A 47-year-old woman struggling with an eating disorder for a long time was hospitalized with Wernicke encephalopathy and beriberi, diseases causing abnormal eye movements, visual impairment, confusion, and improper limb movement and heart function.

Two conditions—beriberi and Wernicke-Korsakoff syndrome—are closely linked to vitamin B1 deficiency. Cataracts may also be related to a lack of this vitamin.

You might be surprised to learn that thiamine could be behind your ability to climb six flights of stairs without breaking a sweat, stay in a good mood, or avoid cataracts well into your 70s. The following are the main benefits thiamine offers.

1. Improves Nervous System and Brain Function

Thiamine, as well as other B-complex vitamins, are essential for proper nervous system and brain function.

Vitamin B1 plays a critical role in producing myelin sheath, the protective outer sheath of nerve fibers. Myelin is vital to the transmission of rapid nerve impulses from the central nervous system to the periphery and vice-versa. Thiamine deficiency can result in neuropathy, potentially leading to conditions such as seizures and epilepsy.

Along with the syndrome itself, thiamine deficiency can cause dementia in Wernicke-Korsakoff syndrome, prompting researchers to hypothesize that thiamine supplementation might benefit Alzheimer’s disease patients. Furthermore, reduced glucose metabolism is consistently observed in Alzheimer’s and is considered a key biomarker of disease progression. Thiamine-dependent processes, which are vital for glucose metabolism, are also reduced in the brains of Alzheimer’s disease patients. Studies using oral thiamine have demonstrated improvement in cognitive function among these patients.

One 2013 pilot study discovered that high doses of thiamine were linked to a significant improvement in fatigue-related symptoms in multiple sclerosis.

2. Prevents Heart Disease, Such as Heart Failure

One primary function of vitamin B1 is maintaining proper levels of acetylcholine. Acetylcholine deficiency can affect cardiac function since the nervous system uses this neurotransmitter to communicate with the heart. Consequently, symptoms such as chest pain, high blood pressure, or congestive heart failure may arise.

An adequate thiamine level can also prevent blood pyruvate and blood lactate levels from rising. This function is important because if these levels become excessively high, they can contribute to muscle discomfort and affect cardiac tissue, potentially leading to an increased heart rate and blood pressure.

Thiamine is especially vital in managing heart failure since its deficiency can impair heart function and mimic heart failure symptoms. Malnutrition is common among heart failure patients and is linked to disease severity and morality.

In a 2013 meta-analysis, thiamine supplementation showed a notable improvement in net change in the cardiac function of heart failure patients, although additional studies are needed.

3. Reduces Depression

Excessively high levels of acetylcholine can contribute to depression or anxiety, whereas vitamin B1 can help balance levels.

Depression has a tie to insufficient thiamine levels. A 2024 study uncovered a noticeable link between thiamine intake and depression in the general American adult population. However, this relationship only goes up to a certain level of thiamine consumption, which was 1.35 milligrams per day. Beyond this point, how much thiamine people consume doesn’t always match up with the level of depression they feel. Therefore, researchers believe these findings offer valuable insights into potential strategies for depression prevention through adequate thiamine intake.

4. Fights Infectious Diseases

B vitamins are also known as “anti-stress” vitamins due to their potential immune system support and stress resilience enhancement. They also possess antiviral properties and help shield immune cells from oxidative stress damage.

One 2021 study involving 166 critically ill COVID-19 patients who had been admitted to intensive-care units discovered a noticeable connection between the use of thiamine for treatment and lower mortality risks. It also showed a reduced occurrence of blood clotting.

Sepsis is a serious reaction to an infection. Having low levels of vitamin B1 can be dangerous in such cases. A 2018 retrospective study involving 369 septic patients showed that administering thiamine intravenously was associated with improvements in mortality rate.

In a 2001 review of three case studies, patients with chronic hepatitis B experienced reduced severity of their hepatitis symptoms after consuming 100 milligrams of vitamin B1 daily.

