Role of Thiamine
Thiamin is necessary for the metabolism of carbohydrates and amino acids to adenosine triphosphate (ATP), the primary source of energy in the human body. Thiamin is found in good amounts in milk, lean pork, legumes, rice bran, and the germ of cereal grains, but is lost during food processing and cooking. The current recommended daily allowance (RDA) for thiamine by government advisory panels is about 1.5 mg.

Mental benefit of Thiamine
Studies indicate that supplementation with thiamine provides cognitive benefits. Dr. Benton and colleagues gave 50 mg of thiamin daily to young adult females for a period of two months. The women reported being more clearheaded, composed, and energetic. The taking of thiamin had no influence on memory but reaction times were faster following supplementation. Prior to taking the thiamin, the women had normal blood levels of this vitamin.

Researchers at Princess Margaret Hospital in Christchurch, New Zealand, measured thiamin levels in elderly individuals before giving them 10 mg of thiamine a day. Only the subjects with low thiamin concentrations showed benefits. They had an improvement in quality of life with more energy and deeper sleep, along with decreased blood pressure and weight.

Availability of Thiamine supplement
Thiamin is now sold in its coenzyme form called cocarboxylase or thiamin pyrophosphate (TPP). Human studies giving TPP to evaluate cognitive functioning have not yet been published. See also Benfotiamine.

Thiamine deficiency
A deficiency of thiamine causes tiredness and weakness. As the thiamine deficiency becomes worse, psychosis and nerve damage can occur. Thiamine deficiency in the United States occurs in those who abuse alcohol for several decades. Thiamine deficiency can lead to a disease called beriberi.

Thiamine deficiency in patients with diabetes
High prevalence of low plasma thiamine concentration in diabetes linked to a marker of vascular disease.
Diabetologia. 2007 Oct;50(10):2164-70. Department of Biological Sciences, University of Essex, Colchester, Essex, UK.
Diabetic patients (26 type 1 and 48 type 2) with and without microalbuminuria and 20 normal healthy control volunteers were recruited. Erythrocyte activity of transketolase, the concentrations of thiamine and related phosphorylated metabolites in plasma, erythrocytes and urine, and markers of metabolic control and vascular dysfunction were determined. Plasma thiamine concentration was decreased 76% in type 1 diabetic patients and 75% in type 2 diabetic patients. Low plasma thiamine concentration is prevalent in patients with type 1 and type 2 diabetes, associated with increased thiamine clearance.

Thiamine questions
Q. Is it true that thiamin vitamin B1, taken orally, prevents mosquitoes from biting?
   A. I have not seen good studies on this, but I have a friend who swears that taking a thiamin supplement by itself without the other B vitamins prevents mosquitoes from biting her. She takes 50 mg of thiamin, and she thinks that taking a B complex does not work, it has to be thiamin by itself.

Q. If I bought a bottle of thiamine Vitamin B1 water-soluble capsules; would be best to swallow the capsule whole with a glass of water or break the capsule open and put the thiamine powder in my mouth and then swallow this with a glass of water for better absorption? A lady friend is beginning The Thiamine Therapy as 500 mg. capsule daily; and my friend would like to know the answer to this question: my friend has advanced multiple sclerosis.
   A. Practically speaking it would not make much of a difference. Swallowing the thiamine capsule whole is just fine. We have not come across evidence that high dosages of thiamine are effective as a treatment for multiple sclerosis.

Q. I've read that thiamine has to be converted to cocarboxylase in the body. My question is would thiamine supplements already in the cocarboxylase form and sub-lingual (let's say 25 mg) be as effective as a much larger dose (maybe 100 mg or more) of Thiamine HCI (hydrochloride) in a capsule? Swallowing the cap would be subject to stomach acid, but sub-lingual would be absorbed directly into the bloodstream would it not?
   A. Yes, most likely the sublingual and cocarboxylase form would be more potent than thiamine hydrochloride in capsule form. However, as the benefits may perhaps be better, there is a potential that the side effects would be more pronounced. A high dose or quick absorption is not necessarily healthier. But each person and each medical condition being treated is different.