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Increased insensible water loss contributes to aging related dehydration.

Dmitrieva NI, Burg MB - PLoS ONE (2011)

Bottom Line: All 3 groups maintain water balance while consuming only the water in gel food containing 56% water.However, both older groups excrete a smaller volume of urine of higher osmolality, indicating greater extra urinary water loss.The greater insensible water loss occurs at an earlier age (18 months) than decreased urine concentrating ability (27 months).

View Article: PubMed Central - PubMed

Affiliation: Laboratory of Kidney and Electrolyte Metabolism, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland, United States of America. dmitrien@nhlbi.nih.gov

ABSTRACT
Dehydration with aging is attributed to decreased urine concentrating ability and thirst. We further investigated by comparing urine concentration and water balance in 3, 18 and 27 month old mice, consuming equal amounts of water. During water restriction, 3 month old mice concentrate their urine sufficiently to maintain water balance (stable weight). 18 month old mice concentrate their urine as well, but still lose weight (negative water balance). 27 month old mice do not concentrate their urine as well and lose even more weight than the 18 month old mice, indicating a larger negative water balance. Negative water balance in older mice is accompanied by increased vasopressin excretion, providing further evidence of dehydration. All 3 groups maintain water balance while consuming only the water in gel food containing 56% water. However, both older groups excrete a smaller volume of urine of higher osmolality, indicating greater extra urinary water loss. Since their feces also contain less water, the excess water lost by the older mice apparently is through other routes, presumably insensible loss through the respiratory tract and skin. The greater insensible water loss occurs at an earlier age (18 months) than decreased urine concentrating ability (27 months). We propose that insensible water loss through skin and respiration increases with age, making a major contribution to aging related dehydration.

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Analysis of hydration based on changes of body weight.A) Changes of body weight resulting from decreased water intake in mice of different ages. Data are presented as % weight change relative to the weight at the beginning of the experiment (median and IQR, n = 3–4, * P<0.05 relative to 3 month old mice; # P<0.05 relative to 0 time; † P<0.05 relative to 18 month old mice). 3 month old mice do not lose weight, despite decreasing water intake. 18 and 27 month old mice lose weight when water content of the gel food falls to 43% - 33%. 27 month old mice lose the most weight and are very dehydrated by the end of the experiment. B) Reversal of progressive weight loss when low water content of the gel food is increased. 16 month old mice were subjected to consecutive periods (3 days each) of 43%, then 33% water in their gel food, which caused weight loss that progressed over 6 days. On day 7 when the water content of the gel food was increased to 56%, the mice began regaining weight. This rapid onset of weight gain when water intake was increased supports our use of weight as a measure of water balance. Data are plotted as Median and IQR; n = 4, (#) P<0.05 relative to 0 time. (*): P = 0.06 if Mann-Whitney Test (one-tailed, paired) is used, P = 0.002 if Student t-test (one-tailed, paired) is used. Note: the experiments shown on panels A and B are not directly compatible because the diets differed (see Methods for details).
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pone-0020691-g002: Analysis of hydration based on changes of body weight.A) Changes of body weight resulting from decreased water intake in mice of different ages. Data are presented as % weight change relative to the weight at the beginning of the experiment (median and IQR, n = 3–4, * P<0.05 relative to 3 month old mice; # P<0.05 relative to 0 time; † P<0.05 relative to 18 month old mice). 3 month old mice do not lose weight, despite decreasing water intake. 18 and 27 month old mice lose weight when water content of the gel food falls to 43% - 33%. 27 month old mice lose the most weight and are very dehydrated by the end of the experiment. B) Reversal of progressive weight loss when low water content of the gel food is increased. 16 month old mice were subjected to consecutive periods (3 days each) of 43%, then 33% water in their gel food, which caused weight loss that progressed over 6 days. On day 7 when the water content of the gel food was increased to 56%, the mice began regaining weight. This rapid onset of weight gain when water intake was increased supports our use of weight as a measure of water balance. Data are plotted as Median and IQR; n = 4, (#) P<0.05 relative to 0 time. (*): P = 0.06 if Mann-Whitney Test (one-tailed, paired) is used, P = 0.002 if Student t-test (one-tailed, paired) is used. Note: the experiments shown on panels A and B are not directly compatible because the diets differed (see Methods for details).

Mentions: Body weight is a simple and accurate index of hydration when serial measurements are made in close proximity [12]. As long as water input and output are balanced, body weight stays constant. Acute dehydration is reflected by an immediate decrease in body weight. Figure 2A shows the change in body weight of mice of different ages as their water intake is decreased. When their gel food contains 56% water, mice of all ages maintain water balance, as indicated by constant weight. With reduced water intake 3 months old mice maintain water balance, as indicated by a near constant weight (that initially even increases slightly). In contrast, 18 and 27 month old mice become dehydrated (lose weight) when there is less than 50% water in their gel food, and dehydration becomes progressively severe as water intake falls further. The dehydration is greater in 27 month old than 18 month old mice. Fast recovery of weight after water intake increased supports the conclusion that the weight loss during water restriction was caused by dehydration (Fig. 2B).


Increased insensible water loss contributes to aging related dehydration.