5. Converts Food Into Energy

Thiamine plays a crucial role in converting carbohydrates into energy by serving as a cofactor for enzymes that break down glucose, the main energy source for cells. In addition, our bodies also require thiamine to produce adenosine triphosphate (ATP), a universal energy source in the body.

6. Protects Against Cataracts

Thiamine and other essential nutrients such as protein, vitamin A, and other B-group vitamins may reduce the likelihood of cataract formation.

In one 2022 study, researchers analyzed data from Korean adults aged 60 years and above collected through the Korean National Health and Nutrition Examination Survey. They found that men who consumed more vitamin B1 had a reduced risk of developing cataracts.

7. Combats Diabetes and Obesity

A lack of thiamine seems to disrupt the pancreas’ usual insulin production and worsen high blood sugar levels. In a 2013 study, 12 hyperglycemic individuals were given 300-milligram thiamine supplements daily for six weeks. Unlike the placebo group, the group taking thiamine experienced an improvement in fasting blood sugar, insulin, or insulin resistance. The researchers concluded that high-dose thiamine supplements might help prevent the worsening of fasting blood sugar and insulin levels and enhance glucose tolerance.

Thiamine deficiency is prevalent among people with higher body mass indexes (BMI), although the specific mechanisms remain unidentified. In a 2011 study, receiving 150 milligrams of thiamine daily for one month led to notable reductions in glucose levels.

8. Lowers Cholesterol

Thiamine protects against the thickening of arterial smooth muscle cells involved in worsening the narrowing of the arteries in arteriosclerosis. It correlates negatively with triglyceride and low-density lipoprotein (LDL) levels (“bad” cholesterol) and positively with high-density lipoprotein (HDL) levels (“good” cholesterol). One study involving Type 2 diabetes patients found thiamine increased HDL after supplementing for three months, but the authors noted that more well-designed, randomized controlled trials are needed to confirm the vitamin’s potential to raise HDL. In healthy older individuals, higher plasma thiamine levels are connected to lower total cholesterol concentrations, potentially delaying vascular inflammation and atherosclerosis.

9. Staves Off Inflammatory Diseases

Thiamine has been found to influence the immune system by lessening inflammation and oxidative stress, which can harm immune cells and contribute to the onset of different illnesses, such as infections, rheumatoid arthritis, inflammatory bowel disease (IBD), and asthma.

In a 2016 study using rats with rheumatoid arthritis, thiamine reduced joint inflammation, paw edema, and pain sensitivity. A decrease in the production of certain inflammatory substances accompanied this.

Although the National Institutes of Health reports that thiamine deficiency is rare or confined to specific populations in the United States, as most Americans are supposed to obtain sufficient thiamine through their diets, extensive research indicates that thiamine deficiency is often overlooked or under-recognized.

The recommended daily allowance (RDA) for thiamine is around 1.1 to 1.2 milligrams for adults. Despite this, measurable thiamine deficiency has been found in various patient groups, with incidence rates varying from 20 percent to over 90 percent, depending on the study. For instance, even obese individuals have been found to have a high prevalence of thiamine deficiency, ranging from 15 percent to 29 percent. This indicates that the RDA may not be adequate for modern lifestyles.

Primary thiamine deficiency refers to a condition in which there is inadequate intake or absorption of thiamine from dietary sources. Thiamine deficiency can occur within two to three months of insufficient intake.

Secondary thiamine deficiency is when thiamine levels become depleted due to factors other than inadequate dietary intake, including chronic stress, pregnancy, diarrhea, some medications, and certain diseases.

Symptoms of vitamin B1 deficiency include:

• Fatigue
• Muscle pain and weakness
• Anxiety
• High blood pressure
• Painful peripheral neuropathies: Pain in the hands, feet, and calves with increased sensitivity, reduced feeling, and problems with movement.
• Brain fog
• Weight loss and loss of appetite
• Depression
• Reduced immunity
• Irritability
• Chest and abdominal discomfort
• Increased heart rate

Thiamine deficiency can trigger seizures in people who are already prone to having them but haven’t shown clear signs of seizures yet. Additionally, it can cause conditions such as beriberi and Wernicke-Korsakoff syndrome.

