Vitamin B1: Small Dose, Big Effect: Results of New Review

Vitamin B1 (thiamine) is usually remembered as "anti-beriberi." But a recent review in Nutrients shows that its role is much broader - from key cellular energy nodes to supporting nucleotide synthesis pathways and DNA resistance to damage. The authors remind us that B1 deficiency is underestimated even outside of alcoholism: it is provoked by disease-associated malnutrition, vomiting and gastrointestinal disorders, long-term use of diuretics, monotonous and ultra-processed diets. And if "everything is normal" in the diet, this is not yet a guarantee of optimal status: some people's needs may be higher than the formal norm.

Background of the study

Thiamine (vitamin B1) is a key cofactor of energy metabolism and the "nodes" of the pentose phosphate pathway, but in clinical routine it is remembered mainly in classical deficiency syndromes (beriberi, Wernicke's encephalopathy). Meanwhile, the body is almost unable to store B1 (short half-life, small depots), the needs increase during illness and stress, and modern risk factors - monotonous/ultra-processed diets, malabsorption, postoperative gastrointestinal conditions and barivelix surgery, hyperemesis gravidarum, chronic infections, long-term use of diuretics and some other drugs - make subclinical deficiency much more common than is commonly thought.

Biochemically active forms of thiamine (TDP/TPP and TTP) are the “cogs” of the pyruvate and α-ketoglutarate dehydrogenase complexes, branched-chain α-keto acid dehydrogenase and transketolase. Through them, B1 supports the production of ATP, the synthesis of ribose for DNA/RNA and the formation of NADPH - the basis of antioxidant protection and reparation. Therefore, the deficiency manifests itself in many ways: from fatigue, cognitive “fog” and peripheral neuropathy to cardiomyopathy and deterioration of glycemic control. In parallel, observational data are accumulating on the relationship between low B1 status and the risk of hypertension, type 2 diabetes and depressive symptoms - signals that require verification in randomized trials.

A separate problem is diagnostics. Serum thiamine is uninformative; whole-blood TDP and erythrocyte transketolase activity better reflect the status, but these methods are poorly standardized and not widely available. As a result, doctors focus on non-specific symptoms and risk context, while the “real” needs of some patients may exceed the minimum recommended norms. Against this background, a review of the evidence is needed: who benefits from assessing status/supplementation and when, what doses and forms are justified, what are the targets (energy, PPP/NADPH, neuro- and cardioprotection) and what biomarkers to use in practice. This review closes this gap, systematizing the physiology, risk groups, diagnostic approaches and potential clinical scenarios for the use of thiamine.

What Thiamine Does in the Cell - "Fuel, Repair, Defense"

• In the form of TDP/TPP, it is a coenzyme of the "entry gates" of carbohydrates into the mitochondria (pyruvate and α-ketoglutarate dehydrogenase) and enzymes of the pentose phosphate pathway (e.g. transketolase). This supports the production of ATP, the synthesis of ribose for DNA/RNA and the formation of NADPH - the antioxidant "currency" of the cell.
• Through its effect on PPP/NADPH, thiamine indirectly strengthens antioxidant systems (glutathione/thioredoxin), reducing oxidative stress and helping to maintain DNA integrity.
• In nervous and cardiac tissues, high concentrations of thiamine and its phosphates are associated with stable energy and electrical excitability - another reason why the deficiency manifests itself polysystemically.

The problem is that the body is almost unable to store B1: the half-life is short, and the needs increase during stress and illness. Early symptoms of deficiency - fatigue, "brain fog", irritability, sleep and appetite disturbances - are easily mistaken for "just tired". At the same time, many clinics and studies do not measure thiamine at all - hence the chronic underestimation.

Who should especially think about B1 status

• Patients with diseases and unintentional weight loss, malabsorption, frequent vomiting, after gastrointestinal surgery.
• People on long-term diuretics (eg, for heart failure) or other drugs/chemicals that accelerate the degradation of thiamine.
• With monotonous/restrictive diets and high consumption of ultra-processed foods.
• Special risk groups include pregnant women with hyperemesis and patients with HIV/AIDS.

Adults are traditionally recommended about 1.1-1.2 mg/day. But the review provides data that such a “minimum norm” does not always provide an optimal status, and in a number of clinical scenarios, high doses are studied as an adjuvant: lowering blood pressure in people with hyperglycemia against the background of ≈300 mg/day, improving glucose tolerance in prediabetes, neuroprotection in stroke models, associations of low B1 levels with depressive symptoms. These are not direct prescriptions, but signals for targeted trials and precise stratification.

Biochemistry - Why Sources and Form Matter

• In food, B1 is most often found phosphorylated in animal products and unphosphorylated in plant products; in the intestine, esters are quickly broken down, and absorption in healthy individuals exceeds 95%.
• In the blood, >80% of thiamine is found in erythrocytes in the form of TDP/TTP; tissue “storehouses” are muscles, heart, brain, liver, kidneys.
• In mitochondria, TDP is a cog in the cycles that govern energy, lipid/myelin synthesis, and resistance to oxidative stress.

The practical logic follows from this: maintain a varied diet, monitor symptoms and context (medications, illnesses), and, if there are risks, discuss status assessment with a doctor and, if necessary, supplementation. The review emphasizes that in “modern life,” many factors - from pharmaceutical load to food additives - accelerate B1 consumption, which means that narrow “minimum” norms do not always reflect the patient’s reality.

What else is interesting in the review (and what is still in question)

• Metabolic health: There is evidence that B1 sufficiency is associated with a lower risk of hypertension and type 2 diabetes; high doses have been considered to support glycemic control in prediabetes - a topic for RCTs.
• Brain and vascular: In model studies, thiamine reduced excitotoxicity (glutamate-mediated injury) in stroke; clinical translation requires confirmation.
• Mental health: Low B1 levels are associated with greater depressive symptoms - causality has not been proven, but the direction for research is clear.

This is a review, though: it neatly summarizes disparate data, but it is not a substitute for randomized trials. The authors call for more frequent monitoring of B1 status in risk groups, clarification of “health-related” ranges, standardization of biomarkers, and focusing clinical trials where benefits are most likely—against the background of hyperglycemia, cardiovascular risks, neurological conditions, and malnutrition.

Practical conclusions for the reader

• B1 deficiency is not only about alcohol: illnesses, medications and "fast" diets also dry up the reserve. If you recognize yourself as having a set of "fatigue + fog + appetite/sleep + gastrointestinal tract", especially against the background of risks - a reason to talk to a doctor.
• "1 mg per day" is the lower limit for healthy people; the optimum for a particular person depends on the context. Self-medication with "high doses" without indications and control is not an idea; but ignoring the status in risk groups is also not an idea.
• Eat a varied diet: whole foods, moderate processing, less ultra-processed foods - this protects not only calories and minerals, but also the coenzyme architecture of your metabolism.

Conclusion

Thiamine is a modest dose but critical regulator of energy, antioxidant defense and DNA repair; in today's reality, its deficiency is more common than we usually think and deserves active monitoring and smart correction.

Source: Kaźmierczak-Barańska J., Halczuk K., Karwowski BT Thiamine (Vitamin B1)-An Essential Health Regulator. Nutrients. 2025;17(13):2206. doi:10.3390/nu17132206.