Thiamine, a coenzyme, was originally named vitamin B1. It is partially de-stroyed by heat and alkalies, and it is lost in cooking water.
Functions.Thiamine is essential for the metabolism of carbohydrates andsome amino acids. It is also essential to nerve and muscle action. It is absorbed in the small intestine.
Sources.Thiamine is found in many foods, but generally in small quantities.(See Appendix D.) Some of the best natural food sources of thiamine are unrefined and enriched cereals, whole grains, lean pork, liver, seeds, nuts, and legumes.
Requirements.Thiamine is measured in milligrams. The daily thia-mine requirement for the average adult female is 1.1 mg a day, and for the average adult male it is 1.2 mg a day. The requirement is not thought to increase with age. In general, however, an increase in calories increases the need for thiamine.
Most breads and cereals in the United States are enriched with thiamine, so that the majority of people can and do easily fulfill their recommended intake.
Deficiency.Symptoms of thiamine deficiency include loss of appetite,fatigue, nervous irritability, and constipation. An extreme deficiency causes beriberi. Its deficiency is rare, however, occurring mainly among alcoholics whose diets include reduced amounts of thiamine while their requirements are increased and their absorption is decreased. Others at risk include renal clients undergoing long-term dialysis, clients undergoing bypass surgery for weight loss, and those who eat primarily rice.
Because some raw fish contain thiaminase, an enzyme that inhibits the normal action of thiamine, frequent consumption of large amounts of raw fish could cause thiamine deficiency. Eating raw fish is not recommended. Cooking inactivates this enzyme.
There are no known ill effects from excessive oral intake of thiamine, but it may be toxic if excessive amounts are given intravenously.