Dmitrieva NI, Burg MB - PLoS ONE (2011)

Analysis of hydration based on changes of body weight.A) Changes of body weight resulting from decreased water intake in mice of different ages. Data are presented as % weight change relative to the weight at the beginning of the experiment (median and IQR, n = 3–4, * P<0.05 relative to 3 month old mice; # P<0.05 relative to 0 time; † P<0.05 relative to 18 month old mice). 3 month old mice do not lose weight, despite decreasing water intake. 18 and 27 month old mice lose weight when water content of the gel food falls to 43% - 33%. 27 month old mice lose the most weight and are very dehydrated by the end of the experiment. B) Reversal of progressive weight loss when low water content of the gel food is increased. 16 month old mice were subjected to consecutive periods (3 days each) of 43%, then 33% water in their gel food, which caused weight loss that progressed over 6 days. On day 7 when the water content of the gel food was increased to 56%, the mice began regaining weight. This rapid onset of weight gain when water intake was increased supports our use of weight as a measure of water balance. Data are plotted as Median and IQR; n = 4, (#) P<0.05 relative to 0 time. (*): P = 0.06 if Mann-Whitney Test (one-tailed, paired) is used, P = 0.002 if Student t-test (one-tailed, paired) is used. Note: the experiments shown on panels A and B are not directly compatible because the diets differed (see Methods for details).
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Related In: Results  -  Collection

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pone-0020691-g002: Analysis of hydration based on changes of body weight.A) Changes of body weight resulting from decreased water intake in mice of different ages. Data are presented as % weight change relative to the weight at the beginning of the experiment (median and IQR, n = 3–4, * P<0.05 relative to 3 month old mice; # P<0.05 relative to 0 time; † P<0.05 relative to 18 month old mice). 3 month old mice do not lose weight, despite decreasing water intake. 18 and 27 month old mice lose weight when water content of the gel food falls to 43% - 33%. 27 month old mice lose the most weight and are very dehydrated by the end of the experiment. B) Reversal of progressive weight loss when low water content of the gel food is increased. 16 month old mice were subjected to consecutive periods (3 days each) of 43%, then 33% water in their gel food, which caused weight loss that progressed over 6 days. On day 7 when the water content of the gel food was increased to 56%, the mice began regaining weight. This rapid onset of weight gain when water intake was increased supports our use of weight as a measure of water balance. Data are plotted as Median and IQR; n = 4, (#) P<0.05 relative to 0 time. (*): P = 0.06 if Mann-Whitney Test (one-tailed, paired) is used, P = 0.002 if Student t-test (one-tailed, paired) is used. Note: the experiments shown on panels A and B are not directly compatible because the diets differed (see Methods for details).
Mentions: Body weight is a simple and accurate index of hydration when serial measurements are made in close proximity [12]. As long as water input and output are balanced, body weight stays constant. Acute dehydration is reflected by an immediate decrease in body weight. Figure 2A shows the change in body weight of mice of different ages as their water intake is decreased. When their gel food contains 56% water, mice of all ages maintain water balance, as indicated by constant weight. With reduced water intake 3 months old mice maintain water balance, as indicated by a near constant weight (that initially even increases slightly). In contrast, 18 and 27 month old mice become dehydrated (lose weight) when there is less than 50% water in their gel food, and dehydration becomes progressively severe as water intake falls further. The dehydration is greater in 27 month old than 18 month old mice. Fast recovery of weight after water intake increased supports the conclusion that the weight loss during water restriction was caused by dehydration (Fig. 2B).

Bottom Line: All 3 groups maintain water balance while consuming only the water in gel food containing 56% water.However, both older groups excrete a smaller volume of urine of higher osmolality, indicating greater extra urinary water loss.The greater insensible water loss occurs at an earlier age (18 months) than decreased urine concentrating ability (27 months).

View Article: PubMed Central - PubMed

Affiliation: Laboratory of Kidney and Electrolyte Metabolism, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland, United States of America. dmitrien@nhlbi.nih.gov

ABSTRACT
Dehydration with aging is attributed to decreased urine concentrating ability and thirst. We further investigated by comparing urine concentration and water balance in 3, 18 and 27 month old mice, consuming equal amounts of water. During water restriction, 3 month old mice concentrate their urine sufficiently to maintain water balance (stable weight). 18 month old mice concentrate their urine as well, but still lose weight (negative water balance). 27 month old mice do not concentrate their urine as well and lose even more weight than the 18 month old mice, indicating a larger negative water balance. Negative water balance in older mice is accompanied by increased vasopressin excretion, providing further evidence of dehydration. All 3 groups maintain water balance while consuming only the water in gel food containing 56% water. However, both older groups excrete a smaller volume of urine of higher osmolality, indicating greater extra urinary water loss. Since their feces also contain less water, the excess water lost by the older mice apparently is through other routes, presumably insensible loss through the respiratory tract and skin. The greater insensible water loss occurs at an earlier age (18 months) than decreased urine concentrating ability (27 months). We propose that insensible water loss through skin and respiration increases with age, making a major contribution to aging related dehydration.

Show MeSH
Related in: MedlinePlus