Thiamin Deficiency and Beriberi: Causes, Symptoms, and High-Risk Groups

Thiamin, also called vitamin B1, is a water-soluble nutrient the body cannot make on its own, so it must come from food or supplements every day. When intake falls too low for too long, a condition called beriberi can develop, affecting the nervous system, the heart, or both.

What Thiamin Does in the Body

According to the NIH Office of Dietary Supplements (ODS), thiamin works primarily as thiamin diphosphate (TDP), an active form that serves as an essential cofactor for five enzymes involved in glucose, amino acid, and lipid metabolism. In practical terms, this means thiamin plays a critical role in converting the nutrients you eat into usable energy. It also supports the growth, development, and normal function of cells throughout the body.

The evidence that TDP is essential for these metabolic pathways is rated strong by the NIH ODS, meaning it is well established by consistent research.

How Much Thiamin Do Adults Need?

The NIH ODS reports the following Recommended Dietary Allowances (RDAs) for adults aged 19 to 50:

• Men: 1.2 mg per day
• Women: 1.1 mg per day

No Tolerable Upper Intake Level has been set for thiamin because no adverse effects have been reported from high intakes of 50 mg per day or more from food or supplements. The body readily excretes excess thiamin in urine, making toxicity unlikely. That said, always talk to a clinician or pharmacist before choosing a dose for yourself, as individual needs can vary.

How Common Is Thiamin Deficiency?

Most people in the United States consume recommended amounts of thiamin. A national dietary survey cited by the NIH ODS found that only about 6 percent of the population had usual intakes below the Estimated Average Requirement. Deficiency is therefore uncommon in the general population but remains a real concern for specific groups described below.

What Is Beriberi?

Beriberi is the classic disease of thiamin deficiency. It has two main forms:

• Dry beriberi affects the nervous system. Symptoms include numbness or tingling in the hands and feet, muscle weakness, difficulty walking, and pain in the limbs.
• Wet beriberi affects the cardiovascular system. It can cause an enlarged heart, rapid heart rate, fluid buildup in the legs, and in severe cases heart failure.

A third presentation, Wernicke-Korsakoff syndrome, is a serious neurological condition most often linked to heavy alcohol use. Wernicke's encephalopathy is the acute phase, marked by confusion, abnormal eye movements, and loss of muscle coordination. Korsakoff syndrome is the chronic phase, characterized by severe memory problems.

The NIH ODS rates the evidence that thiamin deficiency causes beriberi and Wernicke-Korsakoff syndrome, and that supplemental thiamin can correct these conditions, as strong. If you suspect any of these conditions, seek medical care promptly rather than self-treating.

Who Is at Highest Risk?

People with Heavy Alcohol Use

Alcohol interferes with thiamin absorption in the gut, reduces the liver's ability to store it, and increases the body's demand for it. This combination makes heavy alcohol use the leading cause of thiamin deficiency in high-income countries.

People Taking Certain Medications

Two drug interactions deserve particular attention, and the NIH ODS specifically flags both:

• Loop diuretics such as furosemide (Lasix): Research has linked furosemide use to decreases in thiamin concentrations, possibly reaching deficient levels, because of increased urinary thiamin loss. If you take a loop diuretic regularly, ask your doctor or pharmacist whether your thiamin status should be monitored.
• Fluorouracil (5-fluorouracil, Adrucil) chemotherapy: Several cases of beriberi and Wernicke's encephalopathy have been reported in patients receiving this treatment. The drug may increase thiamin metabolism and block formation of TDP, the active form. Thiamin supplements might reverse some of these effects, but any decision about supplementation during chemotherapy must involve the treating oncologist.

Do not combine thiamin supplements with any medication without first speaking to your doctor or pharmacist.

People with Malabsorption Conditions

Conditions that impair nutrient absorption, including Crohn's disease, bariatric surgery, and chronic diarrhea, can reduce how much thiamin the body takes in even when dietary intake looks adequate on paper.

Older Adults

Reduced food intake, lower absorption efficiency, and a higher likelihood of taking multiple medications all increase the risk of low thiamin status in older adults.

People with Diabetes

Some research suggests that people with diabetes may clear thiamin from the bloodstream more quickly than others. The NIH ODS notes that thiamin or benfotiamine supplements have been studied for improving glucose control or diabetic neuropathy in people with diabetes, but rates this evidence as limited, meaning results are promising but not yet conclusive. A clinician should guide any supplementation decisions in this context.

Other Areas of Research

Researchers have also examined thiamin supplementation in heart failure and cognitive decline. The NIH ODS rates the evidence that thiamin supplementation benefits people with heart failure as limited. Evidence that thiamin supplements improve cognition or treat Alzheimer's disease is rated insufficient, meaning current data do not support a conclusion either way. Research continues in both areas.

Getting Enough Thiamin from Food

Good dietary sources include whole grains, fortified cereals and breads, legumes, nuts, and lean pork. Because thiamin is water-soluble, it can leach into cooking water, so steaming or microwaving vegetables preserves more than boiling.

A Note on Supplements

Thiamin supplements are widely available and are generally considered safe at the doses found in standard multivitamins and B-complex products. However, supplements are not intended to diagnose, treat, cure, or prevent any disease, and these statements have not been evaluated by the FDA. If you are considering a thiamin supplement, especially at doses above the RDA, or if you are taking any prescription medication, speak with a clinician or pharmacist first to determine whether supplementation is appropriate for your situation.

When to See a Doctor

Symptoms such as persistent numbness or tingling in the limbs, unexplained muscle weakness, confusion, or swelling in the legs should always be evaluated by a healthcare provider. These can have many causes, and a clinician can order appropriate tests, including blood thiamin levels, to determine whether deficiency is a factor.