Thiamine (vitamin B1)
A water-soluble vitamin at the centre of energy metabolism, often taken for tiredness.
- Tiredness and energy
- Nerve symptoms
- Blood sugar
- Memory and thinking
A plain-English overview, not advice. Written from published reviews and trials and from what people say in public forums.
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On this page
What is thiamine (vitamin B1)?
Thiamine, or vitamin B1, is a water-soluble vitamin the body cannot make for itself: only bacteria, fungi and plants build it, so it has to come from food or from a capsule. Inside the body it works as a helper molecule for a set of enzymes, most of them sitting in mitochondria, that release energy from carbohydrate and amino acids, and others that belong to the body’s antioxidant chemistry. A shortfall can follow poor intake, a raised requirement, heavy losses, or long-term heavy drinking. On a UK shelf it appears either as plain thiamine, usually the hydrochloride or the mononitrate salt, or as benfotiamine.
Why do people take thiamine (vitamin B1)?
Tiredness and energy
The thinking. Thiamine’s day job is energy metabolism: the enzymes that depend on it sit inside mitochondria, where carbohydrate is broken down into the fuel cells actually spend. People who feel flat or worn down reach for it on the strength of that, which is why vitamin B1 turns up in so many energy formulas.
What research has found. Two trials measured chronic fatigue in adults whose inflammatory bowel disease was quiet. Four weeks of a very high dose, 600 to 1,800 mg a day, lowered fatigue scores by four and a half points while placebo drifted the other way; 300 mg a day over the twelve weeks afterwards made no clear difference. Studies here point in different directions, so this one is still being worked out; the dose, how long people took it and who took part all seem to matter.
Nerve symptoms
The thinking. Tingling, numbness and burning in the hands and feet send a lot of people towards the B vitamins, and thiamine has a long association with the nerves: when it runs short, the peripheral nerves are among the systems affected, alongside the brain, heart, muscle and gut. Benfotiamine, the fat-soluble form on the shelf beside plain thiamine, is bought with this in mind.
What research has found. One trial followed 67 adults with type 1 diabetes taking 300 mg of benfotiamine a day for two years. Whole-blood thiamine rose sharply, but the measures of nerve function, and the inflammatory markers taken alongside them, changed no differently from placebo. Few studies have measured this yet, so there is little to go on either way.
Blood sugar
The thinking. Thiamine sits in the chemistry that handles carbohydrate, and reviews describe thiamine running low in people with type 1 and type 2 diabetes. That has made it, and benfotiamine especially, a familiar buy among people keeping an eye on their blood sugar.
What research has found. Six trials in 364 adults with type 2 diabetes were pooled: doses from 100 to 900 mg a day, of either form, left HbA1c, the longer-run measure of blood sugar, and fasting glucose no different from placebo, though HDL rose slightly and one benfotiamine dose lowered triglycerides. A small crossover trial in twelve adults with raised blood sugar did see two-hour glucose fall. The studies disagree, so this is unsettled: dose, duration and who took part all seem to shift the result.
Memory and thinking
The thinking. The brain leans hard on the energy chemistry thiamine makes possible, and reviews list confusion, reduced memory and disturbed sleep among the milder signs of it running short. That link is what puts thiamine, and benfotiamine, in front of people thinking about how sharp they feel.
What research has found. One twelve-month trial gave benfotiamine or a placebo to adults with mild memory problems or early dementia. On the main test, where a rising score means more decline, the rise was smaller in the benfotiamine group, though not by a statistically clear margin; a separate rating of everyday function did separate the groups, as did a blood marker of sugar-damaged proteins. Very little research has measured this so far, either way.
What does thiamine (vitamin B1) do in the body?
Thiamine is a helper, not a fuel. The body turns it into thiamine diphosphate, which clips into a small set of enzymes - pyruvate dehydrogenase, 2-oxoglutarate dehydrogenase and transketolase among them - and without it those enzymes cannot do their work. They sit where carbohydrate and amino acids are broken down for energy, most of them inside mitochondria, the parts of a cell that make its ATP.
That narrow job explains the wide reach. The tissues that burn the most fuel notice a shortfall first, which is why the brain, the heart and the nerves dominate the descriptions of thiamine running low, from confusion and poor memory through to serious illness. Some thiamine-dependent enzymes also belong to the body’s antioxidant chemistry, and laboratory work ties a shortfall to oxidative stress in the brain. Absorption runs by two routes, one that saturates and one that does not, so blood levels climb quickly after a large dose but not in proportion to it.
What do people say about taking thiamine (vitamin B1)?
These are anecdotes people have shared, not evidence.
What people like
- These threads come from only two places, a chronic fatigue community and a diabetes community, so the reasons discussed are narrower than the shelf is.
- In the fatigue threads, steadier energy is what people describe noticing, with clearer thinking and sometimes longer sleep mentioned alongside it.
