Thiamin, which is also known as vitamin B1, was the first B vitamin to be discovered. It is involved in energy production and carbohydrate and fatty acid metabolism. It is vital for normal development, growth, reproduction, healthy skin and hair, blood production and immune function. Thiamin is also necessary for the metabolism of alcohol. Outright deficiencies are rare in developed countries.
Thiamin is particularly important for the normal functioning of nerves. It is necessary for the synthesis of acetylcholine, a neurotransmitter which affects several brain functions including memory, and also maintains muscle tone of the stomach, intestines and heart. Digestive diseases such as colitis, diverticulosis, celiac disease and chronic diarrhea reduce thiamin absorption as do protein and folate deficiencies. Some thiamin is stored in the heart, liver and kidneys but these stores do not last long and a continuous intake is necessary to prevent deficiency.
Good natural sources of thiamin include brewer’s yeast, organ meats, wheat germ, oatmeal, whole grains, pork, fish, poultry, nuts, dried beans and peas, avocado, vegetables such as spinach and cauliflower, and thiamin-enriched flours and cereals.
Thiamin is found in the germ and bran of wheat and in the outer covering of rice grains, so refining grains removes much of the thiamin. The vitamin is easily destroyed by cooking heat and is lost in the water used to cook food. It is also destroyed when food becomes alkaline, thus adding bicarbonate of soda to thiamin-rich foods causes losses. Sulfite food additives also destroy thiamin.
Toxicity is very rare as excess thiamin is excreted in the urine. Long-term excessive use can produce symptoms of hyperthyroidism: headache, irritability, trembling, rapid pulse and insomnia. With injected thiamin, reactions of itching, weakness, gastrointestinal bleeding, low blood pressure, pain, sweating, nausea, tingling and faintness can sometimes occur. The lowest daily dose known to cause side effects is 5mg, but many people can tolerate much larger doses.
Thiamin supplements are used to prevent and correct the heart and nerve problems caused by thiamin deficiency. Thiamin also has a mild diuretic effect and may be beneficial to heart function. Restoring normal thiamin levels in diabetics who are deficient leads to improvements in blood sugar metabolism.
Thiamin supplements have been shown to improve mood and mental function, possibly via effects on the neurotransmitter, acetylcholine. Thiamin supplements also appear to improve mental function in epileptics treated with the anticonvulsant drug, phenytoin.
Thiamin supplements have been used to treat other problems that affect the nerves, including multiple sclerosis, Bell’s palsy, neuritis and diabetic neuropathy. As with the other B vitamins, thiamin is used to relieve stress and muscle tension and to speed healing after surgery. Some people use thiamin supplements in doses of up to 100mg to help repel mosquitoes and other biting insects, and it may take several weeks of supplement use before beneficial effects appear.
Magnesium is necessary for the conversion of thiamin to its active form. Vitamin C helps improve thiamin absorption.