Vitamin B1, known as thiamine, is a water-soluble vitamin that your body needs to convert food into usable energy, build DNA components, and keep your nervous system functioning. Unlike fat-soluble vitamins that can be stored for months, thiamine reserves in the body are small and deplete within a few weeks of inadequate intake. That makes it a nutrient you need to replenish regularly, and its absence can cause surprisingly severe damage, particularly to the brain and heart.
What Thiamine Actually Does Inside Your Cells
Thiamine itself is not the workhorse. Once it enters your cells, an enzyme converts it into its active form, thiamine pyrophosphate (TPP). TPP then acts as a helper molecule for several enzymes that sit at critical junctures in your metabolism. Three of these enzymes operate inside mitochondria, handling the breakdown of pyruvate (a product of sugar metabolism), alpha-ketoglutarate (a key step in the energy cycle), and branched-chain amino acids (building blocks from protein).1American Journal of Human Genetics. Thiamine Pyrophosphokinase Deficiency in Encephalopathic Children with Defects in the Pyruvate Oxidation Pathway A fourth enzyme, transketolase, works in a different pathway that generates the raw materials for DNA and RNA synthesis as well as molecules your cells use to manage oxidative stress.2PubMed. Transketolase: observations in alcohol-related brain damage research
The practical upshot is that without enough thiamine, your cells cannot efficiently extract energy from carbohydrates. The brain, which runs almost exclusively on glucose and has no meaningful energy reserves of its own, is hit first and hardest. The heart, another organ with relentless energy demands, is a close second. This explains why thiamine deficiency syndromes overwhelmingly target the nervous system and the cardiovascular system.
Where You Get Thiamine and How Much You Need
Thiamine is found in a wide range of foods, though usually in modest amounts. Whole grains, pork, legumes, nuts, and seeds are among the richest natural sources. Many countries also fortify staple grains like white rice and wheat flour with thiamine, which has dramatically reduced deficiency rates in populations that rely on refined grains. Cooking does degrade thiamine to some extent because it is sensitive to heat and water, so boiling vegetables in large amounts of water and then discarding the liquid washes away a meaningful fraction.
The European Food Safety Authority ties the recommended intake to how many calories you eat, setting the population reference intake at roughly 0.4 mg per 1,000 kilocalories for all age groups from infancy onward, including during pregnancy and lactation.3PubMed Central. Dietary reference values for thiamin In the United States, the recommended daily amount for adults works out to about 1.1 mg for women and 1.2 mg for men. Most people eating a varied diet in a country with grain fortification meet these targets without trying. The trouble starts when diets are severely restricted, when absorption is impaired, or when the body’s demand for thiamine outstrips the supply.
Beriberi and the Two Faces of Deficiency
Severe thiamine deficiency causes beriberi, a disease that was historically devastating in parts of Asia where polished white rice was the dietary staple. Beriberi comes in two main forms, categorized by which organ system bears the brunt.
“Dry” beriberi targets the peripheral nerves. The severity tracks with how deficient someone is and for how long. Early symptoms include tingling, burning, or numbness in the feet and hands, progressing to muscle weakness, difficulty walking, and loss of reflexes. The underlying damage involves the axons of nerve cells, and severe cases can mimic other neurological conditions like Guillain-Barré syndrome.4PubMed Central. Dry Beriberi Due to Thiamine Deficiency Associated with Peripheral Neuropathy and Wernicke’s Encephalopathy Mimicking Guillain-Barré syndrome
“Wet” beriberi affects the heart. It produces high-output heart failure, where the heart pumps hard but inefficiently, along with fluid buildup and lactic acidosis. The condition is rarely seen in wealthy countries today, but case reports still surface in individuals with extremely poor diets or severe social isolation.5PubMed Central. Wet Beriberi Associated with Hikikomori Syndrome In a clinical setting, the distinction between dry and wet beriberi is not always clean. Some patients show features of both.
