Water balance throughout the adult life span in a German population

Mild dehydration, defined as a 1–2 % loss in body mass caused by fluid deficit, is associated with risks of functional impairments and chronic diseases. Whether water requirements change with increasing age remains unclear. Therefore, the aim of the present investigation is to quantify hydration status and its complex determining factors from young to old adulthood to analyse age-related alterations and to provide a reliable database for the derivation of dietary recommendations. Urine samples collected over a 24 h period and dietary records from 1528 German adults (18–88 years; sub-sample of the first National Food Consumption Survey) were used to calculate water intake (beverages, food and metabolic water) and water excretion parameters (non-renal water losses (NRWL), urine volume, obligatory urine volume) and to estimate hydration status (free-water-reserve) and ‘adequate intake (AI)’. Median total water intake (2483 and 2054 ml/d, for men and women, respectively (P