19 Unmissable Signs You're Running Low on Thiamine

Thiamine, also known as vitamin B1, is an essential nutrient that plays a critical role in converting food into energy and supporting the function of nearly every cell in the body. Unlike some vitamins that can be stored long-term, thiamine must be regularly consumed through diet or supplements, as the body cannot produce it on its own. When thiamine levels drop too low, a deficiency can develop, leading to a wide range of symptoms that affect the nervous system, heart, muscles, and brain. Thiamine deficiency can occur for many reasons, including chronic alcohol consumption, diabetes, gastrointestinal disorders, bariatric surgery, and aging. Left untreated, it can lead to serious health complications, including neurological damage and cardiovascular issues. Because thiamine deficiency symptoms often mimic other conditions, it can go unnoticed for a long time. To help you recognize the warning signs, we’ve expanded our list to 19 unmissable symptoms that may indicate you're running low on this essential vitamin.

1. Shortness Of Breath

Thiamine deficiency can cause problems with the heart and making it beat too slow. Putting this kind of stress on the heart can result in shortness of breath and fatigue. Just like many other symptoms of a thiamine deficiency can be caused by various reasons, being short of breath can be indicative of other illnesses. It is important, then, for doctors to evaluate this with other symptoms patients might be having. A thiamine deficiency can also lead to heart failure because the heart is working too hard to pump the blood through the body. When this happens, fluid can accumulate and make it harder to breathe and results in being short of breath. The extra work being forced on the heart can also contribute to other symptoms, like fatigue.

2. Blurry Vision

It is important if a patient experiences blurry vision, and there are other contributing factors, that they have their thiamine levels checked. A severe thiamine deficiency can cause the optic nerve to swell, which can cause problems with the patient's vision, such as blurriness, and can even result in the loss of vision. However, there is a significant chance vision problems will lessen when the thiamine deficiency is corrected. Vision issues such as blurry vision can also be linked to problems in the brain because the thiamine deficiency can affect the nerves and other parts of the brain.

3. Tingling In The Arms And Legs

Tingling in the arms and legs is called paresthesia, which is different from when individuals experience their limbs 'going to sleep' because they have been put in an awkward position that cuts off blood flow. The sensation of 'pins and needles' goes away as circulation is returned to the area. Paresthesia is more concerning. A thiamine deficiency can damage the peripheral nerve, and if the peripheral nerve is damaged, it can make it difficult to walk or hold onto things. Paresthesia in a leg makes it incredibly difficult for individuals to walk. It is important for patients with ongoing episodes of paresthesia to consult a doctor, especially if they are experiencing other symptoms.

4. Fatigue And Irritability

Many illnesses and diseases cause fatigue and irritability, so it is easy to dismiss it and not consider thiamine deficiency. A thiamine deficiency can cause fatigue to come on suddenly but can also occur over an extended period. The body works hard to convert food into energy, and when there is a deficiency of thiamine, which is essential in this conversion, the body is working extra hard. This can lead to fatigue, and along with fatigue can come irritability. When the body is fatigued, it is more difficult to remain in a good state of mind. Just like fatigue, irritability can be associated with many different conditions, but when they are present alongside other symptoms on this list, a thiamine deficiency is a real possibility.

5. Lack Or Loss Of Appetite

One of the most common symptoms of a thiamine deficiency is a lack or loss of appetite. It seems the part of the brain that affects appetite is altered when there is a thiamine deficiency. When individuals have a deficiency in thiamine, their body thinks it is full or satisfied when it is not. This causes less food to be eaten, weight loss, and potential eating disorders. If an individual's body is telling them it does not need food because it is full, the individual will be less inclined to eat. Conversely, there are times the body cannot seem to be satiated and individuals will not be able to get enough food. The problem with a thiamine deficiency is it affects the functioning of the satiety center in the brain and causes problems of being full to being hungry at an extreme level.

