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Thiamine (Vitamin B1) Deficiency Symptoms, Causes & Treatment

Written by Aleksa Ristic, MS (Pharmacy) | Last updated:
Puya Yazdi
Medically reviewed by
Puya Yazdi, MD | Written by Aleksa Ristic, MS (Pharmacy) | Last updated:
Thiamine deficiency

“Beriberi” may sound cute, but the consequences of this condition can be fatal. Advanced thiamine deficiency causes heart and nerve damage and increases the risk of various diseases. Read on to learn what signals deficiency early on and what you can do to prevent it.

What is Thiamine Deficiency?

Roles of Vitamin B1

Thiamine, also known as vitamin B1, helps you break down food and deliver energy to each cell in your body. In the form of thiamine pyrophosphate (TPP), or thiamine diphosphate (TDP), vitamin B1 supports the enzymes that [1, 2, 3, 4]:

  • Produce energy in your mitochondria
  • Maintain nervous system health and brain function
  • Boost immunity
  • Combat inflammation

Deficiency Criteria

Thiamine deficiency can result from reduced intake, enhanced loss, or impaired metabolism of this essential nutrient.

The term “beriberi” was coined to describe malnourished people with severe thiamine deficiency and distinct symptoms of heart and nerve damage. In developed countries, it’s mostly limited to people with alcoholism and other health disorders, which we’ll discuss later in this post [5, 6].

Normal thiamine blood levels depend on the lab method and literature source. Generally speaking, people with less than 66-70 nmol/L of thiamine diphosphate are potentially deficient [7, 8].

However, blood thiamine has notable limitations as a diagnostic tool. Please see the “Diagnosis” section for more details.

”Beriberi” refers to severe thiamine deficiency with heart and nerve damage, which rarely occurs in developed countries. Blood levels of < 66-70 nmol/L of thiamine diphosphate may indicate a deficiency.

People at Risk

Some vulnerable groups have increased demand for thiamine and are at a higher risk of deficiency; they include:

  • Athletes and active people [9]
  • Alcohol abusers [10, 11]
  • Pregnant and nursing women [12]
  • Diabetics [13]
  • Cancer patients [14]


1) Alcoholism

Chronic alcohol abuse is the most common cause of thiamine deficiency in the United States and other developed countries. Alcoholism depletes thiamine levels by [10, 11, 15]:

  1. Preventing people from eating enough food
  2. Blocking thiamine absorption in the gut
  3. Increasing the body’s demand for thiamine
  4. Inhibiting thiamine storage due to liver damage
  5. Preventing the brain and other organs from using thiamine

A lack of this vitamin can severely damage the nerves, and experts recommend extensive thiamine treatment for all people with a history of alcohol abuse [16].

2) Poor Nutrition & Eating Disorders

Poor Nutrition

Unfortunately, thiamine deficiency is a serious issue for malnourished people in “third world” countries. It’s particularly common in poor Asian regions where polished rice and other processed grains are staples of the diet, and people cannot afford vitamin-rich foods [17, 18].

Bran contains most of the thiamine in rice; thus, milling and the removal of rice bran deplete vitamin B1, making people prone to deficiency if they don’t or can’t eat meat and legumes [5].

Breastfed infants from deficient mothers face similar dangers, often with severe impact on their development. Babies may also suffer from beriberi if they are fed inadequate milk-replacement formulas [19, 20, 21].

Eating Disorders

People with eating disorders such as anorexia lack an array of essential nutrients because they do not eat enough food. They may experience life-threatening nerve damage due to thiamine deficiency [22, 23].

Food intake after prolonged starvation, known as refeeding syndrome, drastically increases thiamine breakdown and may also trigger deficiency symptoms [24, 25].

Thiamine deficiency may occur among poor malnourished people who mainly eat polished rice. Eating disorders such as anorexia and refeeding syndrome also increase the risk.

3) Digestive Disorders

Prolonged diarrhea and vomiting may cause excess vitamin B1 loss. Patients who experience confusion and vision impairment need immediate medical care and the supply of thiamine, fluid, and electrolytes [26, 27].

For the same reason, severe vomiting during pregnancy (hyperemesis gravidarum) may cause thiamine deficiency if left untreated [28].

IBD and other diseases with impaired bowel function can also prevent you from getting enough of this vitamin [29, 30, 31].

4) Gut Surgery

Any surgery performed on the stomach or intestines can reduce thiamine absorption and make you prone to deficiency.

Thiamine deficiency is also a possible side effect of bariatric (weight loss) surgeries, which change the size or structure of the stomach and small intestine. Experts suggest checking thiamine status before the surgery and supplementing in people at risk of deficiency [32, 33, 34, 35].