Beriberi (Wet and Dry)

Thiamine deficiency leads to markedly impaired carbohydrate digestion. This interferes with energy generation, increases harmful free radicals, and decreases neurotransmitters, leading to beriberi.

Dry beriberi primarily manifests as a neurological condition affecting the peripheral nervous system. It’s characterized by symptoms such as peripheral neuropathy, general discomfort, muscle weakness, seizures, or heightened reflexes in tendons. One 32-year-old woman was diagnosed with dry beriberi after a month of poor eating habits, nausea, vomiting, painful urination, and significant weight loss. She later developed such neuropathies; two days after starting thiamine, she could get up out of bed and walk with a walker. Her symptoms continued to improve, but a month later, she still occasionally had pain in her lower extremities and had to use a walker.

Wet beriberi is distinguished by cardiovascular symptoms, including increased heart rate, heart enlargement, edema, breathing difficulties, and, ultimately, congestive heart failure.

Wernicke-Korsakoff Syndrome

This syndrome is more common in the United States than beriberi. It combines both Wernicke’s encephalopathy and Korsakoff’s psychosis.

Korsakoff’s psychosis leads to confusion, dysphonia (difficulty producing vocal sounds), memory impairment, and confabulation (unintentional creation of false or fabricated memories). Confabulation can be a prominent feature, with patients unintentionally creating false memories or false answers to questions they are asked. It is often done without hesitation. Korsakoff’s psychosis often develops after repeated Wernicke’s encephalopathy episodes due to chronic thiamine deficiency. It is not always reversible after thiamine replenishment.

Chronic alcoholism increases the prevalence of this disorder by approximately eight to 10 times. Of note, it is important that alcoholics always receive thiamine before any intravenous glucose solutions. Otherwise, the glucose infusion can overwhelm the meager thiamine reserve and cause irreversible Korsakoff’s psychosis.

Before diving into how to boost your thiamine intake, it’s helpful to understand the different types of thiamine. Thiamine can be obtained from both natural and synthetic sources.

Natural Sources

• Thiamine (vitamin B1): This is one of the naturally occurring forms of thiamine found in different foods.
• Thiamine pyrophosphate (TPP): Also known as thiamine diphosphate (TDP), TPP is the biologically active form of thiamine. It plays a crucial role in energy metabolism, including the breakdown of glucose, lipids, and proteins. It is also found in food.
• Allithiamine: This is a naturally occurring disulfide derivative of thiamine found in various Allium plant species. It is formed enzymatically when the garlic bulb is cut or crushed. Allithiamine possesses potent antioxidant and anti-inflammatory properties. Its synthetic form is called thiamine tetrahydrofurfuryl disulfide (TTFD).

Synthetic Sources

• Thiamine mononitrate (TMN): A synthetic thiamine salt, which is a stable form of thiamine, it is commonly used in supplements and fortified foods. It is converted into TPP in the body.
• Thiamine hydrochloride (THCl): This is another synthetic thiamine salt used in supplements and food fortification. Like TMN, it is converted into TPP in the body but has a notably slower degradation rate.
• Benfotiamine: A synthetic precursor of thiamine with enhanced lipid solubility and higher tissue penetration and bioavailability, it allows for better absorption in the body to prevent thiamine deficiency. Research suggests that benfotiamine has antioxidant and anti-inflammatory properties.

The best sources of vitamin B1 are foods, especially whole foods that naturally contain it.

