Uses, Benefits, Side Effects, Dosage, Precautions

Thiamine, or vitamin B1, is a water-soluble vitamin that is found in some foods and may also be taken as a supplement. The body’s cells need thiamine in order to generate energy, develop, grow, and function. Thiamine plays a role in metabolizing glucose (sugar), which is part of the process used by the body to provide cells with energy.

For healthy adults in the United States, a balanced diet usually provides enough thiamine. Thiamine is stored in the liver, but only in small amounts, so people need a steady supply from their diet or a supplement to avoid a deficiency.

People who live with certain conditions, including alcohol use disorder, diabetes, certain gastrointestinal conditions or surgeries, or heart failure, may need to watch for thiamine deficiencies.

This article discusses the potential uses of thiamine. It also covers risk factors of a thiamine deficiency and the potential side effects of taking supplements.

Uses of Thiamine

Thiamine is important in maintaining overall good health. A deficiency of thiamine, or vitamin B1, may go undiagnosed and is associated with poor health outcomes, including death. The body uses thiamine to get the energy to grow cells and support body functions. 

Thiamine helps some of the enzymes in the body that are used in the metabolism of glucose. This makes thiamine levels important in diseases of the metabolic and gastrointestinal systems.

For that reason, a deficiency may lead to a lack of certain enzymes. A severe deficiency could lead to decreased production of some enzymes and go on to cause problems in brain function.

Supplement use should be individualized and vetted by a healthcare professional, such as a registered dietitian, pharmacist, or healthcare provider. No supplement is intended to treat, cure, or prevent disease.

Wernicke-Korsakoff Syndrome

Alcohol use disorder could lead to a lack of thiamine and the development of Wernicke-Korsakoff syndrome. This syndrome is a late stage of thiamine deficiency. The treatment includes supplementing with thiamine, but it may not cure it.

Two randomized double-blind placebo-controlled trials (those in which neither the researchers nor participants know whether they received the active ingredient) compared oral thiamine and injections of thiamine for Wernicke-Korsakoff syndrome. These studies were not successful in determining what the dosage of thiamine should be to reverse the symptoms of this condition or to prevent it.

When symptoms of this condition (confusion and problems with balance and walking) appear in people with alcohol use disorder, supplementation with thiamine through an IV is recommended.

Diabetes

People with diabetes may be at risk of a thiamine deficiency. The body needs thiamine to keep blood glucose levels steady, so this can lead to complications in people with diabetes. Thiamine may also help in preventing the cardiovascular complications associated with diabetes.

For people with diabetes who start to develop kidney damage (nephropathy), thiamine supplementation might be recommended.

Some of the studies on diabetes and thiamine have been observational, which means that they are taking information from what people are doing and what their thiamine levels are but not using any kind of intervention. For that reason, there still needs to be more studies on when and how to use thiamine in people with diabetes.

Heart Failure

People with heart failure (the heart does not pump enough blood to fulfill the body’s needs) have been shown to have lower levels of thiamine. Being older, having other health conditions, and not being able to get enough vitamins and minerals through the diet may contribute to this problem.

One meta-analysis showed that many studies are not using the same types of measurements to understand how low thiamine levels contribute to heart failure. For that reason, it’s difficult to know how much of a role low levels play in contributing to heart failure.

Some older small, randomized double-blind placebo-controlled trials showed that thiamine supplements improved one aspect of heart function in people with heart failure. Other newer studies found this was not the case after thiamine therapy. Yet it isn’t clear that thiamine helps heart failure patients do any better in the long term.

Not enough is known about how thiamine supplements may help people with heart failure, and the authors of one meta-analysis are calling for more research.

Alzheimer’s Disease

Whether supplementing with thiamine in people with Alzheimer’s disease (a progressive condition causing problems with memory, thinking, and behavior) may be beneficial is still being studied.

A placebo-controlled trial in people with Alzheimer’s disease showed that supplementing with a form of thiamine was considered safe. The authors used several tools to measure the cognitive (thinking and memory) levels of the people in the trial over time. They then compared those who received the thiamine and those who didn’t.

The study found that mental decline was less in those who received thiamine. The study was small, and the authors have called for a larger trial, but they are encouraged that thiamine supplementation might be beneficial in Alzheimer’s disease.

Thiamine Deficiency

A thiamine deficiency may occur when people are either not getting enough thiamine from their diet or they are not absorbing it properly. People who aren’t able to eat enough food with thiamine in it, such as those who are receiving nutritional support because of an illness, may not be getting enough of this vitamin.

