Vitamin B1 (Thiamine)

Vitamin B1, also known as thiamine, is a nutrient many people recognise from cereal labels or multivitamin packaging, yet few fully understand what it does. Unlike trend-driven supplements, thiamine works quietly in the background, supporting everyday processes such as energy production and nerve function.

For most people in the UK, a balanced diet provides all the thiamine needed. However, certain lifestyles, medical conditions, and medications can increase the risk of low levels. This guide explains what vitamin B1 does, who may need to pay closer attention to their intake, and when it’s worth speaking to a pharmacist.

What Is Vitamin B1 (Thiamine)?

Vitamin B1 is one of the eight B vitamins and is classed as water-soluble. This means the body does not store large reserves of it. Any excess is excreted in urine, so thiamine needs to be consumed regularly through food or supplements.

Because the body cannot make thiamine on its own, it must come from the diet. The daily requirement is relatively small - around 1mg per day for men and slightly less for women - but meeting that requirement consistently is important for normal bodily function.

What Does Vitamin B1 Do in the Body?

Thiamine’s most important role is helping the body convert carbohydrates into energy. Every cell relies on this process, particularly those in the brain, nerves, heart, and muscles.

It also plays a key role in maintaining healthy nerve signalling. When thiamine levels are adequate, nerves can transmit messages efficiently between the brain and the rest of the body. This helps support normal sensation, movement, and coordination.

The heart is especially dependent on thiamine because it requires a constant supply of energy to function properly. Adequate thiamine supports normal heart muscle activity and overall cardiovascular function.

In everyday terms, vitamin B1 helps:

Turn food into usable energy
Support normal nerve function
Help the heart and muscles work efficiently

Signs of Low Vitamin B1

Early symptoms of low thiamine can be subtle and are often mistaken for stress, ageing, or general fatigue. Because thiamine is involved in energy production and nerve health, symptoms often affect these systems first.

Common signs may include:

Persistent tiredness or low energy
Poor concentration or "brain fog"
Tingling or numbness in hands or feet
Reduced appetite or unexplained weight loss

If deficiency becomes more severe and prolonged, serious conditions such as beriberi or Wernicke encephalopathy can develop. These are now uncommon in the UK but can occur in people with significant risk factors, particularly long-term alcohol dependence or severe malnutrition.

Who Is More Likely to Be Low in Thiamine?

Most people meet their thiamine needs through food, but some groups are more vulnerable to deficiency due to reduced intake, absorption problems, or increased losses.

People at higher risk include:

Those who drink alcohol heavily or regularly
Older adults, especially those with limited diets
People with digestive conditions such as coeliac disease or Crohn’s disease
Individuals who have had bariatric (weight-loss) surgery
People taking long-term diuretics or certain other medications

Severe vomiting, eating disorders, and prolonged poor intake can also lead to deficiency surprisingly quickly, as the body’s thiamine stores are limited.

Food Sources of Vitamin B1

Thiamine is widely available in everyday foods, making deficiency uncommon in people with varied diets.

Good dietary sources include:

Wholegrains such as wholemeal bread, oats, and brown rice
Pork and other meats
Beans, lentils, nuts, and seeds
Fortified breakfast cereals and white flour products

In the UK, non-wholemeal wheat flour is legally fortified with thiamine, which helps protect the wider population from deficiency even when refined grains are consumed.

Vitamin B1 Supplements: Are They Necessary?

For most people, supplements are not needed. A balanced diet usually provides sufficient thiamine without additional support.

Supplements may be appropriate for:

People with diagnosed thiamine deficiency
Individuals with absorption problems or after bariatric surgery
Those with alcohol dependence, where routine supplementation is often advised

Thiamine is available on its own, as part of B-complex products, or within multivitamins. Standard oral doses are generally considered safe, and higher doses may be prescribed by healthcare professionals for specific medical reasons.

Supplements should support - not replace - good dietary intake.

Can You Take Too Much Vitamin B1?

Because thiamine is water-soluble, excess amounts are usually excreted in urine rather than stored in the body. This makes toxicity very unlikely at normal supplement doses.

Most people tolerate thiamine well. Mild digestive upset can occasionally occur, and allergic reactions are rare. The NHS advises that daily doses of up to 100mg are unlikely to cause harm when taken as directed.

Taking more than needed does not provide extra benefits if you are not deficient.

When to Speak to a Pharmacist or GP

A pharmacist can help assess whether thiamine supplementation may be appropriate and check for possible interactions with other medicines.

It’s sensible to seek advice if:

Symptoms such as fatigue or tingling persist
You have a long-term medical condition
You take regular prescription medicines
You’re considering long-term supplementation

More serious symptoms such as confusion, vision changes, or severe weakness require prompt medical assessment.

Pharmacist comment

"Vitamin B1 deficiency is uncommon in people eating a varied diet, but we do see it in specific situations such as alcohol dependence, digestive conditions, or after bariatric surgery. A pharmacist can help identify when supplementation may be appropriate and when further medical assessment is needed." -Alessandro Grenci, Superintendent Pharmacist

Conclusion

Vitamin B1 may not attract much attention, but it plays an essential role in energy production, nerve health, and heart function. Most people in the UK meet their needs through diet alone, helped by food fortification and widespread availability of thiamine-rich foods.

Certain groups are more vulnerable to deficiency, and for them, supplementation can be an important preventative measure. When in doubt, pharmacists offer accessible, expert advice to help ensure supplementation is safe, appropriate, and tailored to individual needs.

Sources

Written by Christian Jakobsson