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Vitamin B1 deficiency symptoms

All to know about thiamine (vitamin B1) deficiency

Being deficient in thiamine (vitamin B1) can cause subtle and often overlooked symptoms. Here are eight signs of thiamine deficiency, plus treatments.

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Thiamine (vitamin B1): Deficiency symptoms and treatment
Last updated on November 1, 2023, and last reviewed by an expert on February 12, 2023.

Thiamine, also known as vitamin B1, is one of the eight essential B vitamins.

Thiamine (vitamin B1): Deficiency symptoms and treatment

It plays a key role in several important health functions, and not getting enough of it can lead to thiamine deficiency. This deficiency is known as beriberi if it’s severe and chronic.

This article examines the functions of thiamine, the signs and symptoms of deficiency, and how to ensure you’re getting enough of this essential nutrient in your diet.

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What is thiamine (vitamin B1)?

Thiamine is a vitamin your body needs for growth, development, cellular function, and converting food into energy.

Like the other B vitamins, thiamine is water-soluble. That means it dissolves in water and isn’t stored in your body, so you must consume it regularly. In fact, your body can only store around 20 days’ worth of thiamine at any given time.

Fortunately, thiamine is naturally found in various foods and added to others via fortification. It’s also commonly added to multivitamins or taken as a supplement or part of a vitamin B complex.

Some of the best places to find thiamine in your diet include foods like:

Not getting enough thiamine can lead to thiamine deficiency, which can happen in as little as 3 weeks and affect your heart, nervous, and immune systems. True thiamine deficiency is rare among healthy individuals with adequate access to thiamine-rich foods.

In highly industrialized countries, most people who experience true thiamine deficiency are experiencing other health conditions or procedures.

Symptoms of thiamine (vitamin B1) deficiency

Signs and symptoms of thiamine deficiency can be easy to overlook, as they can be nonspecific and vague, sometimes mimicking symptoms of other conditions.

Below are some of the most common symptoms of thiamine deficiency.

1. Loss of appetite

Experiencing an atypical loss of appetite can be one of the earliest symptoms of thiamine deficiency. Losing your appetite (not feeling hungry) can lead to unintentional weight loss, which can be problematic or unsafe.

One theory behind this is that thiamine may play a key role in regulating hunger and fullness cues in the brain. Inadequate thiamine stores may disrupt how well this process works, making you feel full even when you may not be.

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As a result, you may eat less than you usually would due to a lack of appetite. This could cause you to miss out on vital nutrients potentially.

Animal studies have demonstrated this relationship. For instance, one study found that rats ate significantly less food after receiving a diet deficient in thiamine for 16 days. Their food intake dropped by almost 75% by day 22.

Furthermore, they increased appetite and returned to usual food intake once thiamine was added to their diet.

2. Fatigue

Being deficient in thiamine can show up as fatigue (tiredness), which may come on quickly or over time, depending on the severity of the deficiency. Some sources suggest fatigue can occur within just a few weeks of deficiency.

This symptom makes sense, given the role of thiamine in converting food into energy. Not having enough thiamine in the body means it cannot produce as much energy as fuel.

While fatigue is a widespread symptom that can indicate several other health conditions, many studies have linked it to thiamine deficiency.

In fact, some researchers suggest that fatigue should be prioritized when identifying early signs of thiamine deficiency among people at risk.

3. Irritability

A thiamine deficiency may cause changes in your mood, such as making you more irritable or easily upset.

Feeling irritable is often among the earliest signs of thiamine deficiency, and it may present alongside fatigue within just a few weeks.

Babies with thiamine deficiency frequently express increased irritability as a symptom.

4. Nerve damage

Among the most well-known side effects of prolonged, severe thiamine deficiency (beriberi) is nerve damage, also known as neuropathy.

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In fact, neuropathy from thiamine deficiency was among the first deficiency syndrome identified in humans.

Two types of beriberi can occur: wet beriberi and dry beriberi.

Wet beriberi includes heart failure, whereas dry beriberi occurs without heart failure. Wet beriberi is considered an emergency and can lead to death within a few days if not treated.

Potential symptoms of beriberi can include:

5. Tingling arms and legs

Even though tingling — the sensation of prickliness and “pins and needles” in your arms and legs, also called paresthesia — can be a symptom of severe beriberi, it can also be an earlier symptom of thiamine deficiency. It generally comes before more widespread, brain-related symptoms.

This symptom is because thiamine is required for the expected function of the nerves that reach your arms and legs. When there’s not enough thiamine present, paresthesia can result.

Over time, untreated thiamine deficiency can lead to more serious damage to these peripheral nerves.

6. Blurry vision

Because of thiamine’s role in maintaining healthy nerves, a deficiency can affect the optic nerve in your eyes.

Specifically, this can cause optic nerve swelling, leading to blurred vision. Left untreated, optic nerve damage can eventually result in vision loss.

Still, this is quite rare.

