- Low vitamin B1 is linked to sleeping too long (9+ hours) — which is just as problematic as sleeping too little
- B1 helps your brain produce the chemicals it needs to regulate when you feel sleepy and when you feel alert
- A 2025 clinical trial found B1 and B2 supplementation improved sleep quality scores and reduced daytime tiredness
- People most at risk of low B1: heavy drinkers, people on restrictive diets, older adults, and those under chronic stress
- You can get enough B1 from food — supplements are most useful if you have reason to suspect you're deficient
What vitamin B1 actually does
Thiamine (vitamin B1) is a water-soluble vitamin your body can't make on its own — you have to get it from food every day. It's essential for converting carbohydrates into energy, and for keeping your nervous system running properly. Without enough of it, your brain's ability to generate energy and maintain the chemical balance needed for sleep starts to break down.
The sleep connection is indirect but real. B1 is involved in making acetylcholine — a neurotransmitter that activates the parasympathetic nervous system, the "rest and digest" mode your body needs to fall and stay asleep. It also plays a role in regulating glutamate in the brain, which affects your sleep-wake rhythm. Animal studies have shown that thiamine influences diurnal rhythms — including body temperature and the sleep-wake cycle — depending on when it's taken.
What the studies show
A 2022 study published in the Journal of Preventive Medicine and Public Health used data from over 100,000 Koreans in the National Health and Nutrition Examination Survey. It found a clear, dose-dependent relationship: people with the lowest thiamine intake were significantly more likely to sleep 9 hours or more per night. Sleeping too long is not simply a sign of laziness — it's associated with the same cardiovascular and metabolic risks as sleeping too little, and often signals that sleep quality is poor even if duration is long.
The association was particularly strong in men and in people who also drank alcohol regularly — a pattern that makes biological sense, since alcohol is one of the main things that depletes thiamine in the body.
A more recent 2025 randomised controlled trial from Macau University of Science and Technology tested B1 and B2 supplementation directly against a placebo in young adults. The group taking the vitamins showed meaningful improvements in Pittsburgh Sleep Quality Index scores and reported less daytime sleepiness — though the study's authors noted the effect on anxiety specifically was not significant, suggesting the sleep benefit may work through stress and nervous system regulation rather than anxiety reduction directly.
Who is most likely to be low in B1
Unlike magnesium, which large proportions of adults are genuinely deficient in, outright thiamine deficiency is relatively uncommon in people eating a varied diet. But suboptimal levels — not low enough to cause the severe neurological condition called Wernicke encephalopathy, but low enough to affect how your brain functions day to day — are more common than most people realise. The groups most at risk are:
Heavy drinkers — alcohol directly blocks the absorption of thiamine in the gut and increases how fast the body loses it. This is the most significant risk factor in Western populations. People on very restricted diets — particularly low-carbohydrate or highly processed food diets lacking in wholegrains and legumes. Older adults — absorption declines with age. People under chronic stress — stress increases the body's demand for B vitamins including thiamine.
Where to get it from food
The best dietary sources of vitamin B1 are wholegrains (especially oats and brown rice), legumes (lentils, black beans, edamame), pork, sunflower seeds, and nutritional yeast. Fortified breakfast cereals are also a reliable source for most people. Unlike fat-soluble vitamins, thiamine isn't stored in large amounts in the body — you need a steady daily supply.
- Real biological mechanism — B1 is directly involved in brain energy metabolism and neurotransmitter production needed for sleep
- Linked to abnormal sleep duration in large population data
- RCT evidence for improved sleep quality scores with supplementation
- Safe, cheap, and available in food — low risk of doing harm
- Especially useful for people with known risk factors for deficiency
- Evidence base is smaller than for magnesium or melatonin — fewer RCTs specifically on sleep
- Most people eating a balanced diet already get enough — supplements may add little benefit if you're not deficient
- The 2022 Korean study shows correlation, not causation — long sleep may reflect poor health rather than low B1 specifically
- The 2025 RCT combined B1 and B2 — hard to isolate how much of the benefit came from B1 alone
Vitamin B1 is not a miracle sleep supplement — but it's a nutrient worth knowing about. If you sleep too much and still feel tired, drink alcohol regularly, or eat a restrictive diet, checking your B1 intake is a reasonable first step. For most people, the answer is food rather than supplements: more wholegrains, lentils, and seeds. If you have clear risk factors for deficiency, a basic B-complex supplement is a low-cost, low-risk option worth trying for a few weeks.
- Lee D. et al. (2022). The Relationship Between Thiamine Intake and Long Sleep Duration: Results From the Korea National Health and Nutrition Examination Survey. Journal of Preventive Medicine and Public Health, 55(6), 520–528. DOI: 10.3961/jpmph.22.313. View on PMC →
- Tao Y. et al. (2025). Impact of Vitamin B1 and Vitamin B2 Supplementation on Anxiety, Stress, and Sleep Quality: A Randomized, Double-Blind, Placebo-Controlled Trial. Nutrients, 17(11), 1821. DOI: 10.3390/nu17111821. View on PMC →