Know Your Nutrients—Thiamine (B1)

Thiamine (also thiamin or vitamin B1) is part of the B complex vitamins. It was the very first compound identified as a vitamin, and thus retains its historical numerical place as first in the B vitamin family.

Dietary thiamine occurs in two forms: the free form that is found in plant products and the phosphorylated form found in animal products. Only free thiamine can be absorbed by the body. When the phosphorylated form is ingested, it can be acted upon by enzymes in the small intestine to free the thiamine from the phosphate group. Thiamine is primarily absorbed in the upper jejunum, with some uptake in the duodenum and ileum. Uptake occurs primarily via active absorption when intake is less than 5mg per day. At higher concentrations, passive diffusion increases as a percent of absorption.

As a water-soluble vitamin, thiamine is poorly stored in the body, thus depletion can occur rapidly if the supply is not continuously replenished via diet or supplements.

Once absorbed into the body, thiamine is converted into thiamine pyrophosphate (TPP), thiamine monophosphate (TMP), and thiamine triphosphate (TTP). This process is magnesium-dependent; thus, magnesium deficiency can contribute to the development of thiamine deficiency by reducing the amount of active thiamine available. Thiamine pyrophosphate (TPP) is considered to be the most important form of thiamine. TPP is a cofactor for several mitochondrial enzymes that contribute to the formation of acetyl-co A and succinyl-co A. Ultimately, this is a critical step in the production of energy from food. TPP also acts as a coenzyme to transketolase, which catalyzes the synthesis of the energy molecules ATP and GTP, the nucleic acids deoxyribonucleic acid (DNA), ribonucleic acid (RNA), and other enzymes. TPP also appears to have a direct role in nerve conduction and muscle contraction, which would help to explain the potentially severe neurological symptoms that can occur in deficiency.


Thiamine has many important functions in the body but is especially critical for energy production and nerve transmission. For this reason, beriberi, a disease caused by a deficiency of thiamine, reflects problems related to bodily systems with high-energy needs, such as the heart and brain, as well as nerve function. There are three classes of beriberi: dry, wet, and cerebral (Wernicke-Korsakoff syndrome). Very mild thiamine deficiency presents with vague symptoms, such as fatigue, weakness, and difficulty concentrating. With dry beriberi (which is the most common form of beriberi), symptoms include vomiting, loss of appetite, weakness, sleepiness, burning feet, calf and leg pain, abdominal pain, constipation, headache, and cramping. Peripheral polyneuropathy is also common. The neuropathy associated with thiamine deficiency begins with fatigue and loss of sensation, pain, and “heaviness” in the legs. Then pretibial edema develops, along with glove-and-stocking paresthesias and difficulty with certain physical tasks, such as climbing stairs and standing on one leg.1 Burning pain, especially in the feet (although it can occur anywhere) is a hallmark symptom of severe thiamine deficiency. If there is involvement of the brain (cerebral beriberi), mental confusion may be a prominent symptom. While cerebral beriberi can be severe enough to include symptoms of delusion, hallucination, or psychosis, more mild symptoms are confabulation, memory impairment, eye dysfunction, such as double vision (due to optic neuropathy), inability to walk or stand, or waddling gait. Wet beriberi presents with symptoms of congestive heart failure.

Known risk factors for thiamine deficiency include poor dietary intake, weight-loss surgery, intestinal loss (primarily through vomiting), alcohol intake, eating disorders, and dialysis.

Recommended Intake

The recommended dietary intake (RDI) of thiamine for adults is 1.2mg/day for men, 1.1 mg/day for women, and, in children, 0.2mg/day during early infancy steadily increasing with age. Pregnant women should increase their daily intake of thiamine to 1.4 mg/day. In food-secure countries with overall easy access to thiamine-rich foods, thiamine deficiency is rare in healthy people. However, in countries with poor food security in which the primary sources of dietary energy are derived from starchy, low-thiamine staples, such as processed white rice, thiamine deficiency is much more prevalent.1


Ingesting more thiamine than the RDI is considered safe. Most multivitamin formulations provide at least the daily value of thiamine. The Food and Nutrition Board of the Institute of Medicine has not set a tolerable upper level (UL) because no evidence of toxicity from oral ingestion of thiamine has been reported, even with doses as high as 200mg taken for long periods of time. Intravenous thiamine has been known to produce rare anaphylactic reactions.

Dietary Sources

Thiamine is found naturally in meats (pork is a good source), fish, legumes, nuts, and whole grains. However, fortified grains are the richest and most common source of thiamine in most diets.

Anti-thiamine Factors

Some foods contain antithiamine factors (ATFs). ATFs act to oxidize dietary thiamine in the digestive system and render it inactive. ATFs are commonly found in coffee (including decaffeinated) and black tea. Some polyphenols, such as those in blueberries and the cabbage family, may also act as ATFs. Raw or fermented fish contains the enzyme thiaminase, which destroys thiamine. This is not a concern in cooked fish, since heat inactivates this enzyme. Additionally, chlorine compounds that may be found in drinking water can destroy thiamine with prolonged contact. For example, rice cooked in chlorinated water may have one-third less thiamine than rice cooked in filtered or distilled water.3

Drug Interactions

There are some known drug interactions with thiamine. Loop diuretics, such as furosemide (Lasix®), increase urinary excretion of thiamine, and phenytoin (Dilantin®) appears to disrupt thiamine metabolism, resulting in low levels, as does the chemotherapeutic agent, 5-fluroucil. Oral contraceptives and antacids may also alter thiamine status, although the implications with these drugs are not well understood. As mentioned earlier, thiamine interacts with magnesium, as well as other nutrients, including B6, B12, and folate; thus, a deficiency in these nutrients can affect thiamine levels in the body.

Editor’s Note

Please consult with your physician or a certified dietitian/nutritionist to determine a diet that is best suited to your individual needs.

This article was adapted with permission from Jacques J. Vitamin B1 (thiamine). Micronutrition For The Weight Loss Surgery Patient. Edgemont, PA: Matrix Medical Communications; 2005:

Other Sources

1. Sewell AR, Recht, LD. Nutritional neuropathy, Access 25 May 2005

2. National Institute of Health website. Thiamin. Accessed 17 Mar 2023.

3.. Yagi N, Itokawa Y. Cleavage of thiamine by chlorine in tap water. J Nutr Sci Vitaminol. (Tokyo) 1979;25(4):281–7.

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