Thiamine, also known as vitamin B1, is one of eight essential B vitamins that has many important functions throughout the body.

It’s used by nearly all your cells and responsible for helping convert food into energy (1).

Since the human body is unable to produce thiamine, it must be consumed through various thiamine-rich foods, such as meat, nuts and whole grains.

Thiamine deficiency is fairly uncommon in developed countries. However, various factors may increase your risk, including (2):

  • Alcohol dependence
  • Old age
  • HIV/AIDS
  • Diabetes
  • Bariatric surgery
  • Dialysis
  • High-dose diuretic use

Many people don’t realize that they have a deficiency, as many of the symptoms are subtle and often overlooked.

Here are 11 signs and symptoms of thiamine deficiency.

Thiamine Deficiency Symptoms

One common early symptom of thiamine deficiency is a loss of appetite, or anorexia.

Scientists believe that thiamine plays an important role in the regulation of satiety.

It helps control the “satiety center” located in the hypothalamus of the brain.

When deficiency occurs, normal action of the “satiety center” is altered, causing the body to feel satiated or full, even when it may not be. This can result in a lack of appetite (3).

One study in rats fed a thiamine-deficient diet for 16 days found that they ate significantly less food. After 22 days, the rats displayed a 69–74% decrease in food intake (3).

Another study in rats fed a thiamine-deficient diet also showed a significant decrease in food intake (4).

In both studies, food intake rapidly increased to baseline after re-supplementation of thiamine.

Summary Thiamine plays an important role in the control of the “satiety center.” One common symptom of thiamine deficiency is a loss of appetite.

Fatigue may occur gradually or suddenly. It can range from a slight decrease in energy to extreme exhaustion, likely depending on the severity of deficiency.

Since fatigue is such a vague symptom with numerous possible causes, it can be commonly overlooked as a sign of thiamine deficiency.

However, considering the vital role thiamine plays in converting food into fuel, it’s no surprise that fatigue and lack of energy is a common symptom of deficiency.

In fact, many studies and cases have linked fatigue to thiamine deficiency (5, 6, 7, 8).

Summary Although a vague symptom, fatigue is a common sign of thiamine deficiency and should not be disregarded.

Irritability is the feeling of agitation and frustration. When you are irritable, you often become upset quickly.

Irritability can be caused by various physical, psychological and medical conditions.

An irritable mood is noted to be one of the first symptoms of thiamine deficiency. It may occur within days or weeks of deficiency (9).

Irritability has been especially documented in cases involving infants with beriberi, a disease caused by thiamine deficiency (10, 11, 12).

Summary Frequent irritability may be an early sign of thiamine deficiency, especially in infants.

Thiamine deficiency can affect the motor nerves.

If left untreated, the damage to your nervous system caused by thiamine deficiency could cause changes in your reflexes.

Reduced or absent reflexes of the knee, ankle and triceps are often observed, and as deficiency progresses, it may affect your coordination and ability to walk (13).

This symptom has often been documented in undiagnosed thiamine deficiency in children (12).

Summary The damage caused by untreated thiamine deficiency can affect your motor nerves and cause a reduction in or loss of reflexes.

Abnormal tingling, prickling, burning or the sensation of “pins and needles” in the upper and lower limbs is a symptom known as paresthesia.

The peripheral nerves that reach your arms and legs rely heavily on the action of thiamine. In cases of deficiency, peripheral nerve damage and paresthesia can occur.

In fact, patients have experienced paresthesia in the beginning phases of thiamine deficiency (14, 15, 16).

Also, studies in rats have shown that thiamine deficiency has led to peripheral nerve damage (17, 18).

Summary Thiamine contributes to the health of the nerves in many ways. A deficiency may cause paresthesia.

Generalized muscle weakness is not uncommon, and its cause is often difficult to determine.

Short-term, temporary muscle weakness happens to almost everyone at some point. However, persistent, long-standing muscle weakness without a clear cause or reason may be a sign of thiamine deficiency.

In multiple cases, patients with thiamine deficiency have experienced muscle weakness (16, 19, 20).

Furthermore, in these cases, muscle weakness greatly improved after thiamine re-supplementation.

Summary Muscle weakness, specifically in the upper arms and legs, may occur in thiamine deficiency.