5) Obesity

Up to 30% of obese people seeking bariatric surgery already have low thiamine levels, which often go undiagnosed [36, 37].

According to a study of 400 patients, higher BMI (body mass index) increases the risk of thiamine deficiency. This may be due to a diet high in refined sugar and fats and low in whole grains [35, 36].

6) Parenteral Nutrition

People who are unable to eat and digest food depend on a steady supply of parenteral (injected) nutrients. Despite decades of experience and advances in parenteral nutrition, some patients still get thiamine deficiency due to low vitamin B1 content in the formulations [38, 39, 40].

Prolonged glucose infusions without added vitamin B1 can also drop thiamine levels and even cause nerve damage [41, 1].

7) Diuretics

People who take diuretics (“water pills”) long-term produce larger amounts of urine, which flushes more thiamine from the body and raises the risk of deficiency.

Patients with heart failure are especially vulnerable, as they receive large doses of furosemide (Lasix) and other potent diuretics [42, 43].

In one clinical trial, high doses of furosemide (80 mg/day) caused severe thiamine deficiency in 98% of patients (24/25). Besides increasing urination, this drug may also directly inhibit thiamine uptake into the cells that need it [44, 45].

8) Diabetes

Vitamin B1 supports several enzymes involved in glucose metabolism. The function of these enzymes is often impaired in people with diabetes [13].

In a study of 94 patients, blood thiamine was 76% lower in type 1 and 75% lower in type 2 diabetic people, compared with healthy volunteers. Both diabetic groups also lost more thiamine in their urine [46].

According to a study of 60 patients, kidney damage may cause thiamine loss in diabetics [47].

Diabetes may cause thiamine deficiency due to impaired enzyme function and increased urinary loss of this vitamin.

9) Genetics

Mutations in the following genes can impair thiamine transport into cells and increase the risk of deficiency [48]:

An error can also occur due to mutations in one or more enzymes that transform thiamine into its active forms, such as thiamine pyrophosphokinase 1 (TPK1) [48].

10) Other

The following conditions can increase the risk of thiamine deficiency:

Magnesium enables the conversion of thiamine into its active form, thiamine pyrophosphate (TPP), and they work together to produce energy. Magnesium deficiency may thus mimic thiamine deficiency and lessen the effects of supplementation [58, 59, 60].

Therefore, if you suspect you are deficient in thiamine, make sure you get enough magnesium in your diet as well.

Signs & Symptoms

1) General Symptoms

Initially, thiamine deficiency can produce general symptoms such as [61, 62]:

  • Fatigue
  • Reduced appetite and weight loss
  • Muscle cramps
  • Irritability
  • Constipation
  • Tongue and mouth inflammation

2) Beriberi

Prolonged deficiency causes typical neurological beriberi symptoms, including [48, 63, 64]:

  • Leg numbness
  • Tingling and burning sensations
  • Visual impairments
  • Loss of memory
  • Confusion

That said, beriberi is rare in the US and other developed countries. It occurs after months of severe deficiency, mostly due to alcohol abuse or health disorders described above [61].

Dry Beriberi

Dry beriberi is a form with dominant nerve damage and neurological symptoms described above. It can sometimes resemble Guillain-Barré syndrome with ascending paralysis (progressing from the legs up), numbness, and low blood pressure [65, 14].

Wet Beriberi

Wet beriberi manifests with heart failure, causing signs and symptoms such as [19, 66]:

  • Increased heart rate
  • Fast breathing
  • Dilated heart muscle
  • Swollen hands and feet

It can cause heart damage typical of certain respiratory conditions like cor pulmonale, in which the right side of the heart is enlarged [66, 67].

Shoshin beriberi is a severe and rapid form of heart failure which often ends in death [5, 19, 64].

Some symptoms, especially the burning and tingling sensations in the feet and legs, can appear in both wet and dry beriberi [61].

Severe thiamine deficiency may lead to wet beriberi with heart failure, dry beriberi with nerve damage, or a combination of these two.

3) Digestive Symptoms

In rare cases, thiamine deficiency can manifest with digestive symptoms such as nausea, vomiting, and stomach pain. Scientists coined the term “gastrointestinal beriberi” to describe such cases, which are more common among infants [68, 21].

Severe cases in infants cause pale or purple skin, swelling, and eventually convulsions and heart failure [18, 69, 70].

4) Lactic Acidosis

The lack of thiamine shifts your cells to anaerobic metabolism (energy production without oxygen), which results in lactate accumulation. Over a long period of time, this process can lead to a dangerous metabolic disorder called lactic acidosis [71, 72].

Toxic amounts of lactate contribute to a range of beriberi symptoms, such as nerve damage and heart failure [71].

Most patients with thiamine deficiency have elevated lactate in their blood and urine; this makes lactate a useful lab marker to confirm the diagnosis [73, 74].

