Thiamine is a white crystalline substance, readily soluble in water but not in fat or fat solvents. It is rapidly destroyed by heat in neutral or alkaline solutions. However, in acid solutions it is heat resistant.
Thiamine is concerned with a stage in the breakdown of carbohydrates, which explains how signs of efficiency develop most rapidly when diets rich in carbohydrates are eaten.
The total amount of thiamine in the well nourished human body is small, about 2.5 mg. The highest concentration is found in the heart, brain, liver, kidneys and skeletal muscles. The body has no means of storing any excess, so that no benefit derives from taking mega doses as the excess is passed in the urine.
Symptoms usually include loss of appetite (anorexia) and mental changes resembling anxiety states, with irritability and easy exhaustion. Dietary deficiency of thiamine becomes important when it is sufficiently severe to cause a biochemical lesion interfering with the normal metabolism of CHO. The resultant disease state is called Beriberi.
All animal and plant tissues contain thiamine and it is therefore present in all whole unprocessed natural foods. The richest sources are wholegrain cereals, nuts, peas, beans and other pulses and yeast.
All green vegetables, roots, fruits, flesh foods and dairy products (except butter) are good sources. In the refining of sugar and cereal products all the natural thiamine may be removed.
As thiamine is readily soluble in water, considerable amounts may be lost when vegetables are cooked in excess water. It is relatively stable to temperatures up to boiling point, provided that the medium is slightly acid. But if baking powder or soda is added almost all the vitamin is destroyed.
Recommended Minimum Dietary Intakes
The requirement for thiamine relates to the amount of energy, especially CHO consumed.