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Strong evidence19 studies

How we rate

“Strong” = several concordant meta-analyses or systematic reviews. “Moderate” = one synthesis, or several controlled trials. “Limited” = early trials only. The rating is about the quality of the studies, not about how useful the supplement is.

Thiamine (vitamin B1)

Vitamin B1. As a dietary supplement, it has mainly been tested on sick people: less fatigue at very high doses in an inflammatory bowel disease, slightly lower blood glucose in a small trial; nothing on heart failure in two meta-analyses, and it does not repel mosquitoes.

Benefits

Fatigue from inflammatory bowel disease: in patients in remission, 600 to 1,800 mg per day markedly reduced chronic fatigue compared to the placebo.
Blood glucose: in 12 hyperglycemic people, 3 daily doses of 100 mg lowered glucose measured 2 hours after a sugar load; diastolic and mean blood pressure also dropped in six weeks.
Diabetic kidneys: 3 daily doses of 100 mg for three months reduced urinary albumin, an early marker of kidney damage, in type 2 diabetics.
Depression, in addition to treatment: in 51 hospitalized patients, thiamine added to standard treatment reduced symptoms faster than the placebo at 6 weeks.
Stress and sleep, with vitamin B2: 100 mg of B1 and 100 mg of B2 per day for four weeks reduced perceived stress and sleepiness and improved sleep (43 participants), with no effect on anxiety.
Breastfeeding in a deficiency area: in Cambodia, 1.2 mg per day were enough to raise breast milk thiamine to the level of healthy mothers.

Precautions

Tolerance: up to 1,800 mg per day, thiamine was well tolerated in trials on fatigue, like 500 mg per day for 90 days in elderly people. Heart failure: it does not replace treatment. Two meta-analyses (six and seven trials) find no effect on ejection fraction or on the 6-minute walk test; only heart rate and thiamine status improve. Thiamine deficiency is more frequent in heart failure patients and in diabetics. Limitations: most positive trials are small (9 to 51 people). In dialysis, 250 mg per day with vitamin B6 changed nothing for oxidative stress or inflammation; against fatigue from a liver disease (primary biliary cholangitis), 600 to 1,800 mg per day did no better than the placebo; 200 mg per day for 7 days did not change the progression of heart failure in elderly patients; and thiamine does not repel insects.

Recommended dosage

1.2 mg per day to correct a low intake; 100 to 300 mg per day in most trials, up to 1,800 mg against fatigue.

How to take it

For whom: almost all trials in this sheet involve sick people (diabetes, heart failure, inflammatory bowel disease, depression, dialysis) or mothers in a deficiency area, none on healthy athletes.
Low intake: in Cambodia, 1.2 mg per day raised breast milk thiamine as much as 2.4 or 10 mg.
Blood glucose and blood pressure: 3 daily doses of 100 mg for six weeks, in only 12 people.
Fatigue: 600 to 1,800 mg per day in patients with inflammatory bowel disease; 300 mg per day for 12 weeks did not maintain the effect.
Form: thiamine mononitrate was tested at 500 mg per day for 90 days in elderly heart failure patients.
Time of day: no study in this sheet compares morning and evening, nor intake with or without meals.

Did you know?

Swallowing vitamin B1 to stop getting bitten: the idea has been circulating for a long time, but a 2022 review concludes that thiamine, regardless of the dose or how it is taken, does not repel insects. Controlled experiments have found no effect; only its effect on the annoyance of bites is not ruled out.

What the studies say

This meta-analysis pooled seven randomized controlled trials to evaluate the efficacy of thiamine supplementation in patients with chronic heart failure. The results showed no significant effect of thiamine on measures like left ventricular ejection fraction or the 6-minute walk test. However, supplementation effectively improved thiamine deficiency status. The authors conclude that thiamine has no direct therapeutic effect on heart failure, apart from correcting a deficiency.
He S, Wang S, Xu T, Wang S, Qi M, Chen Q, Lin L, Wu H, Gan P. — Clinical cardiology (2024) — View the source study

For information only: not a substitute for medical advice. Dietary supplements are not a replacement for a varied, balanced diet. Learn more