Thiamine deficiency raises your lactate levels and may lead to lactic acidosis, which contributes to nerve and heart damage.

5) Brain Damage

The brain is particularly sensitive to the lack of vitamin B1. Deficiency causes oxidative stress, inflammation, lactic acidosis, and nerve damage. If energy production remains compromised and thiamine stays low, brain cells will die [75, 76].

Wernicke’s encephalopathy is a type of life-threatening brain damage caused by thiamine deficiency. The most common symptoms include [77, 63, 28]:

  • Uncontrolled eye movements
  • Eye muscle weakness
  • Double vision
  • Lack of coordination
  • Confusion

Wernicke-Korsakoff Syndrome

If left untreated, Wernicke’s encephalopathy can progress into psychosis with memory loss, known as Korsakoff syndrome. Once the disease progresses this far, brain injuries are permanent and often end in death [78, 79].

Wernicke-Korsakoff syndrome, also called wet brain, is a transitional state between Wernicke’s encephalopathy and Korsakoff syndrome, with mixed features of both [80].

These conditions are most common in alcoholics, and they greatly contribute to alcohol-induced brain damage and delirium. However, Wernicke-Korsakoff syndrome can also develop in other cases of thiamine deficiency [1].

Thiamine deficiency can cause brain damage known as Wernicke’s encephalopathy, which may progress into life-threatening Korsakoff syndrome.

Conditions Linked to Thiamine Deficiency

Mild thiamine deficiency won’t harm the organs instantly, but in the long run, it may increase the risk of various health disorders.

1) Diabetes

Thiamine is essential for glucose metabolism; deficiency can impair insulin secretion and contribute to diabetes [81, 82].

In diabetes, toxic glucose levels damage the blood vessels. Thiamine deficiency intensifies the problem by causing inflammation and oxidative stress [83].

As a result, the lack of this vitamin can increase LDL cholesterol, total cholesterol, and triglycerides while reducing beneficial HDL cholesterol [84, 47].

The lack of thiamine can also prevent insulin secretion and worsen diabetes complications. Optimal thiamine intake may prevent major diabetes complications, including [85, 86, 87]:

  • Nephropathy (kidney damage)
  • Retinopathy (eye damage)
  • Neuropathy (nerve damage)
Thiamine deficiency impairs glucose control, raises blood lipids, and increases the risk of complications in diabetic patients.

2) Heart Disease

A meta-analysis of 9 clinical trials found that thiamine deficiency is 2.5 times more common among patients with heart failure. They often lack this vitamin due to diuretic use, malnutrition, and alcoholism [88, 64].

In some of these patients, thiamine deficiency may further impair heart function and worsen their symptoms. A review of clinical and animal trials confirmed the role of thiamine deficiency in the development of heart disease [89, 90].

Supplementation with this vitamin may boost heart function and improve other symptoms of heart failure in deficient patients, but the available research is limited [91, 92].

Thiamine deficiency is common among heart failure patients, and it can worsen their symptoms. Supplementation may improve heart function in deficient patients.

3) Mental Disorders

Vitamin B1 enables the production of neurotransmitters such as glutamate, acetylcholine, and serotonin. Flawed or reduced neurotransmitters can impact mental health and raise the risk of depression [93].

Oxidative stress and mitochondrial dysfunction induced by thiamine deficiency can harm the hippocampus, the brain’s hub for memory and emotions [94].

In over 1,500 elderly Chinese people, those with the lowest levels of thiamine had three times higher rates of depression, compared with those with the highest levels [95].

Thiamine (50 mg/day for 2 months) boosted mental clarity and energy in 120 healthy women. Further studies should evaluate the therapeutic effects of thiamine supplementation on mental health [96].

Thiamine deficiency may deplete neurotransmitters and hinder mental health, but the available research is limited.


So far, we’ve discussed a few ways that thiamine deficiency can cause brain damage. These mechanisms might also play a role in autism spectrum disorders (ASD) [97].

In a study of 48 children, those with ASD had 24% lower blood thiamine levels. Infants with thiamine deficiency may face problems with language development as they grow older [98, 99].

However, the available clinical data is limited and far from conclusive. Autism is a complex developmental disorder, and we still don’t know much about causes and contributing factors.

Well-designed clinical studies should cast more light on the potential connection between autism and thiamine deficiency. There are no confirmed benefits of thiamine supplementation for autistic children.


According to some observational data, thiamine deficiency may be linked with dementia. However, there’s still no clinical evidence to support these preliminary observations.

Vitamin B1 deficiency can cause memory loss, with lesions and plaques as seen in Alzheimer’s disease [100, 101, 102].

Patients with Alzheimer’s and other brain diseases often lack thiamine and have reduced activity of thiamine-dependant enzymes in their brains [103, 104].

