Water balance throughout the adult life span in a German population

Abstract

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,0·0001)), decreased with increasing age only in males (P¼0·001). Obligatory urine volume increased in both sexes (P,0·0001) due to decreased renal concentration capacity. The latter was balanced by a decrease of NRWL (P,0·05), leaving the free-water-reserve and therefore hydration status almost unchanged. Calculated 'AI' of total water was the same for young (18 -24 years) and elderly ($65 years) adults (2910 and 2265 ml/d, for men and women, respectively). The present study is the first population-based examination showing that total water requirements do not change with age although ageing affects several parameters of water metabolism. Reduced sweat loss with increasing age appears to be primarily responsible for this observation.

Bad results obtained from the current public health policies and recommendations of hydration

“…This is in agreement with other studies evaluating fluid intake in other populations (30)(31)(32). However, in our study, the percentage of men who met the EFSA recommendations was similar to the percentage of women (63.3% of men, 62% of women).…”

Urinary hydration biomarkers and dietary intake in children

“…Compared to other biomarkers, FWR has the advantage of considering the maximum capacity of kidney concentration and, in addition, it takes into account a safety margin to ensure adequate hydration (9). The prevalence of inadequate hydration status is higher than the one reported by Manz in German children, although the mean 24 h urine osmolality (667 mOsm/kg in boys and 585 mOsm/kg in girls), an indirect parameter of hydration status, was similar to those described for German children (13), probably reflecting higher non-renal water losses by Portuguese children.…”

“…Friedrich Manz, a brilliant German researcher who proposed the free water reserve algorithm, argued that it was not possible to define a physiological or natural narrow urine osmolality range as it is always influenced by cultural context, namely food habits. This author suggested that only after additionally considering 24 h urine volume, urine solute excretion and maximum urine osmolality, it would be possible to quantify the individual 24 h hydration status (9).…”

Examination of iodine status in the German population: an example for methodological pitfalls of the current approach of iodine status assessment

“…This assumption was questioned repeatedly in the past, as mean urine volume of adults may easily amount to 2 L/day and more [18,[30][31][32]. Accordingly, in a very recent investigation of iodine status in Switzerland, median iodine concentration (measured in 1420 24-h urines) was only 60-70 µg/L, whereas 24-h iodine excretion indicated risk of inadequate iodine status in only 2 % of men and 14 % of women [31].…”

“…Present data basis for adult 24-h creatinine excretion reference values was the 24-h creatinine excretion data from the German VERA study [18][19][20]. The VERA study (Verbundstudie Ernährungserhebung und RisikofaktorenAnalytik) was a representative subsample taken randomly from the first National Food Consumption Survey (NVS I) of the Federal Republic of Germany (1986 and 1988), comprising 2006 subjects, aged 18-88, of whom each subject collected one 24-h urine sample.…”