Vitamin B1 (Thiamine, Aneurine)

 Vitamin B₁ (Thiamine, Aneurine)

(Antineuritic factor, Antiberiberi substance)

Introduction

Beriberi, a disabling condition, was endemic for centuries in the Orient and Pacific islands and this was finally proved to be deficiency disease. An analogous condition was produced artificially in hens in 1890 when Eijkman found out that birds fed with polished rice developed polyneuritis. In 1911 Dr. Casimir Funk cured polyneuritis in birds by administering concentrate of rice polishing. In 1926 this vitamin in pure form was isolated by Jansen and Donath and in 1936 the vitamin was synthesized by Williams and his coworkers.

Chemistry

Free thiamine is a basic substance containing a pyrimidine and a thiazole ring. It is generally prepared as a thiamine hydrochloride. In yeast it is found combined with a pyrophosphate. It contains sulphur and a primary amino group.

Properties

·        white, crystalline substance

·        water soluble

·        destroyed by heat but can stand short boiling up to 100°C. Hence, it is only partly lost in cooking unless the pH is low

·        destroyed in canning processes, autoclave, long boiling or boiling with alkali

·        stable in acid medium

·        on oxidation it produces thiochrome which gives fluorescence

Distribution

Animal sources

·        Generally poor but egg-yolk contains fair amount (100 i.u.)

Plant sources

·        Cereals (in the husk and embryo)

·        pulses

·        nuts

·        non leafy vegetables, i.e., beets, carrots, turnips, lettuce, cauliflower, beans

·        Pears

Polished rice and white flour are poor in this vitamin content.

Absorption

Free thiamine is absorbed readily from the small intestine. It is not much stored in the body. About 25% of the ingested vitamin B₁ is excreted in the urine.

International unit

An international unit of thiamine is equal to 3 gm of thiamine hydrochloride.

Functions

(1) The pyrophosphate ester of thiamine is a coenzyme (co carboxylase) and being bound to a specific protein (apoenzyme) together with a-lipoic acid and Mg++ forms the active enzyme carboxylase, which is responsible for the oxidative decarboxylation of pyruvic acid, a-ketoglutaric acid and other keto acids. It is an essential step in the final oxidation of sugar in the tissues and brain.

(2) It also helps the enzyme system which is responsible for the synthesis of fats from carbohydrates and Thiamine pyrophosphate is also a coenzyme for the transketolase reaction in the phosphogluconate oxidative pathway of carbohydrate metabolism.

Deficiency signs

Its deficiency causes a disease named Beriberi which has three types as follows-

·        dry

·        wet

·        cardiac or mixed type

Dry beriberi is associated with disorders of the nervous system.

In wet beriberi, the polyneuritis is accompanied by edema.

Cardiac beriberi is associated with signs of congestive cardiac and circulatory failure.

The mixed type with any combinations of the above may also be found.

Daily requirement

It is about 18 mg for a diet producing 3,000 calories. The requirement is increased in pregnancy, lactation, heavy work, high carbohydrate diet, etc. Daily intake for children ranges from 0.4 mg for infants to 13 mg for pre-adolescents. Requirement of thiamine increases in shock, hemorrhage, serious illness, injury, during oral administration of antibiotics, etc.