What Causes a Thiamine Deficiency?

Thiamine is absorbed in the small intestine. Deficiencies are historically not common in developed areas of the world because most people get enough thiamine from food. However, bariatric surgery (weight-loss surgery that modifies the digestive system) rates increased dramatically from 2006 through 2021, and it is a risk factor for thiamine deficiency.

Incidence of a thiamine deficiency is higher in some groups of people, including:

• People with alcohol use disorder
• People with human immunodeficiency virus (HIV)/AIDS
• People with diabetes
• People who have had bariatric surgery

A healthcare provider may recommend getting thiamine levels tested for some people, especially before and after bariatric surgery. This may help in catching a deficiency early and getting the support to bring levels up to normal and avoid complications.

How Do I Know If I Have a Thiamine Deficiency?

When thiamine levels get too low, it may initially cause signs and symptoms such as:

• Cardiovascular problems (such as an enlarged heart)
• Confusion
• Lack of appetite
• Muscle weakness
• Short-term memory loss or other mental problems
• Weight loss 

A more severe or long-term thiamine deficiency may cause complications, including conditions called beriberi and Wernicke-Korsakoff syndrome.

Groups With a Higher Incidence of Thiamine Deficiency

Thiamine deficiencies are more common in areas of the world where there is less access to food sources of thiamine. In the developed world, a lack of thiamine is more often caused by a disease or condition that is either causing an inability to consume foods with enough thiamine or one that interferes with thiamine absorption.

Factors that can increase incidence include:

• Age: Because people tend to have more health problems and take various medications as they get older, vitamin deficiencies may be more common, including thiamine deficiency.
• Alcohol use disorder: Drinks that contain ethanol prevent thiamine absorption. People with alcohol use disorder may also have other vitamin and mineral deficiencies.
• Bariatric surgery: Surgery for weight loss may lead to problems with vitamins and minerals being absorbed well. This can include thiamine, which is why checking thiamine levels may be part of the pre- and postsurgical process for weight loss surgeries.
• Diabetes: People with type 1 and type 2 diabetes may have low levels of thiamine. The reasons are not entirely clear, but one theory is that thiamine is not being absorbed well because it is being processed too quickly by the kidneys.
• HIV/AIDS: The complications of HIV/AIDS may lead to several different vitamin and mineral deficiencies, including thiamine.

Beriberi

Beriberi is a condition caused by low levels of thiamine. It is more common in developing parts of the world than it is in developed areas. This is because people in developing areas may not get enough thiamine in their diet.

Beriberi causes problems with the cardiovascular and central nervous systems, which broadly means it can affect the heart and the muscles. It is a progressive condition. In rare cases, when it is not treated, it could lead to irreversible damage to the brain.

The signs and symptoms of beriberi can include:

• Confusion
• Chest pain
• Fatigue
• Fever
• Loss of muscle tissue
• Nausea or vomiting
• Numbness or tingling in the fingers or feet (paresthesia)
• Rapid heartbeat (tachycardia)
• Weakness

Beriberi is also associated with gastric surgery, which could be done for weight loss or for treating a condition such as cancer. As many as 30{7b6cc35713332e03d34197859d8d439e4802eb556451407ffda280a51e3c41ac} of people who have surgery on the upper digestive tract have some level of thiamine deficiency. Other health problems, such as diabetes, may worsen the condition.

When beriberi is diagnosed—and even when it is strongly suspected—thiamine supplementation is the treatment. Thiamine is given first by IV for several days and then with an oral supplement, along with several other B vitamins.

Guidelines from the American Society for Metabolic and Bariatric Surgery also recommend that thiamine levels be tested in people who have gastric surgery and are at risk for a thiamine deficiency.

Wernicke-Korsakoff Syndrome

Wernicke-Korsakoff syndrome is a common outcome of thiamine deficiency in the United States than beriberi. It is especially found in people who have alcohol use disorder. It is also associated with HIV/AIDS, drug dependency, digestive diseases, and certain types of blood cancer.

This syndrome is serious and can even be deadly. Treatment is with thiamine supplementation. Other vitamins and supplements may also be used as a treatment because other deficiencies might also be present. 

However, some cases of this syndrome become so severe that people develop chronic (long-term) health problems, especially with memory. These people will also need more intensive therapy to improve their ability to learn and retain memories.

