Vitamin B1 (Thiamine)

Thiamine is a water-soluble B vitamin and, as thiamine pyrophosphate, the required cofactor for pyruvate dehydrogenase, alpha-ketoglutarate dehydrogenase and transketolase. Without it, glucose cannot be fully oxidised, and the tissues that suffer first are those most dependent on aerobic glucose metabolism: the brain and the heart.

Body stores last only two to three weeks, which is why deficiency appears faster than with most vitamins. Classic beriberi is rare in high-income countries, but subclinical deficiency is not: it is documented in chronic alcohol use, after bariatric surgery, in heart failure treated with loop diuretics, in hyperemesis of pregnancy and in people with diabetes, who lose thiamine renally at up to 15 times the normal rate. Wernicke encephalopathy — confusion, eye signs and ataxia — is a medical emergency treated with parenteral thiamine, never oral supplements.

For people without deficiency risk, supplemental thiamine has little to offer. High-dose benfotiamine has been studied in diabetic neuropathy with mixed but generally favourable short-term results, and thiamine has been trialled in heart failure with diuretic use, where correcting a deficit improves ejection fraction.