Thiamine deficiency - when the body's energy factory stops

Do you feel unusually tired, shaky in the legs, dizzy or “foggy” in the head without really understanding why? Sometimes such symptoms are not just about stress or lack of sleep, but about nutritional deficiencies that affect the most basic functions of the body. Vitamin B1 (thiamine) is one such substance: a small but crucial vitamin that is needed for the nervous system, heart and metabolism to function normally. When levels become too low, the symptoms can be diffuse at first – but in some cases serious if the deficiency is not detected in time.

What is vitamin B1 (thiamine)?

Vitamin B1 (thiamine) is a water-soluble vitamin that the body needs to convert carbohydrates into energy. It functions as a coenzyme, i.e. a helper molecule, in several important biochemical processes. Simply put, thiamine helps cells “get” usable energy from the food we eat. The brain, nerves, muscles and heart in particular depend on it. Since the body only stores small amounts of thiamine for a limited time, deficiency can develop relatively quickly in the event of insufficient intake, poor absorption or increased loss.

This is also why vitamin B1 deficiency can sometimes occur in situations where you do not spontaneously think of a vitamin deficiency, for example in the event of prolonged vomiting, high alcohol consumption, rapid weight loss, after bariatric surgery or in certain medical conditions that affect the intestines and nutrient absorption.

What does vitamin B1 do in the body?

Thiamine is needed primarily for:

• Energy metabolism – helps the body use carbohydrates as fuel
• Nerve function – supports normal signal transmission in the nerves
• Brain function – the brain is very sensitive to thiamine deficiency
• Heart function – the heart muscle needs energy continuously and is affected by a deficiency

When the body lacks thiamine Tissues with high energy needs are particularly affected. This is why you can experience tingling, muscle weakness, balance problems, memory problems or heart problems if you have a pronounced deficiency.

Symptoms of vitamin B1 (thiamine) deficiency

Early symptoms of thiamine deficiency are often non-specific, which means they can easily be misinterpreted as something else. For example, you may feel:

• fatigue or lack of energy
• irritability
• poor concentration or memory
• decreased appetite
• stomach upset or discomfort
• sleeping difficulties

In more pronounced deficiencies, the symptoms may become more pronounced and are often divided into different clinical pictures:

• Dry beriberi – primarily affects the nerves and can cause tingling, numbness, burning feet, muscle weakness, cramps and difficulty walking
• Wet beriberi – primarily affects the heart and circulation and can cause swelling, shortness of breath, palpitations and heart failure symptoms
• Wernicke's encephalopathy – an acute neurological condition that can cause confusion, unsteadiness and eye movement disorders
• Korsakoff's syndrome – a serious memory condition which can occur if severe deficiency is not treated in time

It is important to know that not everyone gets the "full textbook" of symptoms. For example, one person may seek treatment for numbness in the feet, another for prolonged fatigue, and a third for dizziness and difficulty walking after a period of vomiting or severe weight loss. Therefore, the symptoms always need to be assessed in their context.

Why does vitamin B1 deficiency occur?

The most common cause globally is too low intake through the diet. It is often the combination of several risk factors that plays a role. Examples of common causes are:

• High alcohol consumption - alcohol can both reduce the intake of nutritious food and impair the absorption of thiamine
• Prolonged vomiting - for example, in case of stomach disease, morning sickness or after surgery
• Malabsorption - diseases or conditions in which the intestine does not absorb nutrients normally
• Bariatric surgery - especially if you also have difficulty eating or are vomiting
• Malnutrition or a one-sided diet
• Dialysis or other conditions with increased loss of water-soluble vitamins
• Increased need - for example, during pregnancy, breastfeeding, rapid growth or prolonged fever

An important medical principle is that carbohydrate intake can worsen an ongoing severe thiamine deficiency. If a person with a pronounced deficiency receives a lot of glucose, for example in connection with refeeding after malnutrition or via a drip, the body's need for thiamine increases and the risk of neurological complications may increase. This is the reason why healthcare pays particular attention to thiamine in cases of malnutrition, alcohol dependence, prolonged vomiting and refeeding syndrome.

How do you get vitamin B1 – and is the food always enough?

Vitamin B1 is found naturally in several foods, including:

• whole grain products
• legumes
• pork
• nuts and seeds
• certain fortified cereal products

The need for thiamine is closely related to energy intake. European reference values ​​are therefore often expressed as an amount per energy unit, and for adults a population reference intake of 0.1 mg per MJ is given, which corresponds to approximately 0.4 mg per 1,000 kcal. For most people who eat a varied diet, the need is covered through diet, but this does not always apply in the event of illness, a one-sided diet or reduced absorption.

Many people wonder: “Can I just take a dietary supplement instead of getting tested?” In some cases, a regular B vitamin preparation may be reasonable as a supplement, but it is not always sufficient – ​​and it must not replace medical assessment if a clear deficiency is suspected. In the case of neurological symptoms, prolonged vomiting, high alcohol consumption or after bariatric surgery, rapid treatment in a higher dose and sometimes intravenously may be needed.

There is no set upper limit for thiamine intake from food or regular dietary supplements, since no clear toxicity has been shown when taken orally. At the same time, this does not mean that self-treatment is always the right path. The important thing is to understand why a possible deficiency has arisen.

When should you test for vitamin B1 (thiamine)?

It is wise to consider testing or medical evaluation if you:

• have prolonged fatigue without a clear explanation
• experience tingling, numbness or muscle weakness
• have balance problems or unexplained dizziness
• have had prolonged vomiting or severe weight loss
• have undergone bariatric surgery
• have high alcohol consumption
• have conditions that affect nutrient absorption or nutrition

Testing for vitamin B1 (thiamine) can be a way to get a clearer picture, but laboratory diagnostics always need to be interpreted together with symptoms, diet, medical history and other test results. In practice, different methods are used, for example measuring thiamine in whole blood or assessing functional markers in red blood cells. Since analysis methods and reference ranges can differ between laboratories, it is important that the result is assessed in the right context.

It is also common to need to review other nutrients at the same time. Someone who has a deficiency in vitamin B1 may also have low levels of, for example, vitamins B12, folate, iron, magnesium or vitamin D, especially in cases of malnutrition, intestinal problems or after weight loss surgery. Therefore, a broader checkup can sometimes provide more information than a single sample. This is particularly valuable for people who want to understand the cause behind diffuse symptoms.

However, there is an important distinction to make: if you or someone close to you has confusion, difficulty walking, eye movement disorders, severe weakness, heart involvement or increasing neurological symptoms, then it is not a matter of "just ordering a test". In this case, you should seek urgent care, as severe thiamine deficiency may require immediate treatment.

Understanding your nutritional status is part of preventive health. For some, a better diet is enough, for others, targeted treatment and follow-up are needed. The important thing is not to ignore symptoms that are ongoing or worsening.