In preliminary trials, supplementation with thiamine or benfotiamine has produced promising results for this condition. However, these trials included only a handful of patients and had other design flaws. A more recent review concluded there’s not enough data to evaluate the efficacy of thiamine supplementation for Alzheimer’s disease [105, 106, 107, 108].

Diagnosis & Tests

Thiamine Blood Test

Normal thiamine blood levels depend on the lab method and literature source, but they usually range between 70-180 nmol/L of thiamine diphosphate (TDP) or thiamine pyrophosphate (TPP) [7, 8].

When interpreting lab results, consult with your doctor and pay attention to:

  • Units (nmol/L vs. ng/mL)
  • Vitamin forms (free thiamine vs. thiamine diphosphate)
  • Samples (blood vs. red blood cells)

Limitations and Other Tests

Blood (serum) thiamine levels represent only a small portion of the total thiamine in your body and are not a reliable indicator of your overall thiamine status.

Other, more reliable lab markers include erythrocyte transketolase activity and RBC (red blood cells) thiamine diphosphate, but these tests are more expensive and don’t give quick results [64, 29].

Your doctor may also perform a physical exam and look for deficiency symptoms. Rapid improvement with thiamine supplementation usually confirms the diagnosis [61, 8].

Thiamine blood levels below 70 nmol/L may indicate a deficiency. Other lab markers, physical examination, and treatment response can help confirm the diagnosis.

Thiamine Deficiency Treatment and Prevention

People at risk of thiamine deficiency – such as alcohol abusers, pregnant women, and diabetics – should speak to their doctor about dietary changes, supplements, and monitoring their thiamine levels.


A doctor will initiate prompt treatment with intravenous or intramuscular thiamine (50-200 mg) in suspected thiamine deficiency. Doses can be even higher in suspected Wernicke-Korsakoff syndrome. if the symptoms resolve, the maintenance therapy follows with lower doses, oral or injected [61, 8].

Thiamine has a good safety profile, and doctors are encouraged to start the treatment as soon as they suspect a deficiency, instead of waiting for a definite diagnosis. Milder symptoms usually resolve promptly without permanent consequences [61].


If you notice the symptoms of nerve damage and suspect thiamine deficiency, seek medical attention immediately. The following natural approaches are meant to ensure adequate thiamine intake and prevent deficiency, not to treat a condition.

You can boost thiamine naturally by eating more thiamine-rich foods, such as [2, 109]:

  • Whole grains
  • Pork
  • Tuna
  • Soybeans
  • Sunflower seeds
  • Peas

Tea and coffee contain thiaminase enzymes that destroy thiamine; consume them in moderation and try to separate them from your meals [61].

An average adult needs 1.1–1.2 mg of thiamine daily, while the requirements during pregnancy and breastfeeding are slightly higher at 1.4 mg [110].

You may also want to include the following magnesium-rich foods into your diet [111, 112, 113]:

  • Whole grains
  • Leafy greens (spinach, Swiss chard)
  • Beans
  • Nuts (almonds and cashews)

If you’re struggling to maintain optimal levels with balanced nutrition, consider taking magnesium and thiamine supplements.

To cut your risk of deficiency, refrain from drinking alcohol and try to keep your weight in check [114, 79, 36, 35].

To boost thiamine intake, eat a variety of whole grains, seeds, and legumes. Avoid drinking tea or coffee with meals, increase your dietary magnesium, and avoid drinking alcohol.

Buy Vitamin B1


Most healthy people get enough thiamine (vitamin B1). In developed countries, thiamine deficiency is rare and mostly occurs in people who abuse alcohol. Obesity, digestive disorders, diabetes, and heart failure may also increase the risk.

Initial symptoms include confusion, vomiting, nausea, and muscle cramps. Severe deficiency causes leg numbness, tingling, lack of coordination (dry beriberi) and heart failure (wet beriberi). It can eventually lead to permanent brain damage and raise the risk of dementia, diabetes, and heart disease if left untreated.

To increase thiamine intake, eat a variety of whole grains, seeds, and legumes. Avoid drinking tea or coffee with meals, increase your dietary magnesium, and avoid drinking alcohol.

Your doctor will perform a physical exam, run several blood tests, and initiate medical treatment if they suspect deficiency.

About the Author

Aleksa Ristic

Aleksa Ristic

MS (Pharmacy)
Aleksa received his MS in Pharmacy from the University of Belgrade, his master thesis focusing on protein sources in plant-based diets.  
Aleksa is passionate about herbal pharmacy, nutrition, and functional medicine. He found a way to merge his two biggest passions—writing and health—and use them for noble purposes. His mission is to bridge the gap between science and everyday life, helping readers improve their health and feel better.


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