Vitamin B1 (thiamin)
Thiamin is an essential micronutrient for human and animal life.
Because the human body cannot produce thiamin, its supply depends almost completely on dietary intake. Thiamin is a key factor in carbohydrate and branched-chain amino acid, and lipid metabolism. Date of preparation: December 2018
Contribution:
Importance of thiamin for health
Thiamin is an essential micronutrient for human and animal life. Since the human body cannot produce thiamin, its supply depends almost completely on dietary intake (1, 2). Given the short half-life of this vitamin, body stores are limited and require a regular supply to maintain tissue thiamin levels. Thiamin diphosphate (TPD), also called thiamin pyrophosphate (TPP), is the coenzymatic form of vitamin B1 and constitutes about 80% of total body thiamine. It is a key factor in carbohydrate and branched-chain amino acid, and lipid metabolism (1, 3). Its synthesis from free thiamin requires magnesium, adenosine triphosphate (ATP), and the enzyme thiamin pyrophosphokinase (TPK) (4).
Thiamin absorption in the human body occurs after de-phosphorylation to free thiamin, in the intestinal lumen through a pH- and Na+-dependent carrier mediated system, while thiamin transporters THTR1 and THTR2 support the uptake in the intestinal epithelium cells (5). Free thiamin is then transported to the cells, where phosphorylation to TDP occurs by thiamine pyrophosphokinase-1 (TPK-1). There is no known intracellular role for TMP (6).
Sources of thiamin
Whole grains, meat, and fish are good food source of vitamin B1, while dairy products and most fruits are low in thiamin. Some studies have shown increased thiamin adsorption with low intake, but data on thiamin bioavailability from foods are sparse. Food processing such as heating, pasteurization, or cooking in water can noticeably reduce thiamin levels in the foods. White rice -without thiamin enrichment- only contains 1/10 of the thiamin available in unenriched brown rice (4).
Risks of deficiency
Inadequate intake can lead to thiamin deficiency; however, lower absorption or higher excretion than normal, or consumption of anti-thiamin factors in food can also cause thiamin insufficiency. Other thiamin affecting conditions include alcohol dependence, HIV/AIDS status, or the use of some medication (4).
Increased thiamin requirements are commonly due to strenuous exertion, fever, pregnancy, breastfeeding, and adolescent growth, which increases the risk of deficiency in settings of marginal thiamin intake (3, 4).
Thiamin is a key factor for enzymes involved in glucose metabolism; thus, conditions of increased glucose demands such as Malaria, or providing carbohydrates to severely starved individuals can lead to a higher demand for thiamin in glycolysis and the citric acid cycle that precipitates thiamin deficiency (4, 7).
Beriberi is the main thiamin deficiency syndrome, caused by severe thiamin deficiency, and can be sub-divided into categories as outlined below:
Table 1: Beriberi sub-categories (1, 4, 7)
| Deficency | Effect |
|---|
|
Dry beriberi
|
Neuropathy, "burning feet syndrome"
Exaggerated reflexes
Diminished sensation and weakness of arms and legs
Muscle pain and tenderness
|
|
Wet beriberi
|
Neurologic symptoms Rapid heartbead, oedema, difficulty breathing, congestive heart faliure
|
|
Cerebal beriberi
|
Wernicke's encephalopathy
Korsakoff's psychosis
|
|
Gastrointestinal beriberi
|
Decreased activity of thiamin-dependent enxymes cause accumilation of pyruvate and lactate. Symptoms: Nausea, vomiting, abdominal pain.
|
Note: Wernicke’s encephalopathyis a result of wet berberi and its diagnosis is based on a “triad” of signs including abnormal eye movements, stance and gait ataxia, and cognitive impairments. Without treatment, irreversible neurologic damage can lead to further clinical manifestations, known as Korsakoff’s psychosis, which involves a confused, apathetic state and a profound memory disorder, with severe amnesia and loss of recent and working memory. Thiamin deficiency which affects the central nervous system is also known as Wernicke-Korsakoff syndrome(WKS), when an individual presents with the amnesic state along with eye-movement and gait disorders (7).
Risks of excess
Excess thiamin is excreted in the urine. No upper intake levels have been established given to the lack of reports of adverse effects due to excess thiamin intake. The short half-life of thiamin may contribute to the lack of toxicity, and the Food and Nutrition Board notes that high thiamin intake levels could have adverse effects (4, 7).