Function of thiamin  in the body

Metabolism
Thiamin is part of an enzyme system known as thiamin pyrophosphate which is essential for nearly every cellular reaction in the body. 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.

Brain and nerve function
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.

Absorption and metabolism
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.

Raw freshwater fish and shellfish contain an enzyme which breaks down thiamin. This can happen during food storage and preparation or as food passes through the gut. Thus large intakes of raw fish and shellfish can increase the risk of thiamin deficiency. Drinking large quantities of tea and coffee may reduce thiamin absorption.

Deficiency
Thiamin deficiency is rare in developed countries as refined flours and cereals are often fortified with this vitamin. However, deficiency symptoms are still seen in parts of the world where white rice makes up a major part of the daily diet.

Those at greatest risk of deficiency include some young children and teenagers, stressed adults, those who exercise very heavily, alcoholics, pregnant women, those on fad diets and people suffering from malabsorption diseases. Marginal deficiencies without clinical symptoms may be quite common among these groups. Elderly people are also at risk of thiamin deficiency and this may lead to reduced mental functioning, depression, weakness, suppressed immunity and gastrointestinal problems. Early thiamin deficiency may be easily overlooked as the symptoms are generalized and can include fatigue, depression and stress- induced headaches. There is some evidence to suggest that recurring mouth ulcers are due to thiamin deficiency.

Thiamin deficiency affects every cell in the body. Deficiency symptoms may be due to the interference of nerve functions dependent on thiamin and the build-up of toxic compounds as carbohydrates are incompletely metabolized. Factors which increase the demand for the conversion of carbohydrate to energy; for example, exercise, alcohol and sugary foods; may aggravate thiamin deficiency. Severe thiamin deficiency causes beriberi. Beriberi can affect the cardiovascular system (wet beriberi) and the nervous system (dry beriberi).

Brain and nervous system
One of the earliest signs of thiamin deficiency is reduced stamina. Depression, irritability and reduced ability to concentrate are later followed by fatigue, muscle cramps and various pains. Dry beriberi symptoms include numbness and tingling in the toes and feet, stiffness of the ankles, cramping pains in the legs, difficulty walking, and finally, paralysis of the legs with wasting of the muscles. Permanent damage to the nervous system can occur if the deficiency is not corrected in time. Thiamin deficiency may also be associated with reduced tolerance to pain.

Gastrointestinal system
Thiamin deficiency can also lead to nausea, lack of appetite, weight loss and constipation. Carbohydrate digestion and the metabolism of glucose are diminished.

Cardiovascular system
In the advanced stages of thiamin deficiency, the symptoms of wet beriberi include heart enlargement. Symptoms of cardiac failure such as breathlessness, ankle swelling and fatigue may follow. Marginal thiamin deficiency may contribute to heart disease.

Alcoholics
Alcoholics and binge drinkers are especially prone to thiamin deficiency as alcohol reduces absorption, alters metabolism and depletes body stores. Alcoholics also tend to have poor diets. Thiamin deficiency is associated with some of the symptoms of alcoholism such as mental confusion, visual disturbances and staggering gait. If thiamin deficiency is not corrected, permanent brain damage may result. This condition is known as Wernicke Korsakoff syndrome and is usually seen in people who have been addicted to alcohol for many years.

Sources
Good natural sources of thiamin include brewer's yeast, organ meats, wheatgerm, 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.

RDAs for thiamin in  USA
Men 1.2 mg

Women 1.1 mg

Pregnancy 1.4 mg

Lactation 1.5 mg
 
 

Women who are carrying or breastfeeding more than one baby would have a greater thiamin requirement.

Supplements

Thiamin supplements may be useful during times of stress, fever, diarrhea and during and after surgery. Many experts recommend 100 mg of thiamin per day for those who drink alcohol.

Toxic effects of excess intake
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 5 mg, but many people can tolerate much larger doses.

Therapeutic uses of supplements
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.

Elderly people
The results of a trial reported in the American Journal of Clinical Nutrition in 1997 suggest that thiamin supplements may help to improve quality of life in many elderly people. Researchers from hospitals in Christchurch, New Zealand measured red blood cell concentrations of thiamin pyrophosphate (TPP) in 222 people aged over 65 years. This measurement was done twice in three months. Thirty-five people had low levels at both measurement times. These people were divided into two groups and were given either a thiamin supplement of 10 mg per day or a placebo for three months. The researchers then assessed blood pressure, body weight, height, body mass index, hand grip strength and cognitive function in the subjects. The results showed that the supplements decreased blood pressure and weight and improved quality of life. There was a trend towards improved sleep and energy.

Fatigue
Like the other B vitamins, thiamin is used to treat fatigue. High-dose thiamin supplementation may be helpful in preventing or accelerating recovery from exercise-induced fatigue. In a small Japanese study done in 1996, the effects of 100 mg per day of thiamin was assessed in 16 male athletes. The athletes exercised on bicycles and changes in blood, heart and lung functioning were measured. In the thiamin supplement group, changes in blood glucose were suppressed and the athletes felt less fatigued.

Mental function
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.

Alcohol and drugs
Thiamin has been used to treat some of the symptoms of alcohol abuse, such as the reduction in brain chemicals associated with memory and thought processes.

In a study done in the US in 1997, thiamin supplements improved memory in cocaine-dependent patients. The patients were not taking cocaine during the study and were given 5 g of thiamin or a placebo. They were then asked to perform memory scanning tasks. The results showed that the patients taking the thiamin supplements performed significantly better than those taking the placebo.

Alzheimer's disease

Thiamin metabolism appears to be altered in Alzheimer's with lower levels of thiamin and enzymes which metabolize thiamin found in the brains of Alzheimer's disease patients. Clinical data suggest that high dose thiamin may have a mild beneficial effect in some patients with Alzheimer's disease but it does not appear to halt the progress of the disease.6
 

Interactions with other nutrients
Magnesium is necessary for the conversion of thiamin to its active form. Vitamin C helps improve thiamin absorption.

Interactions with drugs

Alcohol reduces thiamin absorption and conversion to the biologically active form. Digoxin, indomethacin, anticonvulsants, antacids and some diuretics may lead to the risk of deficiency. Smoking, caffeine, sulfa drugs and estrogen may also raise thiamin requirements.