The main dietary sources of thiamine are as follows, with thiamine content per 100 grams:

• Yeast extract spread (23.4 milligrams)
• Crude rice bran (2.75 milligrams)
• Flax seeds (1.64 milligrams)
• Dried sunflower seeds (1.48 milligrams)
• Hulled hemp seeds (1.28 milligrams)
• Tahini (1.22 milligrams)
• Black beans (0.9 milligram)
• Soybeans (0.874 milligram)
• Pistachios (0.87 milligram)
• Whole dried sesame seeds (0.791 milligram)
• Quaker organic instant oatmeal (0.73 milligram)
• Pork (0.697 milligram)
• Pecans (0.66 milligram)
• Rice bran bread (0.653 milligram)
• Peanuts (0.64 milligram)
• Brazil nuts (0.617 milligram)
• Red kidney beans (0.608 milligram)
• Buckwheat (0.539 milligram)
• Ham (0.468 milligram)

A word of caution: A 2024 study found that some breakfast cereals and oat-based foods contain a chemical compound called chlormequat, which may reduce fertility and potentially harm the developing fetus at lower doses than the recommended daily intake amounts. Chlormequat is banned in U.S. agriculture; however, since 2018, imported contaminated crops have been permitted.

Approximately 55 percent of the thiamine in the American diet is derived from foods naturally rich in thiamine, while the other 45 percent is obtained from foods supplemented with it. Thiamine-fortified foods sometimes provide four times the RDA. However, despite consuming abundant foods fortified with thiamine, thiamine deficiency remains prevalent among Americans.

Our cultural perception often relegates thiamine-related diseases to the past or underdeveloped nations, leading us to overlook them as potential health threats. Moreover, the assumption that nutrient fortification adequately meets our thiamine needs is increasingly challenged.

Even if you consume foods rich in thiamine, you might not absorb enough of it due to factors such as how you cook your food, your diet, your medications, and even your mood. So how can you maximize thiamine absorption? Follow these tips:

• Avoid high-heat cooking: Thiamine is sensitive to high heat and prolonged cooking and leaches into water, resulting in its loss during cooking or soaking.
• Eat less ultra-processed food, carbs, and sugar: Eating too many carbs and sugar can reduce the thiamine in the body and inhibit its absorption. Since thiamine can also be removed during food processing, to compensate for these losses, thiamine is often enriched or added back to processed foods.
• Avoid drinking too much coffee, tea, and alcohol: Compounds found in coffee and tea, such as tannins and anti-thiamine factors, can hinder thiamine absorption in the gastrointestinal tract or reduce the amount of thiamine in the body. Increased thiamine loss in urine can occur due to factors such as alcohol misuse. Alcohol can interfere with the absorption and metabolism of thiamine and increase the body’s demand for it.
• Keep a calm mind: Exposure to any type of stress leads to higher energy usage and an increase in the body’s metabolic rate. As thiamine is essential for energy production, the increased metabolic activity during stress can increase the body’s demand for thiamine and reduce thiamine levels more rapidly.
• Be mindful of certain medications and treatments: Diuretics increase urine production and can lead to greater excretion of thiamine and other water-soluble vitamins in the urine. Long-term treatment with seizure medications can lower the levels of B vitamins, including vitamin B1, by interfering with thiamine absorption. In addition, stomach bypass surgery changes the digestive tract’s structure and reduces the stomach’s size, which can reduce the absorption of nutrients such as thiamine. In later sections, you'll find other drugs that could interact with vitamin B1.

Approximately 20 percent to 30 percent of older adults show lab indicators of potential thiamine deficiency, attributed to factors such as inadequate dietary intake, chronic disease, use of multiple medications, and reduced thiamine absorption due to aging.

If you have certain conditions, they can change thiamine requirements. These are a few examples:

• Conditions that increase thiamine requirements: hyperthyroidism (excess thyroid hormone), pregnancy, breastfeeding, intense physical activity, and fever.
• Conditions that obstruct thiamine absorption: prolonged diarrhea, gluten-induced gastrointestinal damage, celiac disease, and Crohn’s disease.
• Disorders that hinder thiamine metabolism: liver and kidney diseases and metabolic disorders. Certain genetic defects have been identified that impair thiamine transport and metabolism, namely defects in SLC19A2, SLC19A3, SLC25A19, and the TPK1 gene.
• Conditions that increase thiamine loss: diabetes. Decreased thiamine levels could result from increased thiamine clearance by the kidneys in these patients.

Eating disorders can also result in low thiamine intake.

