Vitamin B1 (Thiamine)

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By the Nutriveda editorial team · Updated 5 November 2026

Vitamin B1 (thiamine) is a water-soluble B vitamin that your cells need to turn carbohydrates, fats and protein into energy and to keep nerves working, and the body holds only small amounts, so you need a steady supply from food. EFSA sets the reference intake at 0.1 mg per megajoule of energy for all adults, which works out to about 0.8 mg a day on 2,000 kcal and about 1 mg on 2,500 kcal. Good sources are pork, sunflower seeds, oats, whole-grain bread, peas, beans and lentils. Today deficiency is seen mostly in people who drink too much alcohol.

What vitamin B1 does

In the body thiamine works mainly as thiamine diphosphate (TDP), a helper molecule for five enzymes involved in the metabolism of glucose, amino acids and fats (NIH). An adult carries only about 25-30 mg in total, mostly in the liver, and the vitamin has a short half-life, which is why intake has to be regular. The EU allows these health claims for foods that are at least a source of thiamine (Regulation (EU) 432/2012):

• “Thiamine contributes to normal energy-yielding metabolism”
• “Thiamine contributes to normal functioning of the nervous system”
• “Thiamine contributes to normal psychological function”
• “Thiamine contributes to the normal function of the heart”

How much you need a day

Group	EFSA population reference intake	For reference: NIH RDA (US)
Men, 18+	0.1 mg/MJ	1.2 mg
Women, 18+	0.1 mg/MJ	1.1 mg
Pregnancy	0.1 mg/MJ	1.4 mg
Breastfeeding	0.1 mg/MJ	1.4 mg
Upper limit (UL)	Not set: no adequate data to derive one	Not set

EFSA ties thiamine to energy intake because the vitamin is used to release energy from food: the more you eat, the more you need. To turn the figure into milligrams, multiply your daily energy in MJ by 0.1 (1,000 kcal is 4.184 MJ). On 2,000 kcal that is 0.84 mg, on 2,500 kcal 1.05 mg (our calculation). The NHS gives a practical rule of 1 mg a day for men and 0.8 mg for women aged 19-64.

Best food sources

Food	Thiamine, 100 g	Portion	Per portion
Sunflower seed kernels, dried	1.48 mg	1/4 cup, 35 g	0.52 mg
Pork tenderloin, lean, roasted	0.950 mg	85 g	0.81 mg
Oats	0.763 mg	1/2 cup, 78 g	0.60 mg
Peanuts, raw	0.640 mg	1 oz, 28 g	0.18 mg
Whole-wheat bread	0.394 mg	1 slice, 32 g	0.13 mg
Green peas, raw	0.266 mg	1 cup, 145 g	0.39 mg
Black beans, boiled	0.244 mg	1 cup, 172 g	0.42 mg
Atlantic salmon, farmed, raw	0.207 mg	85 g	0.18 mg
Brown rice, long-grain, cooked	0.178 mg	1 cup, 202 g	0.36 mg
Lentils, boiled	0.169 mg	1 cup, 198 g	0.34 mg

Source: USDA FoodData Central, SR Legacy, checked 5 November 2026: sunflower seeds FDC 170562, pork tenderloin FDC 168250, oats FDC 169705, peanuts FDC 172430, whole-wheat bread FDC 172688, green peas FDC 170419, black beans FDC 173735, salmon FDC 175167, brown rice FDC 169704, lentils FDC 172421. Portions are USDA household measures (1/4 cup and 1/2 cup are calculated from the USDA cup weight); values per portion are calculated and rounded.

A portion of pork or a bowl of oats gives more than half of what most adults need, and a small handful of sunflower seeds about half. If you eat no meat, build your days on whole grains and pulses: whole-wheat bread, brown rice, peas, lentils and beans. Peanuts and salmon add smaller amounts.

Cooking losses. Thiamine dissolves in water, so a good part is lost when the cooking water is thrown away, and heat reduces it: bread has 20-30% less thiamine than its raw ingredients (NIH). Using the cooking liquid of beans and lentils in soups and stews keeps more of it.

Deficiency: signs and who is at risk

Early signs are weight loss, poor appetite, confusion, short-term memory problems, muscle weakness and heart symptoms (NIH). Severe deficiency causes beriberi. Dry beriberi affects the nerves: numbness or tingling in the hands and feet, trouble walking, weakness in the lower legs, confusion. Wet beriberi affects the heart: shortness of breath, fast heart rate and swollen legs (MedlinePlus).