Wernicke-Korsakoff Syndrome and the Brain
The most feared neurological consequence of thiamine deficiency is Wernicke’s encephalopathy, an acute brain emergency characterized by confusion, difficulty coordinating movement, and eye-movement abnormalities. If untreated, it can progress to Korsakoff syndrome, a chronic condition marked by severe memory impairment. Patients with Korsakoff syndrome often cannot form new memories and may confabulate, inventing plausible-sounding stories to fill gaps in recall without realizing they are doing so.6PubMed Central. Thiamine Deficiency and Brain Injury: Neuroanatomical Changes in the Wernicke-Korsakoff Syndrome
Chronic alcohol misuse remains the classic risk factor. Alcohol interferes with thiamine absorption in the gut, reduces the liver’s ability to store it, and impairs the enzyme that converts thiamine to its active form. Heavy drinkers also tend to eat poorly, compounding the problem. Several alcohol-related neuropsychiatric syndromes beyond Wernicke-Korsakoff have been linked to thiamine deficiency, including alcoholic cerebellar degeneration and alcoholic peripheral neuropathy.7PubMed Central. High-dose thiamine strategy in Wernicke-Korsakoff syndrome and related thiamine deficiency conditions associated with alcohol use disorder
But alcohol is not the only cause. Wernicke’s encephalopathy is increasingly documented in people with severe vomiting during pregnancy, after weight-loss surgery, in patients with chronic gastrointestinal disease, and in those with cancer.6PubMed Central. Thiamine Deficiency and Brain Injury: Neuroanatomical Changes in the Wernicke-Korsakoff Syndrome Any condition that sharply reduces food intake or impairs nutrient absorption for weeks at a stretch can tip someone into deficiency.
Bariatric Surgery and Unexpected Deficiency
Weight-loss surgeries, particularly procedures that bypass sections of the small intestine, create a lasting risk for thiamine deficiency. The intestinal rearrangement reduces the surface area available for absorbing nutrients, and the dramatic drop in food intake during the early post-operative period compounds the problem. Thiamine, vitamin B12, and copper are the most frequently depleted micronutrients after bariatric surgery.8PubMed. Neurological Complications of Bariatric Surgery
Neurological complications can appear surprisingly early. One reported case involved a 23-year-old woman who developed double vision and a cranial nerve palsy just two months after a Roux-en-Y gastric bypass, a presentation traced to acute thiamine deficiency.9PubMed Central. Thiamine Deficiency After Bariatric Surgery: Early Neurological Complications and Nutritional Monitoring Most bariatric surgery programs now prescribe lifelong multivitamin supplementation and periodic blood work to catch deficiencies before they cause damage. If you have had or are planning this type of surgery, staying on top of your supplementation schedule matters a great deal.
Infantile Beriberi in Low-Resource Settings
In parts of Southeast Asia and other regions where white rice dominates the diet and fortification programs are limited, breastfed infants remain vulnerable to thiamine deficiency. Infants depend entirely on their mother’s milk for thiamine. If the mother’s diet is deficient, the breast milk will be too. The typical presentation involves infants around two to three months of age who develop heart failure rapidly.10PLoS Neglected Tropical Diseases. Clinically Unapparent Infantile Thiamin Deficiency in Vientiane, Laos A study in Laos documented 43 breastfed infants admitted with beriberi, all showing signs of heart failure or shock in the absence of infection, who improved rapidly after receiving thiamine injections.11PubMed. Dietary and socio-economic factors associated with beriberi in breastfed Lao infants
The dramatic response to treatment is one of beriberi’s defining features: a critically ill infant can begin recovering within hours of an injection. The flip side is that without treatment, infantile beriberi can be fatal. This makes it one of those conditions where simple, inexpensive interventions save lives, provided someone recognizes what is happening. In many low-resource settings, cases go undiagnosed because the symptoms overlap with sepsis and other common causes of infant illness.
