Vitamin B1 (thiamin).

What the nutrient does

Thiamin helps enzymes release energy from food and supports normal growth and cellular function, including nervous-system function.1

Food and deficiency

Thiamin occurs in whole grains, pork, fish and beans; some cereals and breads are enriched or fortified. Processing and cooking can affect the amount present. Prolonged inadequate intake or impaired absorption can cause thiamin deficiency. Risk can be higher with alcohol use disorder, some illnesses or after bariatric surgery. Serious deficiency requires clinical assessment and treatment. Some medicines can also affect thiamin status: NIH notes lower levels associated with the diuretic furosemide and reports of deficiency with the cancer drug fluorouracil. This does not mean everyone taking them is deficient or needs a supplement; discuss concerns with the treating clinician and do not stop prescribed treatment on your own.31

NIH also identifies older adults and people with HIV or diabetes among groups who may have difficulty getting enough thiamin; belonging to a group does not establish an individual deficiency. Blood thiamin levels alone are not reliable indicators of status. A clinician can assess the person’s history and appropriate tests; urgent symptoms should not wait for test results.1

For dietary context, US recommendations for adults are 1.2 mg daily for men and 1.1 mg for women, and 1.4 mg during pregnancy or breastfeeding. These are total daily intake references, not individual supplement doses or treatment instructions.1

When can thiamin deficiency become an emergency?

Severe thiamin deficiency can affect the heart and nervous system. One serious brain condition associated with deficiency is Wernicke encephalopathy, which can involve confusion, difficulty walking or abnormal eye movements. It can occur in people with alcohol dependence but also in other situations involving malnutrition or impaired absorption, including after bariatric surgery. These symptoms have other possible causes and cannot diagnose a deficiency. Sudden confusion requires emergency medical assessment whatever the cause; do not wait for a supplement to work. Clinicians decide on appropriate tests and treatment.1324

The signs do not have to occur together: a person with Wernicke encephalopathy may not have the full set of confusion, walking difficulty and eye movement problems. Do not wait for all three before seeking help. Prolonged vomiting and poor intake can also raise concern about nutrition, including thiamin, without proving a deficiency. If vomiting continues after weight-loss surgery, contact the surgical team or clinician; during pregnancy, frequent vomiting with inability to keep food down warrants contacting a midwife, doctor or hospital as soon as possible. Vomiting has many causes, and these situations need assessment beyond a vitamin supplement.456

What a supplement claim needs to show

Thiamin is needed for normal metabolism, but the fact that it helps release energy from food does not establish that extra thiamin improves energy in someone with adequate status. Compare products using the supplement label guide and discuss personal concerns with a qualified professional.1