What Are the Effects of a Vitamin B1 Deficiency?

Many vitamins and minerals are essential for maintaining a well-functioning body, and one of the lesser known heroes of this mix is vitamin B1, also known as thiamine. Vitamin B1 supports the metabolism, psychological health, nerve function and your cardiovascular system – but the body doesn’t produce enough by itself, so you have to ingest it through your diet.1

A vitamin B1 deficiency occurs when you don’t get enough from the foods you eat, or if something is affecting how you absorb nutrients through your gut. Serious thiamine deficiencies are rare in the developed world, but it is still possible – and some people might not even realise the fact for a long period of time.²

In this article, we’ll discuss what a vitamin B1 deficiency looks like and how it can happen in the modern world. Keep reading to learn more.

What Is a Vitamin B1 Deficiency?

A vitamin B1 deficiency occurs when the body does not have enough thiamine to support its normal metabolic and neurological functions. Thiamine plays a key role in converting carbohydrates into usable energy and in maintaining healthy nerve transmission.¹ Without enough thiamine in the blood, these processes become less efficient, which can gradually affect multiple body systems.

Deficiency is usually diagnosed after a review of your symptoms and dietary history, plus analysis of blood and urine to check thiamine levels.² Different people need different amounts of thiamine intake in order to function well, but doctors can assess factors like your age, medical history and lifestyle to determine whether you are deficient.3

What Causes a Deficiency of Vitamin B1?

There are several possible reasons why vitamin B1 levels may fall too low, and it’s not always about your diet.

Inadequate dietary intake

Vitamin B1 is found in foods such as whole grains, legumes, nuts, seeds, pork and fortified cereals.¹ If your diet relies heavily on refined grains or processed foods, you may lack enough thiamine and be vulnerable to deficiency.¹

Malabsorption and digestive issues

Even if you get enough thiamine in your diet, your body might not be the best at absorbing it. Some gastrointestinal conditions such as coeliac disease, inflammatory bowel disease or chronic diarrhoea can interfere with nutrient absorption – essentially preventing you from getting all the benefits from your diet.⁴

Certain medications may also reduce thiamine absorption or cause your body to get rid of too much of it, further increasing the risk of low levels.¹

Increased requirements

Some people need more vitamin B1 than others. Periods of rapid growth, pregnancy, intense physical activity and recovery from illness can all increase the body’s demand for thiamine.¹ If dietary intake does not rise to match this increased requirement, deficiency may develop gradually.

Depending on the situation, this deficiency may resolve itself in time. For example, if illness recovery is a cause, your increased needs may then drop again once you’re fully recovered.

For prolonged situations like pregnancy, though, intervention may be needed to properly support your health.

Underlying health conditions and lifestyle factors

Long-term alcohol consumption is one of the most significant risk factors for thiamine deficiency.

Alcohol interferes with both the absorption and storage of vitamin B1 and can impair its activation within the body.³ In addition, people with chronic medical conditions, metabolic disorders or those undergoing certain medical treatments may be more vulnerable to low thiamine levels.²

Worried this might be the case for you? You can speak to a pharmacist or doctor about the impacts of any underlying conditions you have or medications you take.

Understanding the underlying cause of your deficiency is important, as addressing contributing factors can often be just as important as restoring vitamin levels through supplementation.

What Are the Symptoms of Low Vitamin B1 Levels?

Historically, extreme manifestations of what is now recognised as a vitamin B1 deficiency have included beriberi and Wernicke-Korsakoff Syndrome amongst other conditions – a number of which impact both cardiovascular and neurological systems.³ While these now preventable conditions are considered relatively uncommon in modern populations, they may be seen in at-risk populations.²

But what about more common deficiency symptoms? What you experience can vary depending on how little thiamine you get and how long you’ve been deficient. In early or mild cases, the signs may be vague and easily overlooked.

Fatigue and reduced energy

Because thiamine is essential for energy metabolism, one of the most common early symptoms of deficiency is a persistent tiredness. You may find yourself feeling unusually fatigued even when you’re getting enough sleep.¹

Neurological and cognitive changes

Vitamin B1 is critical for normal nerve function. Low levels may contribute to tingling or numbness in the hands and feet, difficulty concentrating, memory problems or irritability.²

In more serious deficiencies, coordination and balance may also be affected.³

Muscle weakness and physical discomfort

Efficient muscle function depends on proper nerve signalling and energy production. As a result, deficiency may lead to muscle weakness, cramps or a general sense of physical heaviness.¹

Cardiovascular effects

In more severe or prolonged deficiencies, the heart may be affected. If your cardiac function is reduced, this may present as:

Unusual shortness of breath
Heart palpitations or a pounding in your chest
Swelling in your lower legs.3

These symptoms reflect the increased strain placed on the cardiovascular system when thiamine-dependent energy processes are disrupted.

Digestive and appetite changes

Some individuals with low vitamin B1 levels report reduced appetite, nausea or general digestive discomfort.² Unfortunately, experiencing these symptoms can cause you to eat less often and limit your variety of foods – all of which can further limit nutrient intake, potentially worsening the deficiency over time.

If any of this sounds familiar and you think your symptoms might be related to low vitamin B1 levels, it’s important not to self-diagnose. Many of these symptoms can also be linked to other nutritional deficiencies or underlying medical conditions.

To get the right help for your situation, speak to a doctor about your symptoms. If you do have a thiamine deficiency, they’ll be able to help you find the right solution for you.²

Supporting Your Intake of Vitamin B1

To make sure you get enough vitamin B1, it’s crucial to eat a healthy, varied and balanced diet. It’s also helpful to understand the factors that can increase your thiamine needs so you know what to expect if the situation arises.¹

If you need to supplement your thiamine intake, the easiest way to do so is by taking a vitamin B complex – a combination supplement that includes various B vitamins to ensure healthy levels of them all. By looking after your diet and, if needed, supplementing responsibly, you can support your overall health and wellbeing and avoid deficiency.

References

National Institutes of Health, Office of Dietary Supplements. (2023). Thiamin (Vitamin B1) – Fact Sheet for Health Professionals. https://ods.od.nih.gov/factsheets/Thiamin-HealthProfessional/
NHS. (2022). Vitamins and minerals – B vitamins. https://www.nhs.uk/conditions/vitamins-and-minerals/vitamin-b/
Lonsdale, D., & Marrs, C. (2017). Thiamine deficiency disease, dysautonomia, and high calorie malnutrition. Academic Press. https://doi.org/10.1016/C2015-0-01598-6
World Health Organization. (1999). Thiamine deficiency and its prevention and control in major emergencies. https://apps.who.int/iris/handle/10665/66139