Vitamin B1 (Thiamine) Blood Test: Normal Ranges, Causes & What Your Results Mean

What Is Vitamin B1 (Thiamine)?

Vitamin B1, also known as thiamine, is an essential water-soluble vitamin that plays a critical role in energy metabolism. It acts as a coenzyme in the conversion of carbohydrates into energy, making it fundamental to the function of every cell in your body. The brain and nervous system are particularly dependent on thiamine because they rely almost exclusively on glucose for fuel.

Since the body cannot produce thiamine and stores are limited (lasting only 2–3 weeks), a regular dietary intake is essential. Thiamine deficiency can develop surprisingly quickly and has serious neurological and cardiovascular consequences if left untreated.

Why Is Vitamin B1 Tested?

• Investigate symptoms of thiamine deficiency: fatigue, irritability, poor memory, tingling in extremities
• Assess nutritional status in patients with alcohol use disorder — the most common cause of deficiency in the UK
• Evaluate patients with unexplained peripheral neuropathy or cognitive decline
• Monitor patients on long-term diuretics, dialysis, or parenteral nutrition
• Investigate heart failure that may be related to wet beriberi (thiamine-deficient cardiomyopathy)
• Screen patients after bariatric surgery, who are at high risk of B vitamin deficiencies

Normal Ranges

TDP (the active form) in whole blood is the preferred test. Serum thiamine is less reliable as it reflects recent intake rather than tissue stores.

Causes of Low Vitamin B1

• Alcohol use disorder: Alcohol impairs thiamine absorption, reduces liver storage, and increases urinary excretion
• Poor dietary intake: Highly processed diets, eating disorders, or prolonged fasting
• Malabsorption: Coeliac disease, Crohn's disease, chronic diarrhoea, or short bowel syndrome
• Bariatric surgery: Reduced stomach capacity and altered absorption pathways
• Pregnancy: Increased metabolic demand, especially with hyperemesis gravidarum
• Medications: Loop diuretics (furosemide), metformin, and some chemotherapy agents
• Chronic kidney disease: Dialysis removes water-soluble vitamins including thiamine
• High carbohydrate intake without adequate thiamine: Thiamine demand increases with carbohydrate metabolism

Causes of High Vitamin B1

Elevated thiamine levels are rare and generally not clinically significant, as excess is readily excreted in urine. However, very high levels may be seen with:

• Excessive supplementation (megadose B-complex vitamins)
• Recent thiamine injection (parenteral administration)

How to Maintain Healthy Vitamin B1 Levels

• Eat thiamine-rich foods: Whole grains, pork, fortified cereals, legumes, nuts, and seeds
• Choose whole grains over refined: Milling removes up to 80% of thiamine from grains
• Limit alcohol: Even moderate drinking can impair thiamine absorption over time
• Consider supplementation if at risk: B-complex supplements provide 1–5mg thiamine daily
• Cook mindfully: Thiamine is heat-sensitive and water-soluble — steaming or microwaving preserves more than boiling
• Monitor after surgery: Post-bariatric patients should supplement indefinitely

When Should You Get Tested?

• You experience unexplained fatigue, brain fog, or peripheral neuropathy
• You consume alcohol regularly or heavily
• You have had bariatric surgery or have a malabsorption condition
• You follow a very restrictive diet or have an eating disorder
• You are on long-term diuretics or dialysis
• You have unexplained heart failure or cardiomyopathy

Which Lola Health Tests Include Vitamin B1?

• Peak Insights — our most comprehensive panel including B vitamins and 70+ biomarkers