Water and aging

Having evolved from the sea and developed from an embryo, the species and the individual lose water--the medium and solvent wherein these processes occur--continually as they age. From an embryo, which is about 90% water, to a senescent individual in the tenth decade, there is a decline in body water to 60% or below. This loss in body water has profound effects on pathophysiology, making older persons susceptible to both under- and overhydration because they have a smaller volume of distribution for exogenous water. A colloid osmotic macromolecular aggregation model has been hypothesized to explain water loss in aging individuals.