Vitamin B1, also called thiamine, is a water-soluble nutrient your body uses to convert food into energy. It plays a central role in metabolism and is especially important for your brain and nervous system, which demand enormous amounts of energy to function. Adults need about 1.1 to 1.2 mg per day, and because your body can’t store much of it, you need a steady supply from food.
What Thiamine Does in Your Body
Once you consume thiamine, an enzyme in your blood converts it into its active form, called TPP. This activated version works as a helper molecule for several critical steps in your metabolism. It assists the enzyme complexes that keep your body’s main energy-production cycle running, the process that turns the calories in food into usable fuel for your cells.
Specifically, thiamine helps convert pyruvate (a product of breaking down carbohydrates) into a form that can enter the energy cycle in your mitochondria. Without enough thiamine, this conversion stalls. Lactic acid builds up instead, and your cells, particularly neurons, can’t produce the energy they need. Your brain is especially vulnerable because neurons are among the most energy-hungry cells in the body, relying almost entirely on mitochondrial energy production to fire signals and maintain themselves.
Best Food Sources
Thiamine is found in a wide range of foods, and most people in developed countries get enough through a normal diet. The richest sources per serving include:
- Fortified breakfast cereals: 1.2 mg per serving (100% of the daily value)
- Enriched egg noodles: 0.5 mg per cup, cooked
- Pork chop (bone-in, broiled): 0.4 mg per 3 ounces
- Trout (cooked): 0.4 mg per 3 ounces
- Black beans (boiled): 0.4 mg per half cup
Pork is one of the best natural sources, and legumes, fish, and whole grains round out the list. Many breads, pastas, and cereals in the U.S. are enriched with thiamine, which is why outright deficiency is relatively uncommon in the general population. Still, certain groups face higher risk.
Who Is at Risk for Deficiency
Chronic alcohol use is the most well-known risk factor. Alcohol interferes with thiamine absorption in the gut and increases how much your kidneys excrete. But several other conditions can deplete thiamine levels or block absorption:
- Gastric bypass surgery, which physically alters the digestive tract and reduces nutrient absorption
- Severe morning sickness (hyperemesis gravidarum), which limits food intake during pregnancy
- Chronic diuretic use, which increases thiamine loss through urine
- Dialysis (renal replacement therapy), which filters thiamine out of the blood
- Malabsorption disorders and chronic diarrhea
- Refeeding syndrome, when someone who has been malnourished begins eating again and the body’s sudden demand for thiamine outstrips supply
Pregnancy, breastfeeding, and hyperthyroidism also raise your body’s thiamine requirements, potentially tipping someone with a marginal diet into deficiency.
What Deficiency Looks Like
Because thiamine is water-soluble and your body stores very little of it, deficiency can develop faster than you might expect. The classic deficiency disease is called beriberi, and it comes in two forms depending on which organ system is hit hardest.
Dry beriberi targets the nervous system. It causes peripheral nerve damage, leading to tingling, numbness, and weakness in the legs and feet. Over time, muscle wasting can develop. The nerve damage stems from disrupted signaling in the brain’s chemical messenger systems, essentially starving neurons of energy and poisoning them with byproducts that accumulate when thiamine-dependent enzymes can’t do their job.
Wet beriberi affects the heart and circulatory system. It triggers widespread blood vessel dilation, which forces the heart to pump harder to maintain blood pressure. This can progress to a rapid heart rate, swelling in the lower legs, fluid in the lungs, and eventually heart failure. The “wet” name comes from the visible fluid retention.
Wernicke-Korsakoff Syndrome
The most severe neurological consequence of thiamine deficiency is a two-stage brain disorder seen most often in people with chronic alcohol use. The first stage, Wernicke encephalopathy, classically involves three symptoms: confusion, difficulty walking, and abnormal eye movements. In practice, only a fraction of patients show all three signs, which makes it easy to miss. Up to 90% of cases lack the full triad at diagnosis.
If Wernicke encephalopathy goes untreated, about 80% of survivors progress to Korsakoff syndrome, a condition defined by severe, often permanent memory loss. People with Korsakoff syndrome may be unable to form new memories or recall recent events, while older memories remain relatively intact. This progression is preventable with early thiamine replacement, which is why recognizing the warning signs matters so much.
Supplement Forms and Absorption
Standard thiamine supplements come in water-soluble forms. Because thiamine can’t pass freely through cell membranes, your intestines rely on specific transporter proteins to absorb it. This creates a bottleneck: there’s a limit to how much your gut can take in at once, no matter how large the dose.
Benfotiamine is a synthetic derivative designed to get around that bottleneck. Once swallowed, intestinal enzymes convert it into a fat-friendly form that can slip through the gut lining without needing transporters. The result is plasma thiamine levels roughly five times higher than an equivalent dose of regular thiamine. Despite often being called “fat-soluble,” benfotiamine itself doesn’t actually dissolve in fats. It’s the intermediate compound created during digestion that crosses membranes more easily.
For most people eating a balanced diet, supplementation isn’t necessary. But for those with absorption issues or higher metabolic demands, the difference in bioavailability between standard thiamine and benfotiamine can be meaningful.
Safety
Thiamine has no established upper intake limit. Because it dissolves in water, excess amounts are excreted through urine rather than building up in tissues. This makes toxicity from oral supplements extremely rare. High doses taken by mouth are generally well tolerated, though there’s little evidence that mega-dosing provides benefits for people who aren’t deficient.