The signs and symptoms of Wernicke-Korsakoff syndrome can include the following:

What Are the Side Effects of Thiamine?

Thiamine doesn’t stay in the body for long, which is one reason deficiencies occur. It’s not thought that supplementing with thiamine causes any adverse side effects. 

When thiamine is given through an IV for serious deficiencies, there may be a risk of an allergic reaction, but the benefits would outweigh the risks in these cases. Giving the supplement slowly and with fluids may help cut this risk, but there aren’t any accepted guidelines.

Dosage: How Much Thiamine Should I Take?

The recommended daily allowance (RDA) of thiamine can vary by age and pregnancy status as follows, in milligrams (mg), which can be obtained through food sources or oral supplements:

• Birth to 6 months: 0.2 mg
• 7–12 months: 0.3 mg
• 1–3 years: 0.5 mg
• 4–8 years: 0.6 mg
• 9–13 years: 0.9 mg
• 14–18 years: Males 1.2 mg; females 1.0 mg
• 19–50 years: Males 1.2 mg; females 1.1 mg
• 51 years and over: Males 1.2 mg; females 1.1 mg
• During pregnancy: 1.4 mg
• While lactating: 1.4 mg

Note that Verywell Health prefers to use inclusive terminology, but when citing health authorities or studies, the terms relating to sex and gender from those sources are used.

What Happens If I Take Too Much Thiamine?

There’s no upper limit set on thiamine supplements. Taken orally, it’s not expected to cause adverse reactions at higher levels, but there’s also no data to prove otherwise. However, as with any supplement, it’s still important to check with a healthcare provider on an appropriate dosage.

Interactions

Oral thiamine isn’t expected to interact with other medications. However, there is some evidence that the drugs Lasix (furosemide) and Adrucil (fluorouracil) could cause the body to lose too much thiamine. Healthcare providers may recommend a supplement to people taking those drugs.

It is essential to read the ingredient list and nutrition facts panel of a supplement carefully to know which ingredients and how much of each ingredient is included. Please review this supplement label with your healthcare provider to discuss any potential interactions with foods, other supplements, and medications.

How to Store Thiamine

Oral thiamine should be kept away from sunlight in a cool, dry place. It should be discarded after the expiration date on the packaging has passed.

Similar Supplements

Thiamine is vitamin B1, of which there are several different types that are used as supplements. Some occur naturally in foods but might also be made synthetically in a lab.

Some other forms of thiamine or vitamin B1, or derivatives, include:

• Allithiamine (thiamine allyl disulfide or TAD)
• Benfotiamine (S-benzoylthiamine-O-monophosphate)
• Fursultiamine (thiamine tetrahydrofurfuryl disulfide or TTFD), sold under the brand names Alinamin-F, Benlipoid, Bevitol Lipophil, Judolor, and Lipothiamine
• Prosultiamine (thiamine propyl disulfide or TPD), including the brand Jubedel
• Sulbutiamine, sold under the brands Arcalion and Enerion

Sources of Thiamine & What to Look For

Most people get enough thiamine in their food. It is naturally present in whole grains, meat (especially pork), and fish. Some foods (bread, cereals, and infant formula) are fortified with thiamine to ensure most people receive enough in their diet.

Food Sources of Thiamine

There are many whole-food and fortified-food sources of thiamine, including:

• Long grain white rice
• Breakfast cereals, fortified
• Egg noodles, fortified
• Pork chops
• Trout
• Black beans
• English muffins, fortified
• Mussels
• Tuna
• Macaroni
• Acorn squash

Thiamine Supplements

Thiamine (vitamin B1) is often found in multivitamins, usually with other B vitamins. It can also be taken as a supplement on its own, in capsule or liquid form. 

Often, supplements that can be bought over the counter contain thiamine mononitrate or thiamine hydrochloride, which are stable forms of thiamine. Some available supplements may include one or more synthetic forms of vitamin B1.

Thiamine will be given in the hospital through an IV for severe deficiencies.

Summary

Thiamine is a vitamin that is important to essential functions in the body. It is also not stored by the body, so a steady supply is needed. Most people get enough thiamine through their diet. However, certain groups of people may have a deficiency, either because they can’t get enough thiamine in their diet or their bodies can’t absorb it properly.

A thiamine deficiency can become serious, so it’s important for those who might lack it to be tested and receive a supplement.