Micronutrient, Vitamin B1 (Thiamine), Blood

Vitamin B1, also called thiamine, is a nutrient your body needs to convert food into energy and to keep your nerves and heart working properly. This blood test measures how much thiamine is stored in your red blood cells, which gives a more accurate picture of your body's thiamine levels than a simple blood serum test. Because your body cannot make thiamine on its own and stores only a small amount, levels can drop if you are not eating enough, have difficulty absorbing nutrients, or drink alcohol heavily. Low thiamine can cause serious problems with the nervous system and heart, but these are often reversible when caught early. Your healthcare provider will interpret your result alongside your symptoms and overall health history.

When elevated: Elevated blood thiamine levels are generally not associated with toxicity, as excess water-soluble thiamine is renally excreted; however, markedly elevated levels may reflect recent supplementation or high-dose therapeutic administration rather than a pathological state. When low: Low blood thiamine levels indicate depleted tissue stores and are associated with risk of deficiency syndromes including peripheral neuropathy (dry beriberi), high-output cardiac failure (wet beriberi), and Wernicke encephalopathy or Wernicke-Korsakoff syndrome, which can cause permanent neurological impairment if not addressed promptly.

Thiamine supports carbohydrate metabolism and ATP production during intense training, making it important for endurance athletes and high-volume trainers. Increased caloric expenditure and carb intake can raise thiamine demands; inadequate intake or heavy sweating may contribute to deficiency that impairs energy metabolism and recovery. Testing may help identify a correctable cause of unexplained fatigue or performance plateau in athletes with marginal nutritional intake.