Thiamine deficiency may be one of the many causes of blurry vision.

Severe thiamine deficiency can cause swelling of the optic nerve, inducing optic neuropathy. This can result in blurry, or even loss of, vision.

Multiple documented cases have linked blurry vision and vision loss to severe thiamine deficiency.

Furthermore, patients’ vision improved significantly after supplementation with thiamine (21, 22, 23, 24).

Summary Thiamine deficiency can cause damage to the optic nerve, which may result in blurry or loss of vision.

Although gastrointestinal symptoms are less common in thiamine deficiency, they can still occur.

It’s not exactly understood why digestive symptoms may manifest with thiamine deficiency, but documented cases of gastrointestinal symptoms have been resolved after thiamine supplementation (25).

Vomiting may be more common in infants with deficiency, as it was found to be a common symptom in infants who consumed a thiamine-deficient, soy-based formula (10).

Summary On rare occasions, gastrointestinal symptoms like nausea, vomiting or abdominal pain may be symptoms of thiamine deficiency.

Your heart rate is a measure of how many times your heart beats per minute.

Interestingly, it can be affected by your thiamine levels. Not enough thiamine could result in a slower than normal heartbeat.

Marked decreases in heart rate have been documented in studies involving thiamine-deficient rats (26, 27).

An abnormally slow heart rate as result of thiamine deficiency may cause increased fatigue, dizziness and a greater risk of fainting.

Summary A thiamine deficiency may cause a decrease in heart rate, resulting in increased fatigue and dizziness.

Given that thiamine deficiency can affect heart function, shortness of breath may occur, especially with exertion.

This is because thiamine deficiency can sometimes lead to heart failure, which occurs when the heart becomes less efficient at pumping blood. This can ultimately result in fluid accumulation in the lungs, making it difficult to breathe (28).

It is important to note that shortness of breath can have many causes, so this symptom alone is not usually a sign of thiamine deficiency.

Summary Heart failure caused by thiamine deficiency can cause breathlessness. This can occur when fluid accumulates in the lungs.

Multiple studies have linked thiamine deficiency and delirium.

Delirium is a serious condition that results in confusion, reduced awareness and the inability to think clearly.

In severe cases, thiamine deficiency can cause Wernicke-Korsakoff syndrome, which involves two types of closely related brain damage (1, 29, 30).

It’s symptoms often include delirium, memory loss, confusion and hallucinations.

Wernicke-Korsakoff syndrome is often associated with thiamine deficiency caused by alcohol abuse. However, thiamine deficiency is also common in elderly patients and may contribute to the occurrence of delirium (31).

Summary Some people with thiamine deficiency may show signs of delirium and develop Wernicke-Korsakoff syndrome, especially if thiamine deficiency is a result of chronic alcoholism.

Eating a healthy, balanced diet that includes thiamine-rich foods can help prevent a thiamine deficiency.

The recommended daily intake (RDI) is 1.2 mg for men and 1.1 mg for women (1).

Below is a list of good sources of thiamine, as well as the RDI found in 100 grams (32):

  • Beef liver: 13% of the RDI
  • Black beans, cooked: 16% of the RDI
  • Lentils, cooked: 15% of the RDI
  • Macadamia nuts, raw: 80% of the RDI
  • Edamame, cooked: 13% of the RDI
  • Pork loin, cooked: 37% of the RDI
  • Asparagus: 10% of the RDI
  • Fortified breakfast cereal: 100% of the RDI

Many foods contain small amounts of thiamin, including fish, meat, nuts and seeds. Most people are able to meet their thiamine requirement without supplementation.

Additionally, in many countries, cereals, breads and grains are often fortified with thiamin.

Summary Thiamine is found in a variety of whole foods, such as fortified breakfast cereals, macadamia nuts, pork, beans and lentils. The recommended daily intake for thiamine is 1.2 mg for men and 1.1 mg for women.

Although thiamine deficiency is fairly uncommon in developed countries, various factors or conditions, such as alcoholism or advanced age, can increase your risk.

Thiamine deficiency can present itself in various ways, and symptoms are often nonspecific, which makes it difficult to identify.

Fortunately, a thiamine deficiency is usually easy to reverse with supplementation.