Combining thiamine and vitamin C can help lower the risk of oxalate nephropathy (kidney disease)Fju, lessen oxidative damage and cell death, and restore organ function. In addition, it may reduce organ harm during severe illness, with vitamin C acting as a powerful antioxidant in the bloodstream and thiamine helping generate nicotinamide adenine dinucleotide phosphate (NADPH), which further boosts cellular antioxidant capacity.

Additionally, thiamine relies on magnesium for absorption in the gastrointestinal tract, activation into its active form—thiamine diphosphate—and the optimal functioning of thiamine-dependent enzymes within cells.

Most people do not need thiamine supplements, as food alone is enough. For those who do, supplements are available in various forms, such as tablets, soft gels, and lozenges. In severe deficiency cases, thiamine can be given intravenously.

There are also different types of thiamine supplements, including:

• Multivitamins: Multivitamins containing vitamin B1 can come in the form of children’s chewable tablets and liquid drops. They usually provide at least 1.2 milligrams of thiamine.
• B-complex vitamins: This product contains all eight vitamin Bs, usually providing 1.5 milligrams of thiamine or more. Since consuming a single B vitamin over time can lead to an imbalance in vitamin B group intake, many experts advise using B-complex vitamins.
• (Natural) thiamine: Some over-the-counter thiamine supplements and multivitamins contain natural thiamine extracted from guava, holy basil, and lemon.
• Thiamine hydrochloride (THCl): Synthetic thiamine salts—TMN and THCI—are the most commonly used forms of thiamine supplements. They are both stable and water-soluble. However, they are considered less healthy than the supplements made with naturally occurring thiamine, as they are derived from coal tar, hydrochloric acid, or acetonitrile with ammonia. Nutritionist Judith DeCava believes THCl is harmful since it can initially alleviate fatigue, but over time, it may lead to increased fatigue due to the accumulation of pyruvic acid.
• Thiamine mononitrate (TMN): Although TMN is commonly used, some consider it unhealthy because it’s synthetically produced from the same sources as TCIHCI.
• Benfotiamine: Benfotiamine is a synthetic form of thiamine that has been chemically modified. This modification makes benfotiamine more fat-soluble compared to regular thiamine. As a result, benfotiamine can penetrate cell membranes more easily and is more readily absorbed by the body, leading to higher thiamine levels in tissues and cells. Although it’s synthetic, benfotiamine is generally considered safe and has many health benefits.
• Thiamine tetrahydrofurfuryl disulfide (TTFD): TTFD supplements have been used extensively to maintain health and treat diseases, and they’re generally considered safe for long-term supplementation.

Intravenous (IV) administration and certain bacteria can also synthesize thiamine.

The gut microbiota, a diverse collection of microorganisms inhabiting the human gastrointestinal tract, also serves as a significant source of vitamins, including thiamine. For instance, after we ingest soy, when it undergoes fermentation with certain bacteria, the bacteria help produce more thiamine.

Consuming a diverse range of healthy foods with different types of fibers and nutrients, probiotic-rich foods, and prebiotic foods can support gut microbiome health.

The existing recommended dietary reference intakes (DRIs) for thiamine in the United States were established in 1998 by the Food and Nutrition Board (FNB) within the Institute of Medicine at the National Academies.

According to the European Food Information Council (EUFIC), healthy adults consuming an average 2,000-calorie diet should consume 1 milligram of thiamine daily.

There are controversies regarding thiamine’s optimal dosage for treatment. Some studies suggest that higher doses of up to 1,500 milligrams may be beneficial in treating certain conditions, including diabetes, heart failure, and hypermetabolic states. Another 2022 study found no evident advantage of using high doses of thiamine compared to intermediate or lower doses in treating Wernicke-Korsakoff syndrome, thus supporting the patient-specific treatment approach instead.

Cardiac issues in wet beriberi typically improve within 24 hours of treatment initiation, and symptoms of dry beriberi may also improve. However, in cases where the deficiency progresses to Korsakoff syndrome, initial treatment may lead to minimal improvement, and some symptoms may persist permanently.

