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

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 make sure you’re getting enough of this essential nutrient in your diet.

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Thiamine is a vitamin your body needs for growth, development, and cellular function, as well as converting food into energy (1).

Like the other B vitamins, thiamine is water-soluble. That means that it dissolves in water and isn’t stored in your body, so you need to consume it on a regular basis. In fact, your body can only store around 20 days’ worth of thiamine at any given time (2).

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

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

  • enriched white rice or egg noodles
  • fortified breakfast cereal
  • pork
  • trout
  • black beans
  • sunflower seeds
  • acorn squash
  • yogurt
  • many commercial bread varieties
  • corn

Not getting enough thiamine can lead to thiamine deficiency, which can happen in as little as 3 weeks and affect your heart, nervous system, and immune system. True thiamine deficiency is rare among healthy individuals with adequate access to thiamine-rich foods (2, 3).

In highly industrialized countries, most people who experience true thiamine deficiency are experiencing other health conditions or procedures (2).

Signs and symptoms of thiamine deficiency can be easy to overlook, as they can be nonspecific and vague, sometimes mimicking symptoms of other conditions (4).

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 stores of thiamine may disrupt how well this process works, making you feel full even when you may not actually be (5).

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

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 (5).

Furthermore, an increase in appetite and return to usual food intake returned once thiamine was added back 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 (2).

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

While fatigue is a widespread symptom that can indicate a number of other health conditions, many studies have linked it to thiamine deficiency (6, 7).

In fact, some researchers suggest that fatigue should be prioritized when identifying early signs of thiamine deficiency among people at risk for it (8).

3. Irritability

Having a thiamine deficiency may cause some 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 (2).

Babies with thiamine deficiency frequently express increased irritability as a symptom (9, 10).

4. Nerve damage

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

In fact, neuropathy from thiamine deficiency was among the first deficiency syndrome identified in humans (2).

There are two types of beriberi that 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 (2, 11).

Potential symptoms of beriberi can include (12, 13):

  • tingling limbs
  • loss of sensitivity in feet and fingers
  • muscle weakness
  • rapid heartbeat
  • difficulty waking up
  • mental confusion
  • coordination problems
  • lower body paralysis (inability to move the legs)

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 (14).

The reason behind this symptom is that 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 (15).

Over time, untreated thiamine deficiency can lead to more serious damage to these peripheral nerves (16).

6. Blurry vision

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

Specifically, this can cause swelling of the optic nerve that leads to blurred vision. Left untreated, optic nerve damage can eventually result in vision loss.

Still, this is quite rare (17).

Some small studies have found that supplementation used to correct thiamine deficiency may also significantly improve vision in these instances (18, 19, 20).

In an animal study, researchers found that a thiamine compound was effective for preventing alcohol-induced optical nerve damage (21).

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 we need more studies.

7. Nausea and vomiting

Like fatigue and irritability, nausea and vomiting can be nonspecific symptoms of many conditions, including thiamine 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, 22, 23).

8. Delirium

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

  • confusion
  • reduced awareness of your environment
  • an inability to think clearly

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

  • delirium
  • confusion
  • hallucinations
  • memory loss

WKS is often associated with the overuse of alcohol (24).

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.

Ideally, prevention is the best approach to thiamine deficiency.

Eating a diet rich in thiamine-containing foods can help maintain adequate thiamine stores in the body. 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 per day (25).

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

Some common sources of dietary thiamine include the following:

  • enriched white rice, 1 cup (186 grams) cooked: 0.3 mg
  • enriched egg noodles, 1 cup (160 grams) cooked: 0.5 mg
  • black beans, 1/2 cup (92 grams): 0.2 mg
  • whole wheat bread, 1 slice: 0.1 mg
  • macadamia nuts, 1/2 cup (66 grams): 0.5 mg
  • pork chop, 3 ounces (85 grams) : 0.5 mg
  • yogurt, plain, 1 cup (245 grams): 0.1 mg
  • sunflower seeds, 1/4 cup (35 grams): 0.5 mg
  • lentils, 1 cup (198 grams) cooked: 0.33 mg

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. Just be sure to check the supplement facts panel to see how much is in yours if you choose to take one.

There is no established upper limit for thiamine. That’s because we don’t have any evidence suggesting that taking it in high doses poses negative health risks (25, 26).

For severe cases of diagnosed thiamine deficiency, high dose supplementation may be used under medical supervision. For example, thiamine supplementation may be given orally, via injections, or using an IV in a clinical setting (2, 11).

Using this type of clinical thiamine deficiency correction, some heart-related symptoms can be reversed within hours to days (2).

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 (2).

Testing for a thiamine deficiency

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

Urine tests are not reliable 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. The activity of transketolase requires thiamine, so if its activity is reduced in the body, it’s assumed to be due to a lack of thiamine (11).

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.

The risk for 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 (1, 2, 11, 27):

  • alcohol dependence or long-term misuse
  • older age
  • AIDS
  • long-term use of parenteral nutrition, or a way of receiving nutrients using an IV into the bloodstream
  • chronically elevated blood sugar levels
  • chronic vomiting
  • eating disorders, such as anorexia nervosa or bulimia nervosa
  • weight loss surgery
  • diets high in polished rice or processed grains that lack thiamine
  • dialysis, used to treat kidney conditions
  • high dose use of diuretics (medications used to treat fluid retention)
  • health conditions that affect your ability to absorb vitamins and minerals

Pregnant and breastfeeding or chestfeeding people, as well as individuals with overactive thyroid, may also have a higher risk for thiamine deficiency due to their increased needs for the nutrient (11).

Additionally, infants who are exclusively breastfed by thiamine-deficient parents are at higher risk of deficiency (27).

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 the use of 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, and may include conditions like 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.

Just one thing

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