Key points
B1 is needed for energy and nerves. Thiamine helps enzymes process carbohydrates; a severe shortage leads to beriberi and Wernicke–Korsakoff syndrome, which damages the brain (Institute of Medicine DRI Report 1998. PMID 23193625).
B1 treats Wernicke encephalopathy. It is an emergency; thiamine is given as soon as it is suspected — 200 mg 3 times a day, preferably intravenously (Galvin R Eur J Neurol 2010. PMID 20642790).
Benfotiamine is absorbed better. This fat-soluble form gave on average about 11 times more thiamine in plasma than ordinary tablets (Xie F J Clin Pharmacol 2014. PMID 24399744).
Short courses eased symptoms. Over 3 weeks (40 people) symptoms and pain decreased more than on placebo (Haupt E Int J Clin Pharmacol Ther 2005. PMID 15726875); in BENDIP, a trial of benfotiamine in diabetic polyneuropathy, the main measure improved only in the per-protocol analysis, and the total symptom score, including pain, did not differ from placebo (Stracke H Exp Clin Endocrinol Diabetes 2008. PMID 18473286).
Long courses showed no effect. Over 12 and 24 months benfotiamine did not differ from placebo in nerve function and structure; in the 24-month trial most participants had no symptoms of neuropathy (Ziegler D BMJ Open Diabetes Res Care 2026. PMID 41571333; Fraser DA Diabetes Care 2012. PMID 22446172).
Why the body needs B1
Vitamin B1 (thiamine) works mainly as thiamine pyrophosphate (thiamine diphosphate), a helper of the enzymes that process carbohydrates. The recommended intake for adults is 1.2 mg a day for men and 1.1 mg for women; in the US people usually get about 2 mg from food (Institute of Medicine DRI Report 1998. PMID 23193625). Burgerstein’s handbook, on which this series is based, has no separate chapter on B1 (Burgerstein, Handbuch Nährstoffe 2015, p. 2–4).
Who runs short of B1
Alcohol. In developed countries a B1 shortage is most often found in chronic alcohol misuse (Institute of Medicine DRI Report 1998. PMID 23193625); Wernicke encephalopathy is also more common in these people (Galvin R Eur J Neurol 2010. PMID 20642790).
Bariatric surgery. In a meta-analysis of 41 studies, 7% of people had B1 deficiency even before weight-loss surgery, 19% 3 months after it (an imprecise estimate: 0–68%), and 6% a year after it (Karimi Behnagh A Obes Surg 2024. PMID 38095772). European guidelines advise monitoring B1 for at least 6 months after surgery (Galvin R Eur J Neurol 2010. PMID 20642790).
Heart failure. In a systematic review of 54 studies, B1 deficiency was more common in heart failure: the odds were 2.53 times higher. Possible causes are diuretics and changes in diet and absorption. Small studies suggest that B1 may improve the ejection fraction (the strength of the heart’s contraction) and reduce symptoms, but this needs further study (Jain A J Card Fail 2015. PMID 26497757).
Diabetes. In a small study (26 people with type 1 diabetes, 48 with type 2 and 20 healthy people) plasma thiamine in diabetes was about 75% lower than in healthy people, and the kidneys removed it 16–24 times more actively (Thornalley PJ Diabetologia 2007. PMID 17676306).
Wernicke encephalopathy in plain words
It is acute brain damage caused by a lack of B1. It can be prevented and cured, but it often goes unrecognised during life. In people who misuse alcohol it is suspected when two of four signs are present: undernutrition, eye signs, poor coordination, confusion or mild memory problems (Galvin R Eur J Neurol 2010. PMID 20642790).
What doctors do. Blood for thiamine is taken before the first dose, but treatment starts as soon as it is suspected: 200 mg 3 times a day, preferably intravenously, and before any carbohydrates, including glucose. Thiamine injections are recommended for all at-risk people admitted to the emergency department (Galvin R Eur J Neurol 2010. PMID 20642790).
Benfotiamine: how it differs
Benfotiamine is a fat-soluble precursor of thiamine: in the body it is converted into ordinary thiamine. In healthy volunteers, compared with thiamine hydrochloride tablets, plasma thiamine was on average about 11 times higher, with a wide spread (1147 ± 490%) (Xie F J Clin Pharmacol 2014. PMID 24399744).
