Vitamin B1 (Thiamin)

Thiamin is one of the eight B vitamins. Its main job is helping enzymes convert carbohydrates and amino acids into energy the body can use. It also supports nerve function, particularly in the brain. The body holds very little thiamin in reserve, which is why a steady supply from food matters.

In the UK, dietary thiamin deficiency is essentially absent in the general population. The exception, well-documented in NHS clinical practice, is chronic heavy alcohol use, which reduces thiamin absorption and increases urinary loss. Severe deficiency in this context causes Wernicke-Korsakoff syndrome, a serious brain condition; admission to A&E with this picture is treated with high-dose thiamin injections before symptoms progress.

Values per 100g from USDA SR Legacy and McCance and Widdowson 7th edition; the site's food entries currently store macros only.

Wholemeal bread, brown rice, and pulses across the week comfortably cover the requirement on a UK plant-light or plant-heavy diet alike.

UK Reference Nutrient Intake (RNI) for thiamin is set by SACN (1991 Dietary Reference Values).

Thiamin requirement scales with energy intake (SACN's value is 0.4mg per 1,000 kcal), so people with high energy needs may need a little more.

Thiamin deficiency is rare in the UK general population. It is seen mainly in chronic heavy alcohol use, severe malnutrition, hyperemesis gravidarum (severe pregnancy sickness), and after some bariatric surgery.

Early signs: fatigue, irritability, poor appetite. Established deficiency causes beriberi (heart failure and nerve problems) or Wernicke's encephalopathy (confusion, eye movement problems, balance problems). Wernicke's untreated progresses to Korsakoff syndrome (severe memory loss).

At higher risk in the UK

• People with alcohol dependence (the dominant UK risk).
• People with severe pregnancy sickness or eating disorders.
• People after some types of bariatric surgery.
• People on long-term dialysis.

Suspected acute Wernicke-Korsakoff is a medical emergency and is treated with parenteral thiamin in hospital.

Thiamin from food is not a realistic concern; the body excretes the excess in urine.

NHS supplement guidance: taking 100mg or less a day of thiamin in supplements is unlikely to cause any harm.

Routine thiamin supplementation is not needed for healthy adults eating any mixed UK diet. Treatment doses are used in confirmed deficiency, alcohol-dependence support, and some absorption conditions, under medical supervision.

Thiamin is in most UK multivitamin and B-complex products. There is no benefit to high doses for general health.

• The B-vitamin family: Vitamin B2, Vitamin B3, Vitamin B6, Folate, Vitamin B12.
• Best food sources: Pork, Oat bran, Lentils, Peanuts.

• NHS. Vitamins and minerals: Vitamins B. nhs.uk/conditions/vitamins-and-minerals/vitamin-b.
• SACN. Dietary Reference Values for Food Energy and Nutrients for the United Kingdom. Department of Health Report 41 (1991).
• Public Health England. McCance and Widdowson's The Composition of Foods, 7th summary edition (2015).

This page is reference information for UK shoppers. It is not medical advice.