Chapter 2: Persistent Fatigue May Be More Than Just Being Tired

Almost everyone feels exhausted sometimes.

A demanding week at work, several nights of poor sleep, intense exercise, stress, or caring for family members can leave a person feeling completely drained.

But B12 deficiency can produce a type of fatigue that does not necessarily improve simply by getting more rest.

When B12 deficiency leads to anemia, the blood may have a reduced ability to transport oxygen efficiently. This can contribute to weakness, reduced exercise tolerance, dizziness, and shortness of breath.

Someone who previously walked several kilometers without difficulty may suddenly find themselves becoming exhausted after a much shorter distance.

Climbing stairs may feel unusually difficult.

Even ordinary household activities can begin to require more effort.

These changes can develop gradually, making them surprisingly easy to overlook.

A person may think:

“I must just be getting older.”

“I've been working too much.”

“I haven't been sleeping well.”

“My stress levels are high.”

Those explanations may be correct.

But if fatigue persists for weeks or is accompanied by other unusual symptoms, it deserves evaluation.

B12 deficiency can also occur alongside other nutritional deficiencies, which means a doctor may consider more than one possible explanation.

Diet is one factor.

Vitamin B12 naturally occurs primarily in animal-derived foods such as meat, fish, eggs, and dairy products. People following strict vegan diets without fortified foods or supplementation can therefore be at increased risk of deficiency.

But diet is not the only issue.

Some people consume enough B12 but cannot absorb it properly.

Conditions affecting the stomach or small intestine can interfere with absorption. Certain medications can also reduce B12 absorption over time.

This is why simply eating more meat is not necessarily the answer for everyone.

If absorption is the problem, the underlying condition may need to be addressed.

Blood testing can help distinguish B12 deficiency from other causes of fatigue.

Depending on the situation, clinicians may evaluate B12 levels along with other blood markers, including measures related to red blood cells and, when appropriate, methylmalonic acid or homocysteine.

The important takeaway is simple:

Persistent fatigue is a symptom—not a diagnosis.

If your energy has changed significantly without an obvious explanation, don't automatically blame age or a busy lifestyle.