Thiamin (a.k.a. vitamin B1 a.k.a. aneurin) is a water-soluble vitamin that is an essential component in amino acid and carbohydrate metabolism. It is one of the fundamental components involved in the production of the body’s energy.

      The daily requirement of thiamin is a function of metabolic rate. While extremely active individuals can expect to have a slightly higher requirement of the vitamin, the gender differences reflected in the table below are generally assumed to be related to body size and energy utilization.
      Figures for the recent National Academy of Sciences Dietary Reference Intakes study are based upon slightly different age ranges, which accounts for the overlapping age groups.

      The primary dietary sources of thiamin are a combination of natural and fortified food products. These include breads, wheat germ, whole and enriched grains (primarily cereals), pastas, rice, pork, meat substitutes, beans, seeds and nuts.

      Initially, thiamin deficiency is manifested as a general loss of energy, but can lead to loss of appetite, pain in the extremities, muscular weakness and even central nervous system damage if not corrected. Severe deficiency can lead to a disease known as beriberi, and ultimately result in paralysis or heart failure.
      Although the vitamin requires frequent replenishment, dietary deficiencies are uncommon in the developed world. The most common cause of thiamin deficiency are intestinal disorders causing malabsorption, and the so-called Wernicke-Korsakoff syndrome resulting from chronic alcoholism.

      Thiamin supplements, typically as part of a multivitamin, make sense for individuals who have poor diets, whether due to poor socio-economic conditions or neglect resulting from a fast-paced lifestyle. A typical multivitamin contains 1.5mg of thiamin, which is 100% of the current Reference Daily Intake (RDI).

      Although severe reactions have been recorded for massive doses of thiamin, these appear to be rare and associated with direct administration in a clinical setting (such as an injection), not from dietary or supplemental sources.
      The reason for an apparent absence of a health risk from dietary sources alone is an increasingly lower absorption and higher urinary excretion rate of the vitamin as doses are increased. In other words, most of what is consumed in high dose supplements passes right through the body.
      The recent National Academy of Sciences Dietary Reference Intakes study does not set a Tolerable Upper Intake Levels (UL) for thiamin due to a lack of adequate research. Their report does indicate, however, a so-called “exposure assessment” (an apparently unremarkable intake level) of approximately 10mg/day from both dietary and supplemental sources, based upon the highest mean thiamin intake reported among adults of mixed age and gender.