Why You Might Be Tired All the Time: Could It Be Low B12?

Fatigue is one of the most common things people bring to a provider — and one of the most common causes behind it is also one of the most overlooked: a real, testable B12 deficiency, rather than just "needing more sleep."

What B12 actually does in the body

Vitamin B12 is involved in red blood cell formation, nerve function, and DNA synthesis, and it plays a direct role in cellular energy production. When levels are genuinely low, the body's ability to transport oxygen and produce energy at the cellular level is affected — which shows up as fatigue that doesn't resolve with rest.

Who's actually at risk

B12 deficiency isn't universal, and it isn't random either. It's more common in people following vegetarian or vegan diets (B12 comes primarily from animal products), people with certain absorption issues that become more common with age, and people on certain long-term medications, including some acid reducers and metformin. It's worth checking, not assuming.

Symptoms worth paying attention to

Persistent fatigue, brain fog, low mood, and — in more pronounced cases — tingling or numbness in the hands or feet are the symptoms most associated with low B12. Because these overlap with many other conditions, symptoms alone aren't a diagnosis; they're a reason to test.

Why testing matters before supplementing

A blood test — B12 levels, sometimes alongside methylmalonic acid or homocysteine for a fuller picture — is what actually confirms a deficiency, rather than guessing based on symptoms or assuming everyone is low. Testing first also avoids masking an unrelated cause of fatigue that deserves its own attention.

Why injectable B12 is often used for a confirmed deficiency

For people with an absorption-related cause, oral B12 can be inconsistent, since the same absorption issue affects how much of an oral dose is actually used. An injectable form bypasses that step, which is why it's commonly used once a real deficiency is confirmed rather than as a general assumption.

How Feelrx approaches energy and fatigue

Fatigue has a lot of possible causes, and B12 is one of the more treatable ones when it's the actual issue — which is why this starts with your history and, where appropriate, lab work, rather than a blanket recommendation.

This article is for general educational purposes and is not medical advice, and does not guarantee any specific result. All prescription treatments discussed require an evaluation by a licensed healthcare provider, who will determine whether a treatment is appropriate based on individual health history.