Covered by the diet. In deficiency (alcoholism, bariatric surgery) or specific uses, higher doses under supervision.
Essential treatment of the deficiency, which can be an emergency.
Possible improvement (sometimes as benfotiamine) in diabetic neuropathy.
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Thiamine, or vitamin B1, was the first B vitamin to be identified and chemically isolated (hence its numbering), a historic milestone tied to research on beriberi, a devastating endemic disease in populations that consumed diets based on hulled, refined rice in East Asia during the 19th and 20th centuries; the work of the Dutch physician Christiaan Eijkman in Java (Nobel Prize 1929) and later of the Polish biochemist Casimir Funk (who coined the term "vitamin") established that beriberi was a disease caused by a deficiency of a specific nutritional factor present in the rice husk that processing removed, opening the era of vitamins in clinical nutrition.
The biological function of thiamine is exerted through its phosphorylated form, thiamine pyrophosphate (TPP), a cofactor of several key enzymes of energy metabolism: pyruvate dehydrogenase (entry to the Krebs cycle), alpha-ketoglutarate dehydrogenase (Krebs cycle), transketolase (pentose pathway), and branched-chain ketoacid dehydrogenases (catabolism of leucine, isoleucine, and valine); this central position in carbohydrate metabolism explains why deficiency produces conditions with simultaneous neurological, cardiac, and muscular manifestations.
Clinical thiamine deficiency produces two main conditions: wet beriberi (with cardiac involvement, high-output heart failure, edema, and dyspnea) and dry beriberi (with neurological involvement, peripheral neuropathy, and muscle weakness); in developed populations classic beriberi is extremely rare, but subclinical deficiency can appear in chronic alcoholism (where thiamine is also the first vitamin to be depleted), severe malnutrition, gastrointestinal malabsorption, hyperemesis gravidarum, bariatric surgery, and chronic dialysis.
One of the most critical clinical indications for parenteral thiamine is the prevention and treatment of Wernicke encephalopathy in patients with chronic alcoholism, severe malnutrition, or risk of thiamine deficiency: the classic picture (ophthalmoplegia, ataxia, confusion) can be precipitated by administering intravenous glucose without prior thiamine in people with subclinical deficiency, since glucose dramatically increases thiamine consumption; the standard emergency protocol is to administer thiamine before or simultaneously with any parenteral glucose in at-risk patients, a practice that prevents the transformation of a subclinical deficiency into an irreversible neurological emergency.
In chronic alcoholism, oral or intramuscular thiamine supplementation at high doses during detoxification treatment significantly reduces neurological complications and improves medium-term cognitive prognosis; routinely administering thiamine is standard practice in alcohol detoxification programs.
In type 2 diabetes, and especially in diabetic neuropathy, several studies have shown benefits with benfotiamine (a fat-soluble form of thiamine with significantly higher bioavailability than conventional water-soluble thiamine) at doses of 300-600 mg/day for months, with improvements in neuropathic symptoms and in markers of advanced glycation; benfotiamine is used in Germany and other European countries as a specific supplement for diabetic neuropathy with moderate clinical support.
In heart failure with prolonged diuretic treatment (especially furosemide), subclinical thiamine deficiency is common and may contribute to myocardial dysfunction; thiamine supplementation modestly improves ejection fraction in some small studies, an indication in integrative cardiology with modest clinical support.
Nutritional doses are 1.1-1.2 milligrams daily in adults; for treatment of clinical deficiency, alcoholism, or diabetic neuropathy, doses of 50-100 mg/day orally or high parenteral doses depending on severity; benfotiamine at 300-600 mg/day is used for specific indications with clinical support; conventional thiamine HCl has limited oral bioavailability because of saturation of the intestinal transporter, whereas benfotiamine (fat-soluble) has several-fold higher bioavailability.
It is one of the vitamins with an exceptional safety profile: practically no adverse effects at the usual nutritional and therapeutic doses (even at very high doses no significant toxicities have been described because the excess is efficiently excreted in urine); the most serious risk is the exceptional anaphylactic reactions with parenteral thiamine (especially intravenous), which is why hospital administration follows specific protocols; in pregnancy and breastfeeding the usual nutritional and therapeutic doses are safe and adequate intake is important for fetal and infant development; hyperemesis gravidarum with thiamine depletion is an obstetric emergency that requires immediate supplementation.
Information, not medical advice. Scientific evidence reflects the quality of the studies.