Diabetes and Thiamine Depletion
One of the more striking findings in thiamine research involves people with diabetes. A study comparing plasma thiamine levels in diabetic patients and healthy volunteers found that thiamine was reduced by about 75% in both type 1 and type 2 diabetes. The mechanism appears to involve the kidneys: renal clearance of thiamine was increased roughly 16-fold in type 2 diabetes and 24-fold in type 1 diabetes, meaning the body was flushing thiamine out at an extraordinary rate.12PubMed Central. High prevalence of low plasma thiamine concentration in diabetes linked to a marker of vascular disease
This does not mean every person with diabetes is clinically thiamine deficient or needs separate supplementation beyond what a normal diet provides. But it does suggest that the standard measures of thiamine status might underestimate the problem in diabetic populations, and that the vascular complications of diabetes could be partly linked to inadequate thiamine levels. Research into whether thiamine or its derivatives could help protect against diabetic nerve damage and blood vessel disease is ongoing, though the clinical evidence is not yet strong enough to support firm recommendations.
Thiamine in Critical Care
Over the past decade, researchers have been exploring whether giving intravenous thiamine to critically ill patients, particularly those in septic shock, improves outcomes. The rationale is straightforward: thiamine deficiency causes lactic acidosis because cells cannot complete the normal energy-extraction pathway, and lactic acidosis is a hallmark of septic shock. If some of that acidosis is driven by unrecognized thiamine deficiency, replacing thiamine should help.13PubMed Central. Thiamine (vitamin B1) in septic shock: a targeted therapy
A large meta-analysis pooling 35 trials and nearly 3,500 patients found that thiamine administration did not significantly reduce mortality overall. It did, however, shorten the duration of shock by about 11 hours on average, modestly lower lactate levels, and improve organ function scores.14PubMed. Effect of intravenous thiamine administration on critically ill patients: A systematic review and meta-analysis of randomized controlled trials A separate meta-analysis focusing specifically on sepsis found a dramatic reduction in the need for kidney dialysis in the thiamine group. In an exploratory subgroup of patients who were actually thiamine-deficient at baseline, a potential mortality benefit emerged, though the sample was small.15Clinics. Efficacy of thiamine (vitamin B1) in sepsis and septic shock: A meta-analysis of randomized controlled trials
The takeaway for now is that blanket thiamine supplementation for everyone in the ICU has not been shown to save lives, but identifying and treating deficient patients early may make a real difference. Since thiamine is cheap and has virtually no toxicity, many intensivists now check levels or simply give it empirically to patients with unexplained lactic acidosis.
Thiamine and Alzheimer’s Disease
Alzheimer’s disease features a well-documented reduction in the activity of thiamine-dependent enzymes in the brain. Autopsy studies of confirmed Alzheimer’s patients consistently show decreased activity of key enzymes including alpha-ketoglutarate dehydrogenase, pyruvate dehydrogenase, and transketolase.16PubMed. Alterations of thiamine phosphorylation and of thiamine-dependent enzymes in Alzheimer’s disease The reductions correlate with the severity of dementia measured before death, and the disruption of thiamine-related metabolic processes can plausibly contribute to the energy failure and neuronal loss seen in the disease.17Antioxidants & Redox Signaling. Thiamine-dependent processes and treatment strategies in neurodegeneration
Some oral thiamine trials have reported improvements in cognitive function in Alzheimer’s patients. However, absorption of thiamine is poor in elderly individuals, which limits how much of the vitamin actually reaches the brain when taken by mouth.18PubMed Central. Role of thiamine in Alzheimer’s disease Whether thiamine or its more absorbable derivatives could meaningfully slow cognitive decline remains an open and active area of research. The existing data are suggestive enough to keep scientists interested but not strong enough to recommend thiamine supplementation as a treatment for Alzheimer’s.