Does benfotiamine help nerves in diabetes
Short courses. In BEDIP, a pilot trial of benfotiamine in diabetic polyneuropathy, 40 people with diabetes and neuropathy of no more than 2 years received 400 mg of benfotiamine a day or placebo for 3 weeks. The neuropathy score improved significantly more, and pain decreased the most; the tuning fork test did not change (Haupt E Int J Clin Pharmacol Ther 2005. PMID 15726875).
BENDIP. 165 people with diabetic polyneuropathy received 600 or 300 mg of benfotiamine a day or placebo for 6 weeks. The main measure, the neuropathy symptom score, improved significantly only in the per-protocol analysis (124 people), and among the 133 of 165 participants included in the analysis it narrowly missed significance. The total symptom score, including pain, did not differ from placebo (Stracke H Exp Clin Endocrinol Diabetes 2008. PMID 18473286).
Long courses. In 67 people with type 1 diabetes, mostly without symptoms of neuropathy (probable neuropathy in 16%), 300 mg a day for 24 months did not change nerve function compared with placebo (Fraser DA Diabetes Care 2012. PMID 22446172). In the BOND trial, 57 people with type 2 diabetes and mild or moderate neuropathy received 600 mg a day or placebo for 12 months. The main measure, the length of corneal nerve fibres in the eye, did not differ, nor did the other nerve measures and quality of life (Ziegler D BMJ Open Diabetes Res Care 2026. PMID 41571333).
What the studies showed
| What was tested | Who took part | Result |
|---|---|---|
| Benfotiamine vs thiamine tablets, 2014 | Healthy volunteers | On average about 11 times more thiamine in plasma, with a wide spread (1147 ± 490%) |
| BEDIP, 400 mg a day for 3 weeks, 2005 | 40 people with diabetic neuropathy | Neuropathy score and pain decreased more than on placebo |
| BENDIP, 300 or 600 mg a day for 6 weeks, 2008 | 165 people, 133 in the analysis | Main measure improved only in the per-protocol analysis; total symptom score as on placebo |
| 300 mg a day for 24 months, 2012 | 67 people with type 1 diabetes, mostly without symptoms of neuropathy | Nerve function as on placebo |
| BOND, 600 mg a day for 12 months, 2026 | 57 people with type 2 diabetes | Corneal nerve fibres and other measures as on placebo |
Long courses showed no significant effect on the nerves: this does not prove that there is no benefit, but there is no confirmation of benefit yet (Ziegler D BMJ Open Diabetes Res Care 2026. PMID 41571333; Fraser DA Diabetes Care 2012. PMID 22446172).
Safety
The US Institute of Medicine did not set a safe upper level for B1: it could not estimate at what dose harm begins — there are not enough data. No harmful effects of excess thiamine from food and supplements have been described, although this does not yet prove that any dose is safe (Institute of Medicine DRI Report 1998. PMID 23193625). European neurologists rate the safety of thiamine as very good (Galvin R Eur J Neurol 2010. PMID 20642790); in 57 people with type 2 diabetes taking 600 mg of benfotiamine a day for a year, there were no more adverse events than on placebo (Ziegler D BMJ Open Diabetes Res Care 2026. PMID 41571333).
Who should be more careful
- With alcohol misuse: confusion, unsteadiness or odd changes in vision are a reason to call an ambulance, not to take tablets at home.
- After bariatric surgery: discuss B1 monitoring with your doctor, especially in the first months and during pregnancy (Karimi Behnagh A Obes Surg 2024. PMID 38095772).
- With heart failure (one possible cause of a B1 shortage is diuretics): discuss B1 with your cardiologist (Jain A J Card Fail 2015. PMID 26497757).
- With diabetes and tingling or numbness in the feet: benfotiamine does not replace treatment by a doctor. A B12 deficiency causes similar symptoms — see the article on B12 deficiency.
- When taking B-complex products: they usually contain B6, and an excess of it harms the nerves — see the article on vitamin B6.
Bottom line
A B1 shortage is more common with alcohol misuse, after bariatric surgery and in heart failure, and in diabetes plasma thiamine levels are often low. Wernicke encephalopathy is an emergency treated with intravenous thiamine. Benfotiamine is absorbed better and in a short trial eased neuropathy symptoms, but over 12–24 months it showed no significant effect on the nerves. You can discuss whether you need B1 at a consultation.
This material is for information only and does not replace a doctor’s consultation. The dose and form of vitamin B1 are chosen by a doctor based on the results of an examination.
