Thiamine (Vitamin B1): The Forgotten Vitamin That Powers Your Brain and Body

B1 Thiamine - the forgotten nutrient.

If you've been struggling with fatigue, brain fog, dizziness, anxiety, migraines, rapid heart rate, digestive issues, or exercise intolerance, you've probably had dozens of blood tests. You've likely had your thyroid, vitamin D and B12 checked. Maybe even iron. But there's one vitamin that is rarely discussed despite playing one of the most fundamental roles in human biology: Vitamin B1, also known as thiamine.

While thiamine isn't the answer for every person with chronic illness, emerging research suggests that inadequate thiamine intake, impaired absorption, increased requirements, or altered utilization may contribute to symptoms in certain individuals. Understanding its role can help patients and clinicians think more broadly about the body's energy systems.

Your Body Runs on ATP; And Thiamine Helps Make It

ATP = adenosine triphosphate

Every cell in your body depends on a tiny molecule called ATP (adenosine triphosphate). ATP is your body's energy currency. Without it, your brain cannot think clearly, your heart cannot pump efficiently, your nerves cannot communicate properly, and your muscles fatigue quickly.

Thiamine acts as a critical cofactor for enzymes that convert carbohydrates into usable cellular energy inside the mitochondria—the "power plants" of our cells. Without enough functional thiamine, the body becomes less efficient at producing energy, even if calories are plentiful.

This helps explain why symptoms of thiamine insufficiency can affect multiple organ systems at once.

Why the Brain Is Especially Sensitive

Although the brain represents only about 2% of body weight, it consumes roughly 20% of the body's energy. That means even subtle disruptions in energy production may disproportionately affect the nervous system. Research has shown that thiamine deficiency can impair neuronal function, increase oxidative stress, alter neurotransmitter production, and reduce mitochondrial efficiency. Severe deficiency is known to cause neurological disorders such as Wernicke encephalopathy, but milder or functional insufficiency may present with far less obvious symptoms.

The brain represents only about 2% of body weight, it consumes roughly 20% of the body's energy.

Patients may report:

• Brain fog

• Difficulty concentrating

• Memory problems

• Anxiety

• Irritability

• Fatigue

• Poor stress tolerance

These symptoms are nonspecific and can have many causes, which is why a thorough medical evaluation is essential.

Chronic Illness Can Increase Thiamine Needs

Many chronic conditions are associated with increased metabolic demands or factors that may affect thiamine status. Examples include:

• Chronic inflammation

• Diabetes

• Gastrointestinal disorders affecting absorption

• Bariatric surgery

• Heavy alcohol use

• Certain medications (such as loop diuretics)

• Diets low in nutrient density

  
  

Some researchers have also proposed that prolonged illness, infections, oxidative stress, and mitochondrial dysfunction may increase the body's need for thiamine, although more research is needed in many of these areas.

Could Blood Levels Miss the Problem?

One of the challenges is that routine blood testing may not always reflect how well thiamine is functioning inside cells. Several specialized laboratory methods, including erythrocyte transketolase activity and thiamine diphosphate measurements, have been used in research settings, but these tests are not routinely performed in clinical practice and each has limitations. This is one reason clinicians may consider the entire clinical picture rather than relying on a single laboratory value.

What About POTS, Dysautonomia, and Fatigue?

Several small studies and case reports have suggested that thiamine supplementation may improve symptoms in selected patients with conditions such as fatigue syndromes, inflammatory bowel disease, and some forms of dysautonomia. Researchers continue to investigate whether impaired cellular energy production contributes to these disorders. These findings are promising but should be interpreted cautiously. Larger, high-quality clinical trials are still needed before broad conclusions can be made.

Best B1 foods

Food First

Thiamine is naturally found in many foods, including:

• Pork

• Beans and lentils

• Sunflower seeds

• Peas

• Whole grains

• Trout

• Fortified cereals

• Nuts

A varied diet remains the foundation of good nutrition.

Should Everyone Take High-Dose Thiamine?

Not necessarily. Thiamine is generally considered safe because excess amounts are excreted in the urine, but that does not mean high-dose supplementation is appropriate for everyone. Different forms of thiamine (such as thiamine hydrochloride, benfotiamine, and thiamine tetrahydrofurfuryl disulfide [TTFD]) have different properties, and dosing should be individualized based on a person's medical history, medications, and clinical goals. If you're considering supplementation, discuss it with a qualified healthcare professional, especially if you have complex medical conditions or take prescription medications.

The Bottom Line

Chronic disease is rarely caused by a single nutrient deficiency. However, chronic illness often places extraordinary demands on the body's energy-producing systems.

Thiamine is one of the most important nutrients involved in converting food into usable cellular energy, making it an important, but often overlooked, piece of the puzzle. For some patients, identifying and correcting inadequate thiamine status may be one component of a comprehensive approach that also addresses sleep, nutrition, inflammation, exercise, medications, hormones, gut health, and underlying medical conditions.

Sometimes better health doesn't come from finding one miracle treatment. Sometimes it begins by making sure the body has the tools it needs to produce energy in the first place. Learn more about the different supplements here: https://us.fullscript.com/plans/jmeinhardt-thiamine-supplements