The three thiamin requirements of the rat.

Some nutrients are necessary parts of several different biochemical systems and are required for several different and measurable physiological functions. There are three measurable dietary requirements for thiamin in the rat. The largest is correlated with food intake and body weight gain data. A half-maximum response is produced by 7 micrograms of thiamin per day, and a maximum response is produced by a dose 2- to 4-times larger. The next requirement, showing a half-response at 1 microgram thiamin, relates to cardiovascular function. It is measured by the enlargement of the heart or by the rat bradycardia bioassay method for thiamin. The smallest requirement, occurring at 0.01 microgram thiamin, is associated with the nervous system responses characteristic of thiamin deficiency, and may be related to a variability in oxidative metabolism.