Benfotiamine and Better Absorption
Standard thiamine (as thiamine hydrochloride) has a practical limitation: it is water-soluble and poorly absorbed at higher doses because intestinal transport is saturated. This has driven interest in lipid-soluble thiamine derivatives, the most studied being benfotiamine. Because benfotiamine is fat-soluble, it can cross cell membranes by passive diffusion rather than relying on the limited number of transporter proteins in the gut.
Head-to-head pharmacokinetic studies confirm the difference is substantial. One study found that benfotiamine delivered roughly 11 times more thiamine into the blood compared to the same oral dose of thiamine hydrochloride.19PubMed. Pharmacokinetic study of benfotiamine and the bioavailability assessment compared to thiamine hydrochloride Another study demonstrated superior bioavailability from benfotiamine even when the dose was only 40% as large as the water-soluble comparator, along with greater stimulation of transketolase activity in red blood cells.20Annals of Nutrition and Metabolism. Bioavailability Assessment of the Lipophilic Benfotiamine as Compared to a Water-Soluble Thiamin Derivative
Benfotiamine has been studied in animal models of neurodegeneration and in some human clinical trials, with beneficial effects reported in both settings.21PubMed Central. Neuroprotective Effects of Thiamine and Precursors with Higher Bioavailability: Focus on Benfotiamine and Dibenzoylthiamine It is widely available as a supplement in many countries and is sometimes prescribed in Europe for diabetic neuropathy. For most healthy people eating a normal diet, regular thiamine intake from food is perfectly adequate. Benfotiamine becomes more relevant when someone has increased needs, poor absorption, or a condition where higher tissue levels of thiamine may be therapeutic.
Rare Genetic Conditions Involving Thiamine
A handful of inherited disorders directly affect how the body handles thiamine. The most well-characterized is thiamine-responsive megaloblastic anemia syndrome, also called Rogers syndrome. It is an autosomal recessive condition caused by mutations in the gene encoding one of the two thiamine transporter proteins. People with this syndrome develop a triad of megaloblastic anemia, diabetes, and hearing loss, typically appearing in early childhood.22PubMed Central. Thiamine responsive megaloblastic anemia syndrome associated with patent ductus arteriosus The gene responsible was mapped to the long arm of chromosome 1.23PubMed Central. Localization of the gene for thiamine-responsive megaloblastic anemia syndrome, on the long arm of chromosome 1, by homozygosity mapping
As the name implies, high-dose thiamine treatment can partially reverse the anemia and, in some patients, improve blood sugar control and slow hearing deterioration, though the degree of response varies. Other genetic conditions involve defects in the enzyme that converts thiamine to its active form (thiamine pyrophosphokinase), leading to severe neurological disease in early childhood.1American Journal of Human Genetics. Thiamine Pyrophosphokinase Deficiency in Encephalopathic Children with Defects in the Pyruvate Oxidation Pathway These conditions are rare, but they illustrate how tightly the body’s thiamine machinery is regulated and how quickly things unravel when any piece of it fails.
How Beriberi Was Traced to Diet
The story of how thiamine was discovered is one of the earliest examples of nutritional epidemiology. In the 1880s, a Dutch physician named Christiaan Eijkman was working in the Dutch East Indies (present-day Indonesia) trying to identify the infectious agent behind beriberi, which was then assumed to be caused by a germ. He noticed that chickens fed polished white rice developed leg paralysis resembling beriberi, while chickens fed unpolished brown rice did not.24PubMed. The discovery of thiamin The observation was serendipitous; the chickens had been switched to leftover hospital rice for cost reasons, and the paralysis appeared only after the switch.
It took decades to move from Eijkman’s observation to the isolation of the actual compound. The Polish biochemist Casimir Funk coined the term “vitamine” in 1912 partly based on work with the anti-beriberi factor in rice bran. Thiamine was finally isolated in crystalline form in the 1920s and synthesized in the 1930s. Eijkman shared the 1929 Nobel Prize in Physiology or Medicine for his foundational work. The entire arc, from mysterious disease to nutrient identification, helped establish the concept that specific diseases could be caused not by something present in the environment but by something absent from the diet.