6. Swelling In The Legs

Swelling in the legs may be indicative of a thiamine deficiency. This symptom is related to the cardiovascular involvement that occurs with a shortage of thiamine. A thiamine deficiency triggers a cascade of events, including the dilation of blood vessels in an affected individual's limbs. When this occurs, the renin-angiotensin-aldosterone system in the body leaps into action. The detection of volume loss in the blood vessels causes the affected individual's kidneys to react by retaining salt, which leads to the retention of fluids. This mechanism in the body increases blood pressure to prevent ischemic events. However, adverse symptoms can occur as a result of the overactivation of such homeostatic mechanism. Individuals affected by a thiamine deficiency retain significantly higher amounts of salt and fluid in their body, which eventually results in fluid overload. Excess fluid in circulation can be dangerous, so the fluid begins to leak through the blood vessel walls instead of continuing to accumulate in circulation. This mechanism is what causes swelling in the legs due to the force of gravity on the tissues containing this excess fluid.

7. Weight Loss

Thiamine deficiency patients may exhibit weight loss as a symptomatic manifestation of their condition. Carbohydrates are a form of dietary nutrient the body utilizes to produce energy the cells are able to utilize. Weight loss may occur in a thiamine deficiency because the brain's mechanism of mediating low energy states in affected individuals called AMP-activated protein kinase (AMPK) becomes impaired. AMPK in the hypothalamus acts to restore the balance of energy in the body through increasing the production of glucose, stimulating feeding behavior, and stopping thermogenesis to slow the output of energy. However, a thiamine deficiency inhibits the action of AMPK in the hypothalamus, which cripples the mechanism the body uses to keep a balance between energy expenditure and energy intake. Without this balance, the patient will not have an appetite triggered by the AMPK mechanism, and the expenditure of energy at rest will not decrease. This negative energy balance burns away any calories and extra fat around the body during energy-making processes, resulting in obvious weight loss and anorexia in some cases.

8. Compromised Reflexes

Compromised reflexes may be a symptom manifestation of thiamine deficiency. Because thiamine is critical for the metabolism of carbohydrates and proteins, a lack of it means these metabolic processes do not occur as much. As a side effect of this malfunction, the products of carbohydrate synthesis called pyruvic acid and lactic acid accumulate in the tissues and cause the progressive degeneration of nerve cells. The long nerves in the legs are typically affected first, and the long nerves of the arms follow. Because the nerves play a large role in the reflexes, damage to these nerves can result in a loss or reduction of the reflexive functions. Additionally, the wasting of muscle that occurs in individuals who have a thiamine deficiency due to inadequate energy production can contribute to the compromise of reflexes. The reason for this is because the muscle is the tissue that produces movement of the limb in a reflex. Both the muscular and neural components of the reflexes must be functional in order to produce a reflex movement in response to stimuli.

9. Delirium

Individuals who experience delirium may be affected by a deficiency of thiamine. Thiamine is an important vitamin that helps facilitate the conversion of dietary nutrients into cellular energy the body can use. These processes require the use of certain enzymes that depend on the presence of thiamine to work correctly. As a result, there is a reduction in the activities of these enzymes that effectively begins a cascade of metabolic events that compromise significant amounts of energy. Certain tissues in the brain have greater metabolic requirements than other parts. The absence of energy and thiamine in these demanding tissues results in neuronal death. When this process occurs in certain parts of the brain, the patient can experience episodes of delirium. Additionally, a thiamine deficiency commonly results in increased cardiac output and an elevated resting heart rate. Both of these factors over time can result in reduced heart function. When the heart cannot pump efficiently enough or blood pressure becomes too low, not enough oxygen is delivered to the tissues in the brain. This mechanism can also result in an affected individual's delirium.

