Vitamin B1 (Thiamine): Blood Test Guide

What is Vitamin B1

Vitamin B1, also known as thiamine, is a water-soluble vitamin essential for carbohydrate metabolism and nervous system function. It plays a role in energy production from food — without thiamine, the body cannot efficiently convert glucose into energy.

Thiamine is obtained from food: whole grain products, pork, legumes, seeds, and nuts. Vitamin B1 is not stored in large amounts in the body, so regular intake through diet is important.

In a blood test, thiamine is measured in whole blood (not just serum), because most thiamine is found in red blood cells.

Reference Ranges

Typical Vitamin B1 reference ranges in blood are 70–180 nmol/L. Laboratory ranges may vary depending on the method used, so always compare your result against the specific laboratory's reference limits.

A value below 70 nmol/L suggests a possible deficiency that may have clinical significance.

Why Vitamin B1 May Be Elevated

Elevated Vitamin B1 levels in the blood are rare and generally do not raise clinical concern. Because thiamine is water-soluble, excess is usually excreted through the kidneys.

High levels may be seen with large-dose B1 supplements or multivitamin preparations. Impaired kidney function can slow thiamine excretion and lead to higher levels.

Why Vitamin B1 May Be Low

The most common causes of low Vitamin B1 are inadequate nutrition and increased consumption. Alcohol use is one of the most significant risk factors — alcohol disrupts thiamine absorption in the intestine and increases its excretion.

Other causes include: unbalanced diet (especially one based on polished rice), chronic digestive disorders, long-term use of diuretics (which increase thiamine excretion in urine), diabetes mellitus (increased thiamine utilisation), and heart failure.

Severe B1 deficiency can cause beriberi (cardiac and neurological forms) or Wernicke's encephalopathy — an acute neurological disorder most commonly associated with alcoholism.

What to Do Next

If your Vitamin B1 level is low, discuss possible causes with your doctor. You may be advised to review your diet and include more thiamine-rich foods: whole grain bread, legumes, pork, and sunflower seeds.

If you drink alcohol regularly, this is important information for your doctor. Your doctor may recommend thiamine supplementation and monitoring for neurological symptoms.

If you take diuretics, additional Vitamin B1 assessment may be needed.

Monitoring Over Time

Vitamin B1 is not tested routinely — it is most often ordered for specific indications: neurological symptoms, history of alcohol use, heart failure, or unexplained fatigue.

If a deficiency is identified, a repeat test makes sense after 1–2 months once treatment has begun or diet has been adjusted. Related markers worth checking alongside: B12, folate, magnesium.

Questions for Your Doctor

1. Does my B1 level indicate a clinically significant deficiency? 2. Could my lifestyle or medications be contributing to B1 deficiency? 3. Should other B-group vitamins be tested? 4. How long should I take supplements if they are needed? 5. Could my symptoms be related to thiamine deficiency?