It is a group of substances (the vitamin B complex) that are essential for the working of certain enzymes in the body and, are generally found together in the same foods. They include thiamine (vitamin B1), riboflavin (vitamin B2), pyridoxine (vitamin B6), and cyanocobalamin (vitamin B12). B vitamins are a class of water-soluble vitamins that play important roles in cell metabolism and synthesis of red blood cells. Though these vitamins share similar names, they are chemically distinct compounds that often coexist in the same foods.
Thiamine (vitamin B1) is a water-soluble vitamin. It is essential for the utilization of carbohydrates. Thiamine pyrophosphate (TPP), the coenzyme of carboxylase plays a part in activating transketolase, an enzyme involved in the direct oxidative pathway for glucose. In thiamine deficiency, there is an accumulation of pyruvic and lactic acids in the tissues and body fluids. Thiamine pyrophosphate, the active form of thiamine, is an important cofactor in the citric acid cycle that is active in the heart and brain. The vitamin is also involved in nucleic acid and fatty acid synthesis.
Thiamine occurs in all-natural foods, although in small amounts. Important sources are: whole-grain cereals wheat, gram, yeast, pulses, oilseeds, and nuts, especially groundnut, Meat, fish, eggs, vegetables, and fruits contain smaller amounts. Milk is an important source of thiamine for infants, provided the thiamine status of their mothers is satisfactory.
Thiamine is readily lost from rice during the process of milling. Being a water-soluble vitamin, further losses take place during the washing and cooking of rice. This is the basis for advising people to eschew highly polished rice and eat parboiled or under-milled rice. Much of the thiamine in fruits and vegetables is generally lost during prolonged storage. Thiamine is also destroyed in toast and in cereals cooked with baking soda. The occurrence or absence of beriberi is determined by the local customs and cultural practices concerning the processing and cooking of rice and other foodstuffs.
Recommended daily allowance is 0.4 mg/1000 Cal of carbohydrate intake. If more than this is given it is merely lost in the urine. Patients on regular hemodialysis should routinely be given supplements of thiamine. Thiamine should also be given prophylactically to people with persistent vomiting or prolonged gastric aspiration and those who go on long fasts.
Deficiency:
The two principal deficiency diseases are beriberi and Wernicke's encephalopathy. Beriberi may occur in three main forms:
(a) The dry form characterized by nerve involvement (peripheral neuritis)
(b) The wet form is characterized by heart involvement (cardiac beriberi)
(c) Infantile beriberi, seen in infants between 2 and 4 months of age. The affected baby is usually breast-fed by a thiamine-deficient mother who commonly shows signs of peripheral neuropathy. Wernicke's encephalopathy (seen often in alcoholics) is characterized by ophthalmoplegia, polyneuritis, ataxia, and mental deterioration. It occurs occasionally in people who fast. The clinical picture is dominated by cardiomegaly, cyanosis, and dyspnea. The disease may result in death after a few weeks, in the infantile form. Wernicke encephalopathy may occur in thiamine deficient infants and children and consists of a triad of mental confusion, ocular abnormalities (ophthalmoplegia and nystagmus), and ataxia. Hemorrhagic lesions may be seen in the thalamus and periventricular gray matter.
Thiamine deficiency may be suspected in all cases of malnutrition. The diagnosis is confirmed by measurement of 24 hours urinary thiamine excretion, which in children is 40-100 μg/ day; values below 15 μg/day are deficient. Diagnosis of deficiency can also be based on the response of red cell transketolase to the addition of thiamine in vitro. Erythrocytes from deficient persons have a greater response to the addition of thiamine pyrophosphate than normal controls. An increase in transketolase activity of less than 15% is normal, 15-25% mild deficiency, and over 25% severely deficient. Serum lactate and pyruvate levels may be raised.
Treatment with thiamine leads to resolution of neurologic and cardiac symptoms within 24-48 hours. Treatment of patients with mild beriberi with thiamine (5 mg/ day) is satisfactory. Severely ill children should receive 10 mg intravenously twice daily. In the management of fulminant heart disease, higher doses of thiamine with the treatment of congestive heart failure are necessary.
Beriberi can be eliminated by educating people to eat well-balanced, mixed diets containing thiamine-rich foods (e.g., parboiled and under milled rice) and to stop all alcohol. Direct supplementation of high-risk groups (e.g. lactating mothers) is another approach. Beriberi tends to disappear as economic conditions improve and diets become more varied. The disease, as has been shown, is not completely vanquished but the knowledge and resources needed to bring about its disappearance are available.
