Vitamins · 4 min read ·

Vitamin B1: energy from carbohydrates

The body needs thiamin to get energy from carbohydrates and amino acids. A varied diet usually provides enough; people who drink a lot of alcohol are most at risk.

B1

In a nutshell

1What it does and how much you need

Thiamin is part of the enzymes that release energy from carbohydrates and some amino acids. A deficiency causes beriberi, which mainly affects the nerves and the heart.1

EFSA recommendation 0.1 mg/MJ EFSA recommends 0.1 mg of thiamin for adults per megajoule (about 240 kcal) of energy eaten. Someone eating 2,000 kcal a day needs about 0.84 mg. Adults in Europe take in 0.9–2 mg a day on average.1

2Where to find it

Data 1.9 mg Wheat germ has the most thiamin (1.9 mg per 100 g), followed by flaxseed and sunflower seeds (1.6 and 1.5 mg), oat bran (1.2 mg), pork tenderloin (1 mg) and dry soya beans or lentils (0.9 mg).3

In animal foods thiamin is mostly in the form of phosphates, in plants it is free. In the gut the phosphates are split off and free thiamin is absorbed by a carrier with limited capacity.1

3Forms and absorption

EFSA recommendation 95% In healthy people, over 95% of thiamin is absorbed at usual intakes. Alcohol and some substances in food — certain phenolic compounds, sulphites or thiaminase enzymes — reduce its use.1
Weak evidence — one study 1,500 mg In a study of healthy volunteers, blood thiamin rose with the dose up to 1,500 mg. High levels can therefore be reached quickly even with ordinary thiamine hydrochloride tablets.4
Weak evidence — one study 11× Benfotiamine is a fat-soluble form of thiamin. In a study it raised plasma thiamin about 11 times more than the same dose of thiamine hydrochloride, and its active form in red blood cells about twice as much.5

In the EU, supplements may contain thiamin as the hydrochloride, mononitrate, monophosphate chloride or pyrophosphate chloride; benfotiamine is not among the forms permitted in food supplements.6 EFSA has not set an upper level for thiamin — the data are not sufficient.2

4Who needs more

Weak evidence — Cochrane 2 studies Thiamin has been the standard treatment for Wernicke-Korsakoff syndrome — brain damage from thiamin deficiency, mainly in people who drink a lot of alcohol — for over 50 years. But according to a Cochrane review, there are no studies showing what dose to give and for how long.7
Weak evidence 2.5× A summary of studies: people with heart failure are 2.5 times more often thiamin deficient than others. Small studies suggest supplementation may improve heart function and ease symptoms.8
Weak evidence — a small randomised trial 12 months People with type 2 diabetes and nerve damage took 600 mg of benfotiamine a day or placebo for a year. Their blood thiamin rose, but their nerves did not improve more than with placebo in any of the measures followed.9

An older six-week study of 165 people suggested a slight easing of symptoms with benfotiamine; the result, however, was at the edge of statistical significance.10

What to take from this

Sources

Written on , based on studies available at that date. Newer research may change the conclusions.

  1. EFSA NDA Panel (2016). Dietary reference values for thiamin. EFSA Journal 14:4653. doi.org/10.2903/j.efsa.2016.4653
  2. EFSA (2025). Overview on Tolerable Upper Intake Levels as derived by the Scientific Committee on Food (SCF) and the EFSA Panel on Nutrition (version 11). efsa.europa.eu
  3. USDA ARS (2018). FoodData Central — SR Legacy, thiamin per 100 g: wheat germ 1.9 mg (FDC 168892), flaxseed 1.6 mg (FDC 169414), sunflower seeds 1.5 mg (FDC 170562), oat bran 1.2 mg (FDC 168872), pork tenderloin, raw 1.0 mg (FDC 168249), soybeans, dry 0.9 mg (FDC 174270), lentils, dry 0.9 mg (FDC 172420). fdc.nal.usda.gov
  4. Smithline H. A., Donnino M., Greenblatt D. J. (2012). Pharmacokinetics of high-dose oral thiamine hydrochloride in healthy subjects. BMC Clin Pharmacol 12:4. doi.org/10.1186/1472-6904-12-4
  5. Xie F. et al. (2014). Pharmacokinetic study of benfotiamine and the bioavailability assessment compared to thiamine hydrochloride. J Clin Pharmacol 54:688–695. doi.org/10.1002/jcph.261
  6. Directive 2002/46/EC on food supplements, Annex II — forms of vitamins and minerals permitted in supplements (consolidated version 26 Nov 2025). eur-lex.europa.eu
  7. Day E. et al. (2013). Thiamine for prevention and treatment of Wernicke-Korsakoff syndrome in people who abuse alcohol. Cochrane Database Syst Rev CD004033. doi.org/10.1002/14651858.CD004033.pub3
  8. Jain A. et al. (2015). Determining the role of thiamine deficiency in systolic heart failure: a meta-analysis and systematic review. J Card Fail 21:1000–1007. doi.org/10.1016/j.cardfail.2015.10.005
  9. Ziegler D. et al. (2026). Effects of benfotiamine treatment over 12 months on morphometric, neurophysiological and clinical measures in type 2 diabetes patients with symptomatic polyneuropathy: a randomized, placebo-controlled, double-blind clinical trial (BOND study). BMJ Open Diabetes Res Care 14. doi.org/10.1136/bmjdrc-2025-005773
  10. Stracke H. et al. (2008). Benfotiamine in diabetic polyneuropathy (BENDIP): results of a randomised, double blind, placebo-controlled clinical study. Exp Clin Endocrinol Diabetes 116:600–605. doi.org/10.1055/s-2008-1065351

This is general information and does not replace a doctor. Thiamin deficiency with heavy drinking is a serious condition that needs a doctor.