
Introduction
Vitamin B12 might not get as much attention as other nutrients like vitamin C or calcium, but it plays a vital role in keeping your body running smoothly. It’s essential for keeping your nerves healthy and for helping your body produce red blood cells — the cells that carry oxygen throughout your body. Without enough B12, you can feel tired, weak, foggy, and even experience nerve problems. One of the most serious outcomes of B12 deficiency is something called pernicious anemia, where the body can’t make enough healthy red blood cells.
So how does someone end up low in B12? There are a few main reasons — and many of them have nothing to do with how much you’re eating, but rather how well your body can absorb the vitamin.
Diet and B12 Deficiency
The first and most obvious reason for low B12 is simply not getting enough of it from food. Vitamin B12 is found naturally in animal-based foods such as meat, fish, eggs, and dairy. That means if you’re following a vegan or strict vegetarian diet and not taking B12 supplements, you’re at higher risk of becoming deficient. Even diets high in processed foods can fall short of B12, especially if they lack real, whole foods.
Trouble Absorbing B12
Even if your diet contains plenty of B12, your body still has to be able to absorb it properly. And that’s where things can get tricky.
B12 is absorbed in a specific part of the small intestine called the terminal ileum. But before it even gets there, it needs help. In the stomach, a special protein called intrinsic factor binds to B12 and helps it travel through the digestive system for absorption. If this process is interrupted, B12 can’t be absorbed well — no matter how much you’re eating.
Damage to the small intestine, as in celiac disease or after certain surgeries, can interfere with absorption. A rare kind of tapeworm infection (Diphyllobothrium latum) can also disrupt B12 absorption by competing for the vitamin inside the digestive tract.
When the Body Can’t Make Intrinsic Factor
Sometimes the problem isn’t the intestines at all — it’s that your body isn’t making enough intrinsic factor. This can happen for a few reasons. The most common is a condition called pernicious anemia, where the immune system mistakenly attacks the stomach cells that produce intrinsic factor. Without it, B12 can’t be absorbed, and over time, deficiency develops.
Gastric surgeries, such as gastric bypass for weight loss, can also reduce the size of the stomach and limit the production of intrinsic factor. This makes it harder for the body to absorb B12 naturally from food, and often people who undergo these surgeries need lifelong B12 supplementation.
Why This Matters
The symptoms of B12 deficiency can start slowly and are easy to overlook — things like fatigue, memory issues, or numbness in the hands and feet. But over time, the effects can become serious and even permanent if not addressed. That’s why it’s important to catch and correct B12 deficiency early.
Fortunately, the solution is usually simple: dietary adjustments, oral supplements, or in more severe cases, B12 injections. If you follow a plant-based diet or have had any digestive issues or surgeries, it’s worth checking your B12 levels regularly.
B12 may be a small vitamin, but its impact on your health is anything but small. Making sure you’re getting enough — and absorbing it properly — is one of the simplest steps you can take to protect your energy, your brain, and your long-term health.