Integrated saturation model for tissue micronutrient concentrations applied to liver folacin.

A mathematical model for tissue micronutrient concentration as a function of dietary nutrient concentration, time, and growth rate is derived from assumptions of saturable nutrient storage capacity and reversible storage and depletion processes. The model is tested using liver folacin concentration data from rats. The estimated maximum liver concentration (16.8 micrograms/g), and half-life (8 days) of liver folacin are compared to more direct observations in the literature. The intake producing the half-maximal liver folacin concentration (1.3 mg folic acid/kg diet) compares well to the 1978 NRC recommendation for the rat. The estimated model parameters obtained from animals at two to three months of age are used successfully to predict additional observations from younger, more rapidly growing animals. The model has potential application in predicting the effects of food enrichment or therapeutic nutrient supplementation programs, and in the development of bioassay methods and recommended intakes.