Vitamin B1 (thiamine)
Water-soluble B vitamin that helps cells turn carbohydrates into energy
Also known as
Definition
Vitamin B1 (thiamine) is one of the water-soluble B vitamins. It helps the body's cells turn carbohydrates into energy, which the brain and nervous system in particular need, and is involved in the metabolism of pyruvate. It also plays a role in muscle contraction and the conduction of nerve signals. A vitamin B test can measure the level in blood or urine.
| Parameter | Value |
|---|---|
| Unit | nmol/l or µg/l, depending on lab and method |
| Reference Range | No single range: labs use their own reference ranges depending on the sample (blood or urine) and method, and for some B vitamins it is not fully settled what a normal level is. The range on your own report is what counts; discuss deviations with your doctor. |
Agree on your personal target range with your doctor.
↓ What a low value means
A low value may be related to low intake or impaired use. Deficiency is most often seen with excessive alcohol use, usually due to alcohol use disorder; alcohol makes it harder to absorb thiamine from food. Other risks include celiac disease, Crohn's disease and other absorption disorders, surgery on the digestive tract, dialysis and high-dose diuretics. A deficiency can cause weakness, fatigue, confusion and nerve damage; severe forms can cause beriberi or Wernicke-Korsakoff syndrome. Your doctor handles the assessment.
↑ What a high value means
According to MedlinePlus, no poisoning from excessive thiamine intake is known. For B vitamins in general: high levels can cause problems or may be related to an underlying condition such as liver disease. Discuss a raised value with your doctor.
When to test
A test is considered with symptoms that fit a deficiency or with risk factors such as alcohol use disorder, absorption disorders in the gut, surgery on the digestive tract or medicines that affect how B vitamins are used. Fasting for a few hours may be needed before a blood draw. Inflammation and some medicines can affect the result.
Frequently asked questions
How is vitamin B1 measured? +
In blood or urine. For a urine test, either a single sample or all urine over 24 hours is collected. Before a blood draw, you may need to fast for a few hours; your practice or lab will give you the instructions.
Who has a higher risk of a low B1 level? +
Mainly people with alcohol use disorder, with absorption disorders such as celiac disease or Crohn's disease, after surgery on the digestive tract including gastric bypass, on dialysis or on high-dose diuretics.
What is beriberi? +
Beriberi is a disease caused by thiamine deficiency. The wet form affects the heart and circulation, the dry form the nervous system. In countries with fortified foods it is rare and occurs there mainly with excessive alcohol use.
Can a high vitamin B1 value be dangerous? +
According to MedlinePlus, poisoning from too much thiamine is not known. A notable value should still be assessed by a doctor, because high B vitamin levels can also be related to an underlying condition.
Vitamin B1 (thiamine)
Sources
Last updated: October 05, 2026
This information is for orientation only and does not replace medical advice. Reference ranges can vary by laboratory, method and country.