Alcohol is the main risk today. Up to 80% of people with chronic alcohol dependence develop thiamine deficiency (NIH). Heavy drinking worsens nutrition and makes it harder for the body to absorb and store the vitamin (MedlinePlus). The most serious result is Wernicke-Korsakoff syndrome, 8-10 times more common in people with chronic alcohol dependence than in the general population (NIH). Wernicke encephalopathy brings confusion, loss of coordination and abnormal eye movements or double vision; Korsakoff syndrome brings severe memory loss and made-up stories to fill the gaps. Thiamine is given by injection as soon as possible and can improve confusion, vision and coordination, but it often does not reverse the memory loss (MedlinePlus).

Other groups at risk (NIH, MedlinePlus):

• Older adults: up to 20-30% have lab signs of some degree of deficiency.
• People after bariatric (weight-loss) surgery, and people with other forms of malabsorption.
• Severe vomiting in pregnancy (hyperemesis gravidarum).
• People with diabetes, HIV/AIDS or heart failure, and people on dialysis or high-dose diuretics such as furosemide.

Supplements: when they make sense

The most common forms in supplements are thiamine mononitrate and thiamine hydrochloride. Benfotiamine is a synthetic fat-soluble derivative that the body converts to thiamine (NIH). Neither EFSA nor the US Food and Nutrition Board has set an upper limit: no adverse effects have been reported from high intakes, and the body excretes the excess in urine, although the US board still notes that excessive intakes could cause harm. The NHS says 100 mg a day or less from supplements is unlikely to cause harm.

For most people food is enough. Supplements make sense when a doctor recommends them: in alcohol dependence, after bariatric surgery, with long-term diuretics, or when a deficiency is suspected. In suspected Wernicke encephalopathy, treatment is urgent and medical, not a tablet at home.

Who should be careful

• People who drink heavily. For heavy drinkers who cannot stop, thiamine supplements and a good diet may lower the risk of Wernicke-Korsakoff syndrome, but they do not remove it (MedlinePlus). Talk to a doctor.
• Furosemide and other loop diuretics increase thiamine loss in urine and can lower levels (NIH).
• Fluorouracil, a chemotherapy drug, may block the active form of thiamine; case reports link it to beriberi and Wernicke encephalopathy (NIH).
• Bariatric surgery. A 2008 review found 84 cases of Wernicke encephalopathy after such surgery, mostly gastric bypass (NIH). Follow the supplement plan your surgical team gives you.

FAQ

What is vitamin B1 good for?

Thiamine helps your cells release energy from carbohydrates, fat and protein, and it is needed for normal nerve, heart and psychological function. These are the four EU-authorised health claims for thiamine.

Which foods are high in thiamine?

Per 100 g in USDA data, sunflower seeds have 1.48 mg, lean roasted pork tenderloin 0.95 mg and oats 0.76 mg. Whole-wheat bread, peanuts, peas, beans, brown rice and lentils add useful amounts through the day.

Can alcohol cause vitamin B1 deficiency?

Yes. Up to 80% of people with chronic alcohol dependence become deficient, because drinking reduces both intake and absorption. Severe deficiency can cause Wernicke-Korsakoff syndrome, a medical emergency treated with thiamine injections.

Related entries and articles

• Sunflower seeds and peanuts
• Oats, whole-wheat bread and brown rice
• Lentils and peas
• Vitamin B2 (riboflavin) and vitamin B3 (niacin)
• Vitamin B12 and magnesium
• Warm lentil salad with roasted carrots and feta
• Foods for energy without caffeine

Sources

1. EFSA: Summary of Dietary Reference Values, version 4 (September 2017) – thiamin. efsa.europa.eu
2. EFSA: Overview on Tolerable Upper Intake Levels as derived by the Scientific Committee on Food (SCF), version 11 (August 2025). efsa.europa.eu
3. Commission Regulation (EU) No 432/2012 – permitted health claims. legislation.gov.uk
4. NIH Office of Dietary Supplements: Thiamin, Fact Sheet for Health Professionals. ods.od.nih.gov
5. MedlinePlus: Beriberi. medlineplus.gov
6. MedlinePlus: Wernicke-Korsakoff syndrome. medlineplus.gov
7. NHS: Vitamin B. nhs.uk
8. USDA FoodData Central, SR Legacy: Seeds, sunflower seed kernels, dried (FDC 170562); Pork, fresh, loin, tenderloin, separable lean only, cooked, roasted (FDC 168250); Peanuts, all types, raw (FDC 172430). fdc.nal.usda.gov
9. USDA FoodData Central, SR Legacy: Oats (FDC 169705); Bread, whole-wheat, commercially prepared (FDC 172688); Rice, brown, long-grain, cooked (FDC 169704). fdc.nal.usda.gov
10. USDA FoodData Central, SR Legacy: Peas, green, raw (FDC 170419); Beans, black, mature seeds, cooked, boiled (FDC 173735); Lentils, mature seeds, cooked, boiled (FDC 172421); Fish, salmon, Atlantic, farmed, raw (FDC 175167). fdc.nal.usda.gov

This page is for information only and is not medical or dietary advice.