10. Nausea And Vomiting

Nausea and vomiting is an uncommon symptom manifestation in a thiamine deficiency. The mechanism behind the occurrence of this symptom is similar to what adversely affects the reflexes. A build-up of lactic acid and pyruvic acid in the blood can cause inflammation in the fibers of a nerve the brain uses to communicate with the digestive tract. This nerve is called the vagus nerve, and it is responsible for the stimulation of involuntary movements in the stomach, esophagus, and most of the intestines. These movements help food travel through the gastrointestinal tract. When the vagus nerve becomes inflamed and swollen, it can cause abnormalities in the transmission of signals between the brain and muscles that produce these movements in the stomach and esophagus. When these abnormalities include a spasmodic misfiring of nerve impulses, the esophagus and or stomach can move too much. This abnormal movement can cause the patient to feel nauseated and or vomit as a result of their thiamine deficiency.

11. Memory Problems and Confusion

Thiamine plays a crucial role in brain function, particularly in energy production for neurons and neurotransmitter synthesis. A deficiency in this essential vitamin can cause cognitive issues such as memory loss, difficulty concentrating, and general confusion. Some individuals may experience mild forgetfulness, while others may develop severe impairments, including symptoms resembling dementia. This occurs because the brain requires a constant supply of energy, and without enough thiamine, certain areas of the brain, particularly the hippocampus, which is responsible for memory formation, may not function properly. If left untreated, thiamine deficiency can progress into more severe neurological conditions, such as Wernicke-Korsakoff syndrome, which leads to irreversible memory damage. People who notice persistent brain fog, difficulty recalling information, or episodes of confusion should seek medical evaluation, especially if they have other risk factors for thiamine deficiency.

12. Involuntary Eye Movements (Nystagmus)

A lesser-known but critical symptom of thiamine deficiency is nystagmus, a condition characterized by rapid, involuntary eye movements. These movements may be side to side, up and down, or even rotational, often leading to blurred vision, dizziness, and difficulty focusing on objects. This occurs because thiamine deficiency impacts the cerebellum and brainstem, areas responsible for motor control and eye movement coordination. If untreated, this condition can worsen, making it difficult for individuals to read, drive, or perform daily activities requiring visual precision. In more advanced cases, nystagmus can be an early sign of Wernicke’s encephalopathy, a severe neurological disorder caused by prolonged thiamine deficiency, which can also lead to vision problems, disorientation, and difficulty walking. If someone experiences unexplained eye movement issues alongside other neurological symptoms, they should seek medical attention as soon as possible.

13. Dizziness and Lightheadedness

Thiamine deficiency can interfere with the autonomic nervous system, which regulates involuntary functions such as blood pressure and heart rate. As a result, individuals may experience frequent episodes of dizziness or lightheadedness, particularly when standing up quickly—a condition known as orthostatic hypotension. This happens when the body is unable to properly regulate blood circulation, leading to a sudden drop in blood pressure. The lack of adequate energy production in nerve cells also contributes to poor balance and an increased risk of falls, especially in older adults. In severe cases, chronic dizziness may be accompanied by fainting spells, making routine activities dangerous. Because dizziness can stem from various underlying causes, individuals should consider their overall health and whether they have additional symptoms of thiamine deficiency before seeking medical advice.

14. Muscle Weakness and Cramps

Since thiamine is vital for muscle function and nerve communication, a deficiency can cause persistent muscle weakness, cramps, and even muscle wasting in more advanced cases. Without enough thiamine, the nervous system struggles to transmit signals effectively, leading to impaired muscle contractions and coordination. Many individuals report feeling unusually weak, even after minimal exertion, or experiencing sudden cramps in their legs, feet, or hands. Over time, muscle weakness may worsen, affecting mobility and making simple tasks like climbing stairs or carrying groceries difficult. In extreme cases, individuals with chronic thiamine deficiency may experience severe muscle deterioration, known as muscle atrophy, where the muscles shrink due to lack of use and nutrient supply. Early recognition of these symptoms and proper supplementation can prevent long-term muscular damage and restore normal function.