Some small studies have found that supplementation used to correct thiamine deficiency may also significantly improve vision.

In an animal study, researchers found that a thiamine compound effectively prevented alcohol-induced optical nerve damage.

However, the human studies are “case reports,” meaning they followed a single individual. Plus, the results of animal studies don’t always hold true when applied to human health. That means we can’t apply this research to the general population and need more studies.

7. Nausea and vomiting

Like fatigue and irritability, nausea and vomiting can be nonspecific symptoms of many conditions, including thiamine deficiency.

Suggested read: 9 signs and symptoms of vitamin B6 deficiency

These digestive symptoms are more common among people with a thiamine deficiency–related condition called Wernicke encephalopathy. However, they can be a primary symptom even in mild cases of thiamine deficiency, so it’s important to take them seriously.

8. Delirium

Thiamine deficiency can lead to delirium, a serious condition in which you experience:

Severe thiamine deficiency can lead to the development of Wernicke-Korsakoff syndrome (WKS), which involves brain damage and has symptoms of:

WKS is often associated with the overuse of alcohol.

Summary: Symptoms of thiamine deficiency can be vague and hard to diagnose. They may include loss of appetite, fatigue (tiredness), irritability, nerve damage, tingling in your arms and legs, blurry vision, nausea and vomiting, and delirium.

Treatment for thiamine deficiency

Ideally, prevention is the best approach to thiamine deficiency.

Eating a diet rich in thiamine-containing foods can help maintain adequate thiamine stores. Again, deficiencies are rare in communities living in highly industrialized countries with consistent access to food.

Most adults should aim to get 1.1–1.2 mg of thiamine daily.

Eating a diet rich in thiamine-containing foods can help maintain adequate thiamine stores.

Some common sources of dietary thiamine include the following:

Additionally, a thiamine-containing supplement, such as a multivitamin or vitamin B complex, will generally provide most of the recommended daily needs for thiamine per serving. Check the supplement facts panel to see how much is in yours if you take one.

There is no established upper limit for thiamine. That’s because we don’t have evidence suggesting that taking it in high doses poses negative health risks.

Dose supplementation may be used under medical supervision for severe cases of diagnosed thiamine deficiency. For example, thiamine supplementation may be given orally, via injections, or IV in a clinical setting.

Some heart-related symptoms can be reversed within hours to days using this type of clinical thiamine deficiency correction.

It may take 3 to 6 months to reverse brain and nervous system effects, and people with severe neuropathy due to a delay in diagnosis or treatment may have permanent damage.

Testing for a thiamine deficiency

Thiamine deficiency is diagnosed using a physical exam, looking for issues like behavioral or mobility changes and laboratory testing to confirm.

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Urine tests are unreliable for measuring thiamine levels, nor are direct blood tests of thiamine levels.

Instead, medical professionals often use a blood test to measure the activity of the enzyme transketolase. Transketolase activity requires thiamine, so if its activity is reduced in the body, it’s assumed to be due to a lack of thiamine.

Summary: The best approach is to prevent thiamine deficiency in the first place by eating a variety of thiamine-containing foods and potentially using a thiamine-containing supplement. If thiamine deficiency is diagnosed using a reliable lab test, high-dose supplementation is used to correct it.

What causes thiamine deficiency?

The risk of developing thiamine deficiency is generally low in industrialized countries where people have more reliable access to thiamine-containing foods. However, there is a higher risk among certain groups of people.

Some of the most common risk factors for thiamine deficiency include:

Pregnant and breastfeeding or chestfeeding people and individuals with an overactive thyroid may also have a higher risk for thiamine deficiency due to their increased needs for the nutrient.

Additionally, infants exclusively breastfed by thiamine-deficient parents are at higher risk of deficiency.

Summary: Thiamine deficiency is rare in highly industrialized countries with access to thiamine-rich foods and supplements. However, common risk factors for thiamine deficiency include conditions like eating disorders, weight loss surgery, alcohol dependence, and using medications that promote fluid loss.


Although thiamine deficiency is generally uncommon in populations with access to thiamine-rich foods and supplements, factors like certain medications, alcohol dependence, eating disorders, and weight loss surgery can increase your risk of developing it.

There are several symptoms of thiamine deficiency, many of which are subtle and nonspecific, like fatigue and irritability. That vagueness can make the condition difficult to identify and diagnose in many cases.

Symptoms can worsen with a more severe, chronic deficiency, including nerve damage, heart problems, and even paralysis.

The best approach is to eat a variety of thiamine-containing foods or take a multivitamin to prevent a deficiency from occurring.

If thiamine deficiency is diagnosed, many of its effects can be reversed with supplementation. In severe cases, high-dose supplementation is used under medical supervision.

Try this today: Consider the sources of thiamine in your diet and where you could add more. Do you eat beans, lentils, or enriched grains and bread? Or, if you take a multivitamin, check the supplement facts panel to ensure it provides at least your recommended daily needs of thiamine.

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