The symptoms of mild to moderate thiamine deficiency are often disregarded or misdiagnosed.

The diagnosis of thiamine deficiency is based on understanding the patient’s medical history, physical examination, and lab test results. Currently, there is no lab test to confirm the diagnosis. Several lab tests are used instead, including:

• Blood tests: Although blood tests lack accuracy in diagnosing thiamine deficiency, as they do not reflect the actual thiamine levels within cells, doctors still often conduct them to check electrolyte levels to rule out other potential causes of symptoms.
• Erythrocyte transketolase test: The level of erythrocyte transketolase activity indicates disruptions in thiamine metabolism. The erythrocyte transketolase test can evaluate thiamine levels by measuring transketolase activity before and after adding TPP. More than a 25 percent increase in activity may reflect an abnormal result. However, this test’s specific normal range values have not yet been defined.
• High-performance liquid chromatography (HPLC): HPLC is a technique used in analytical chemistry to separate, identify, and quantify components of a mixture, such as a blood sample. A more advanced analytical method is liquid chromatography with tandem mass spectrometry. It is also the most commonly used technique to measure thiamine phosphorylated esters in the patient’s serum or blood sample.
• Echocardiogram: An echocardiogram uses ultrasound to produce images of the heart. It assesses heart function and helps identify reasons behind cardiac symptoms. For instance, it can detect whether or not thiamine deficiency is behind heart failure.
• Radiographic studies: Radiographic studies refer to diagnostic imaging techniques that use radiation to create detailed images of the internal body. As Wernicke’s encephalopathy involves symmetric changes in the thalamus and many other parts of the brain, imaging tests can detect these abnormalities.

Thiamine deficiency is usually diagnosed by a favorable response to thiamine treatment in a patient suspected of having the condition. Thiamine treatment typically does not improve similar conditions that involve damage or dysfunction of multiple peripheral nerves caused by other conditions.

Diagnosing cardiovascular beriberi may pose challenges when other conditions leading to heart failure are also present. A trial of thiamine therapy may be beneficial in such cases.

Thiamine toxicity is unlikely to occur from food sources alone, as the body regulates absorption and eliminates excess through urine. Therefore, no established toxic level exists for it, and high intakes (50 milligrams or more per day) have not been associated with adverse effects, leading to the absence of established upper limits (ULs) by the FNB.

However, excess thiamine intake may have side effects, including stomach upset, flushing, hives, itchiness, weakness, sweating, nausea, and restlessness. In rare instances, thiamine can trigger a severe allergic reaction, with symptoms such as difficulty breathing, sudden confusion, and dizziness.

In addition, long-term consumption of any single B vitamin can lead to an imbalance of other essential B vitamins. Therefore, if you want to take a vitamin B supplement, opting for a B-complex vitamin that contains all of the B vitamins may be advisable.

The medicines that may interact with thiamine include the following:

• Diuretics lead to a greater excretion of thiamine in the urine.
• Digoxin, a medication for heart conditions, might hinder heart cells’ absorption and utilization of thiamine, especially when combined with furosemide, a loop diuretic.
• Phenytoin: Certain individuals (not all) on phenytoin, a drug for epilepsy and seizures, may experience reduced thiamine levels in their blood after prolonged use, potentially affecting the drug’s side effects.
• 5-Fluorouracil is a chemotherapy drug used to treat different cancers. It blocks the process of turning thiamine into its active form, TPP, resulting in lower thiamine levels.
• Erythromycin belongs to a class of antibiotics called macrolides, used for various bacterial infections. It has been linked to reduced thiamine levels in patients, likely because it hinders thiamine transport.
• Patiromer is commonly used to manage high potassium levels in the blood. It can bind to some orally administered drugs, including thiamine, in the gastrointestinal tract, thus preventing their absorption.
• Oral contraceptives affect the body’s thiamine metabolism, potentially leading to deficiency.
• Metformin, commonly used to manage Type 2 diabetes, can contribute to thiamine deficiency, as it can inhibit a type of thiamine transporter in the body.