15. Rapid Heart Rate (Tachycardia)

Thiamine plays a vital role in cardiovascular health, particularly in maintaining proper heart function. A deficiency can lead to an increased heart rate, or tachycardia, as the heart works harder to compensate for the reduced energy supply in the body. This occurs because thiamine is essential for producing adenosine triphosphate (ATP), the energy molecule that fuels the heart muscle. Without it, the heart may struggle to pump efficiently, leading to palpitations, a pounding sensation in the chest, or shortness of breath during routine activities. In some cases, prolonged thiamine deficiency can contribute to heart failure, known as "wet beriberi," a condition where fluid builds up in the heart and lungs due to inefficient circulation. If someone experiences a persistently rapid heart rate along with other symptoms of thiamine deficiency, it is important to seek medical attention promptly.

16. Increased Sensitivity to Noise

An unusual but notable symptom of thiamine deficiency is hypersensitivity to sound. Some individuals report feeling overwhelmed by normal volumes of noise, experiencing discomfort or even pain when exposed to loud environments. This heightened sensitivity is likely due to thiamine’s role in nervous system function, as the vitamin helps regulate nerve signals and sensory processing in the brain. When thiamine levels are low, neurons may become overactive or misfire, leading to an exaggerated response to auditory stimuli. This can make social gatherings, traffic noise, or even simple household sounds distressing. If someone develops an unexpected intolerance to noise alongside other neurological symptoms, a thiamine deficiency could be a contributing factor.

17. Difficulty Speaking or Slurred Speech

As thiamine deficiency affects nerve function in the brain and muscles, it can impact speech clarity and coordination. Individuals may struggle to form words properly, experience slurred speech, or find themselves pausing frequently while trying to articulate thoughts. These speech difficulties are often linked to disruptions in the brainstem, which controls motor functions, including speech. When combined with other neurological symptoms, such as confusion, impaired reflexes, or difficulty walking, speech changes could indicate a more advanced thiamine deficiency leading to conditions like Wernicke’s encephalopathy. If someone develops persistent or worsening speech difficulties, medical evaluation is necessary to rule out underlying neurological causes.

18. Excessive Sweating or Difficulty Regulating Body Temperature

Thiamine plays a role in the autonomic nervous system, which helps regulate body temperature. A deficiency can cause individuals to either sweat excessively without exertion or, conversely, struggle to maintain warmth in cold environments. This occurs because the body’s ability to manage heat production and dissipation is disrupted when nerve signaling is impaired. Some individuals may experience hot flashes, night sweats, or sudden chills, while others might notice their hands and feet feeling persistently cold. These temperature regulation issues may be accompanied by fatigue, dizziness, and an increased heart rate, all of which point to potential metabolic disturbances caused by thiamine deficiency.

19. Mood Changes, Anxiety, or Depression

Since thiamine is crucial for brain function and neurotransmitter regulation, a deficiency can lead to mood disturbances, including increased anxiety, depression, or sudden mood swings. Many individuals with low thiamine levels report feeling more irritable, overwhelmed, or emotionally unstable without a clear reason. This occurs because thiamine is involved in producing neurotransmitters like serotonin and dopamine, which influence mood, motivation, and stress management. When the brain lacks sufficient energy due to thiamine deficiency, it can trigger psychological symptoms that mimic common mood disorders. If someone notices a sudden or unexplained change in their emotional well-being, particularly if accompanied by fatigue, brain fog, or neurological issues, addressing their thiamine intake may help restore mental balance.

Recognizing and Addressing Thiamine Deficiency

Thiamine deficiency can manifest in various ways, often mimicking other conditions, making it challenging to diagnose. However, early recognition of symptoms is key to preventing long-term damage. Whether the deficiency arises from poor diet, chronic illness, alcohol dependency, or metabolic conditions, supplementation and dietary adjustments can help restore healthy thiamine levels. Foods rich in thiamine, such as whole grains, legumes, nuts, and lean meats, can support proper nerve function, muscle health, and cognitive performance. If symptoms persist or worsen, medical professionals can conduct tests to confirm a deficiency and recommend appropriate treatment. By staying aware of these 19 unmissable signs, individuals can take proactive steps toward better health and prevent complications associated with thiamine deficiency.