1.6.1 Thiamin (or thiamine, also known as vitamin B1 )
The deficiency disease beriberi has been known for thousands of years. The name literally means ‘I can't, I can't’ in Sinhalese (a major language in Sri Lanka), and reflects the crippling effect on its victims, who suffer from neurological symptoms, including pain, fatigue and paralysis, and cardiovascular disease. The disease was most common in southeast Asia, where white or ‘polished’ rice was a major part of the diet. The main source of thiamin is in the outer layers of the grain, the bran, which is removed during milling to produce white rice grain and white rice flour. Thiamin is added to white flour in the UK and many breakfast cereals are also enriched in thiamin. It is present in seeds, nuts and in beans and in smaller quantities in other foods such as meat, milk and potatoes. Since potatoes are eaten frequently in the UK diet, they can form a useful source, though thiamin is gradually destroyed by boiling water and it is estimated that 20% of the possible dietary intake is lost in cooking.
Thiamin is essential in many of the metabolic pathways in the body, especially in the processing of carbohydrate to provide energy. Since the nervous system relies almost exclusively on carbohydrate (glucose) for its energy, it is not surprising that the symptoms of deficiency are seen there. Because, as a water-soluble vitamin, little thiamin can be stored in the body, symptoms appear in less than a month on a diet in which it is completely absent. The early symptoms can, however, be rapidly corrected by regular intake of thiamin.
There are two forms of beriberi, known as the ‘wet’ and ‘dry’ forms. In ‘wet’ beriberi, there is swelling of the limbs, increased heart rate, lung congestion and an enlarged heart, all symptoms of heart failure, which can ultimately be fatal. The symptoms of ‘dry’ beriberi include pain, tingling and loss of sensation in the hands and feet, muscle wasting and gradual loss of function and paralysis of the legs, brain damage and eventually death. Nowadays, with better nutritional information and the addition of thiamin to many foods, beriberi is rarely seen, except in people with alcoholism, who mainly have the ‘dry’ form, in a condition called Wernicke-Korsakoff syndrome. Chronic alcoholism is often associated with poor nutrition and therefore a low intake of thiamin. Additionally, alcohol appears to interfere with thiamin absorption from the gut. The symptoms of Wernicke-Korsakoff syndrome begin with peripheral nerve damage (loss of feeling in hands and feet), then damage to the central nervous system and finally a confused mental state, or psychosis, which affects mood, language and thinking.
Because of its involvement in carbohydrate metabolism, additional thiamin may be needed during pregnancy, lactation and also in cancer patients and in people on kidney dialysis. It has been suggested that additional thiamin could be beneficial to performance in certain sports, but experiments so far have produced no evidence to support this idea.