You've been feeling tired and a friend suggests a B12 supplement. It might sound like an easy fix, but tiredness can have many causes. A symptom alone cannot tell you whether you have a B12 deficiency.
B12 is worth discussing when your diet has changed, when you have a condition that affects absorption, or when you take certain medicines. The useful next step is to understand your own situation rather than guessing from a social post.
What B12 does
Vitamin B12 helps keep nerve and blood cells healthy and supports the body's production of DNA. Your body needs a reliable source, but the amount you eat is only part of the story: your body also has to absorb it.
If you have a concern about a possible deficiency, a health professional can ask about your symptoms, food intake, medicines and medical history, then decide whether testing is appropriate. Bring up changes in how you feel even if you're not sure they're related.
Foods that contain B12
Fish, meat, poultry, eggs, milk and other dairy foods contain B12. Some cereals, nutritional yeasts and other products have B12 added. Check the label for fortified foods, because not every product in the same category contains the same nutrients.
Plant foods don't naturally provide B12 unless they are fortified. If you eat a vegan diet or rarely eat animal foods, discuss a reliable source of B12 with a dietitian or other qualified professional. Our guide to vegetarian and vegan eating while taking a GLP-1 covers broader meal planning.
If you use nutritional yeast, compare the B12 amount and serving size on the package you buy. Different brands and varieties may have different amounts added.
For someone with a smaller appetite, an egg with toast, a small yogurt or a fortified food may fit more comfortably than a large meal. Those are examples, not a personalized treatment plan. A dietitian can help you check whether your overall routine meets your needs.
Absorption matters too
Some people have trouble absorbing B12 even when their food intake looks adequate. Certain stomach or intestinal conditions and some previous procedures can affect absorption. Age and medicines can matter as well.
For example, metformin can reduce B12 absorption. In a long-term study, low or borderline B12 levels were more common in a metformin group at the points researchers measured. That doesn't mean everyone taking metformin will become deficient, and it isn't a reason to stop it on your own.
If metformin or another medicine is part of your care, ask whether B12 should be checked for you and when. Bring a current medicine list, including over-the-counter products, to make the discussion easier.
What if you're taking a GLP-1?
A change in appetite can change your usual foods, but it doesn't automatically mean a GLP-1 has caused a B12 deficiency. Tell your care team if you're skipping foods you relied on, eating very little or having persistent symptoms that make meals difficult.
You can ask, “Are there nutrients we should pay attention to with the way I'm eating now?” A short description of a typical day is enough to start; you don't need a perfect food diary.
A note about supplements
B12 comes in several supplement forms, and treatment for a confirmed deficiency depends on its cause. If a professional recommends a product or prescription treatment, ask how it fits with your other medicines and follow that plan.
Supplements marketed for energy won't necessarily help someone who already gets enough B12. If fatigue is new, persistent or disruptive, ask about an evaluation rather than assuming one vitamin explains it.
The goal is straightforward: find a dependable source, understand whether absorption is a concern and get help with symptoms that aren't resolving.