Thiamin is a water-soluble vitamin from the B complex group of nutrients. It is occasionally referred to as aneurine (indicating a link with nerves), particularly in the USA. It is similar in function to riboflavin (B2) and niacin, two other B complex nutrients that are also involved in converting the food we eat into energy.

Thiamin is best known for its beneficial effect on the nervous system and on mental stability. It is also known for the severity of its deficiency symptoms which, at worst, can result in death. Thiamin was the first vitamin for which a precise activity in the body was defined in biochemical terms, which is why it was the first B vitamin to be classified. This took place at Oxford between 1928 and 1935.

All animal and plant foods contain some thiamin, but content varies widely among different foods.

Richest sources are:

  • unpolished (unprocessed) natural brown rice 
  • yeast extract

Other good food sources are: 

  • liver, kidney and pork 
  • fatty fish
  • wholemeal bread, wheat bran and wheatgerm 
  • oat flakes, maize, soya
  • beans, peas, lentils 
  • potatoes

There are lesser amounts to be found in:

  • other meat – beef, lamb and chicken 
  • white fish
  • dairy produce
  • root vegetables 
  • citrus fruits

In most people thiamin is rapidly absorbed from the small intestine. It then circulates in the blood system to the liver, kidney, head and brain. Before it can be used, thiamin is converted into an active form, a co-enzyme. This process, known as phosphorylation, takes place in body tissue but mostly in the liver cells. Since it is water-soluble, thiamin is not stored in the body but needs to be obtained from dietary sources on a daily basis. It is, however, retained for a short time in some organs in trace amounts.

Thiamin is the most unstable of the B complex nutrients. All methods of cooking and processing either destroy or reduce levels of thiamin but by far the greatest loss is due to thiamin’s water solubility. 

Some vitamin content can be regained by using cooking water in gravy or sauces, but little is gained in this way. When frozen meat thaws, thiamin is lost in the water and blood. Even cooking methods such as light braising or steaming can cause up to 25 per cent thiamin loss from vegetables. Eating excessive amounts of simple carbohydrates (foods high in refined flour and sugar) will cause thiamin depletion, as will smoking, alcohol, oestrogen drugs (contraceptives or hormone pills) and antacid tablets.

Early symptoms of deficiency include fatigue, weight loss and anorexia. In later stages, sufferers can experience constant tiredness, irritability and insomnia. If the deficiency is not treated, more serious symptoms develop including impaired memory and concentration and emotional instability, such as overreacting to normal stresses and strains and feelings of inadequacy. Constipation, accompanied by vague abdominal and chest pains may occur. Eventually nervous symptoms could worsen and tingling, burning sensations may occur in the feet with some calf tenderness.

These symptoms of deficiency are recorded from healthy individuals who withheld thiamin from their diet deliberately to find out how it affected the nervous system. The earliest sign was nausea between days 3 and 7 after starting the controlled exclusion diet.

Effects on the brain and nervous system and personality changes started before there were any obvious physical changes. This means that thiamin deficiency can be a disturbing state and one that is easily misdiagnosed.

The water-soluble vitamin C (also stress related) is compatible with thiamin.

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