An optimum intake of micronutrients and metabolites, which varies with age and genetic constitution, would tune up metabolism and give a marked increase in health, particularly for the poor and elderly, at little cost. 1) DNA damage. Inadequate intake of folic acid causes millions of uracils to be incorporated into the DNA of each cell with associated chromosome breaks, essentially producing a radiation mimic. Deficiencies of the metabolically connected vitamins B-6 and B-12, which are also widespread, also cause uracil incorporation and chromosome breaks. Inadequate iron intake (2 billion women in the world; 25% of U.S. menstruating women) causes oxidants to leak from mitochondria and damages mitochondria and mitochondrial DNA. Inadequate zinc intake (approximately 10% in the U.S.) causes oxidation and DNA damage in human cells. 2) The K(m) concept. Approximately 50 different human genetic diseases that are due to a poorer binding affinity (K(m)) of the mutant enzyme for its coenzyme can be remedied by feeding high-dose B vitamins, which raise levels of the corresponding coenzyme. Many polymorphisms also result in a lowered affinity of enzyme for coenzyme. 3) Mitochondrial oxidative decay with age. This decay, which is a major contributor to aging, can be ameliorated by feeding old rats the normal mitochondrial metabolites acetyl carnitine and lipoic acid at high levels. They restore the K(m) for acetyl carnitine transferase and the velocity of the reaction as well as mitochondrial function; reduce levels of oxidants, neuron RNA oxidation and mutagenic aldehydes; and increase old-rat ambulatory activity and cognition.