- In the diabetes threads several describe nerve pain in the feet, or after shingles, easing, and a couple of them say it happened within days.
- Blood sugar comes up in the diabetes threads too, with a couple of people describing their readings drifting down over several weeks.
Common complaints
- Several report little or nothing after weeks of it: no clear change in energy, in thinking, or in what they bought it for.
- Side effects described include pins and needles at the higher doses, dry or watering eyes with light sensitivity, and restless, broken sleep.
- Nobody agrees on a dose. The amounts people quote at each other run from about 20 mg a day to 2,000 mg.
- Several are openly unconvinced, pointing at how few human trials there are and at the claims made about how well it absorbs.
How people take it
- The doses described run from 25 mg a day to well over 1,000 mg, and the larger ones are usually split across the day.
- Several arrived at their dose by trial and error, moving up or down from where they started until the side effects settled.
- Fat-soluble forms are favoured by people chasing absorption, and by all of the diabetes threads; plain thiamine hydrochloride is what the rest take.
- It rarely goes in alone: magnesium, B12 or another B vitamin sits beside it in most of the routines described.
Read from these public discussions:
- High dose vitamin B1 (thiamine) (Phoenix Rising ME/CFS forums, 2014)
- Thiamin (Vitamin B1) supplements (Phoenix Rising ME/CFS forums, 2019)
- Benfotiamine (Diabetes.co.uk forum, 2009)
- Benfotiamine and/or vitamin supplements for neuropathy (Diabetes.co.uk forum, 2012)
- Benfotiamine (fat soluble vitamin B1) (Diabetes.co.uk forum, 2024)
What forms of thiamine (vitamin B1) are there?
| Form | What’s different | Per serving, on products we list |
|---|---|---|
| Thiamine | The vitamin itself, water-soluble, sold as the hydrochloride or the mononitrate salt. | 100 mg |
| Benfotiamine | A fat-soluble derivative of thiamine; the label states milligrams of benfotiamine, not of thiamine. | not in our price tables yet |
What else is worth knowing about thiamine (vitamin B1)?
- Labels give the thiamine per serving, and a serving may be more than one tablet. Plain thiamine is sold as the hydrochloride or the mononitrate salt; benfotiamine is a fat-soluble derivative and its label states milligrams of benfotiamine.
- The amounts used in trials spanned a huge range: 1.2 mg a day in one supplementation study, 100 to 900 mg a day in the blood sugar trials, and 600 to 1,800 mg a day for four weeks in the fatigue trial.
- Side effects reported in the trials were mild. In a benfotiamine safety study the rate of side effects matched placebo, with a raised liver enzyme and white cells in the urine the ones noted most often.
- Most of this research was done in a hospital or a clinic, and in people already living with something - type 1 or type 2 diabetes, inflammatory bowel disease, early memory loss, heart failure, critical illness - rather than in healthy adults.
If you take medication, are pregnant, or have a health condition, check with a pharmacist or GP first.
The research behind this page (13 studies)
- Long-term maintenance treatment with 300 mg thiamine for fatigue in patients with inflammatory bowel disease: results from an open-label extension of the TARIF study. (2022, randomised trial)
- Randomised clinical trial: high-dose oral thiamine versus placebo for chronic fatigue in patients with quiescent inflammatory bowel disease. (2021, randomised trial)
- The effects of long-term oral benfotiamine supplementation on peripheral nerve function and inflammatory markers in patients with type 1 diabetes: a 24-month, double-blind, randomized, placebo-controlled trial. (2012, randomised trial)
- A Systematic Review of Thiamine Supplementation in Improving Diabetes and Its Related Cardiovascular Dysfunction. (2025, systematic review)
- Effect of thiamine supplementation on glycaemic outcomes in adults with type 2 diabetes: a systematic review and meta-analysis. (2022, meta-analysis)
- High-dose thiamine supplementation improves glucose tolerance in hyperglycemic individuals: a randomized, double-blind cross-over trial. (2013, randomised trial)
- Benfotiamine and Cognitive Decline in Alzheimer's Disease: Results of a Randomized Placebo-Controlled Phase IIa Clinical Trial. (2020, randomised trial)
- Neurological, Psychiatric, and Biochemical Aspects of Thiamine Deficiency in Children and Adults. (2019, review)
- Genetic defects of thiamine transport and metabolism: A review of clinical phenotypes, genetics, and functional studies. (2019, review)
- Thiamine Deficiency and Neurodegeneration: the Interplay Among Oxidative Stress, Endoplasmic Reticulum Stress, and Autophagy. (2017, review)
- Thiamine and Cardiovascular Disease: A Literature Review. (2018, review)
- Thiamine deficiency and cardiovascular disorders. (2018, review)
- Thiamine and selected thiamine antivitamins - biological activity and methods of synthesis. (2018, review)
How much does thiamine (vitamin B1) cost?
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