Thiamine is a cofactor for pyruvate dehydrogenase (glucose metabolism) and transketolase (pentose phosphate pathway), so it helps maintain normal energy metabolism.
Severe deficiency is associated with beriberi and, in the setting of chronic alcohol use, with Wernicke-Korsakoff syndrome.
In quiescent inflammatory bowel disease with severe chronic fatigue, 4 weeks of 600 to 1,800 mg/day oral thiamine was associated with reduced fatigue scores, while 300 mg/day for 12 weeks did not maintain that reduction.
Benfotiamine, described in one trial as allithiamine, is a lipid-soluble thiamine prodrug reported to have high bioavailability, and it is the form used in the diabetic polyneuropathy trials below.
Metformin inhibits the intestinal thiamine transporter ThTR-2 in laboratory assays, and diuretic use is among the mechanisms proposed for low thiamine status in heart failure.
US RDA: 1.1 mg/day for women and 1.2 mg/day for men.