Copeptin is a peptide co-secreted with the antidiuretic hormone vasopressin, which  has recently been used as an indirect marker for bodily hydration. A recent epidemiological study has shown that copeptin is an independent risk factor for diabetes mellitus. This may be related to the expression of vasopressin receptors in the liver and pancreas, key organs involved in glycemic regulation. The present study aimed to assess whether low water intake itself could be associated with an increased risk of hyperglycemia, the first step to diabetes. This hypothesis was tested in the cohort “DESIR”, an epidemiological study of subjects in central France, with a nine-year follow-up period.

Key findings

The study included a total of 3615 adults (aged 30-65 years) with normal glycemia (defined as a fasting blood glucose level not exceeding 1.10 g/L). At inclusion in the study, the participants were administered a lifestyle questionnaire including quantitative estimates of their daily intake of water and other drinks. During the follow-up period, glycemic levels increased to higher than normal values in 565 subjects. Participants who reported drinking less than half a litre of water a day had a 29% higher risk of developing hyperglycemia than those who drank greater volumes. This trend was still observed following adjustment for confounding factors (i.e., gender, age, family history of diabetes and amount of alcoholic or soft drinks consumed). This result was also independent of the amount of physical exercise, and of professional and leisure activities.

Relevance for healthy hydration

The findings of this epidemiological study suggest that it may not be appropriate to keep a low daily water intake for sustained periods of time (subject to medical advice). The relevance of these results to “healthy hydration” should be further investigated in a well-controlled clinical trial involving subjects who spontaneously drink less than half a litre per day. This future study is intended to evaluate participants’ metabolic risk profiles following an intervention consisting in a significant increase in water intake over a period of several weeks. Further experimental research is also required to delineate the mechanisms linking hydration status and glucose metabolism.

Roussel R, Fezeu F, Bouby N, Balkau B, Lantieri O, Alhenc-Gelas F, Marre M, Bankir L; D.E.S.I.R. Study Group. Low water intake and risk for new-onset hyperglycemia. Diabetes Care. 2011;34(12):2551-4. Epub 2011 October 12. http://www.ncbi.nlm.nih.gov/pubmed/21994426

They studied the effects of mild dehydration (1 to 2% measured with very accurate balances) on cognitive function and exercise in young healthy men and women using identical protocols. They found both groups felt tired and had a lower cognitive performance (decreased vigilance) in the dehydrated state. Furthermore, the men appeared to have small problems with short-term memory whereas the women reported confusion, headache and lack of energy thus difficulty with moderate exercise. These results would suggest that a small degree of dehydration, especially if it was chronic, could have detrimental effects on our overall performance in almost every aspect of our daily living. In a normal home environment access to water is not restricted and thus it should be possible to achieve optimal hydration, at least at the beginning and the end of each day. However, it is what happens in the work situation that could pose serious questions as to the cognitive and physical capacity of everyone where access to fluid for optimal hydration is not necessarily encouraged. Coffee and tea breaks are limited and could be dehydrating whereas not all businesses have beverage distributers or water fountains. It would now be very interesting to repeat the same experiments using mild hyper-hydration instead, to see if this would have a positive influence on cognitive and physical abilities.

Introduction

It is well known that ensuring an adequate level of hydration plays an important role in overall health, including maintaining brain function.  Scientific research on dehydration induced by high heat and exercise has shown that mental function (cognition) is greatly affected by severe dehydration.
Recently two large, carefully designed studies were conducted at the University of Connecticut, USA, to examine the effects of mild dehydration on cognitive function in healthy individuals.  To measure mental function, tests of cognitive performance, mood and symptoms of dehydration were used by the scientists.  One study was conducted with 26 men and another with 25 women.  Both studies examined the effects of mild dehydration on cognitive function using identical procedures.  Men and women all took part in two mildly dehydrated conditions and a fully hydrated condition which could be directly compared using standard statistical procedures. To assess the level of dehydration, body weight was measured using special, high accuracy scales.  Men on average were 1.59% dehydrated, women were 1.36% dehydrated.  Most adults reach this level of dehydration one or more times during the course of a week.

Key Findings

The results showed that, in both men and women, mild dehydration had an adverse effect on mood as well as ability to concentrate. When mildly dehydrated, both men and women were  more likely to feel fatigued and to have diminished cognitive performance, specifically vigilance.  Men were more likely to experience short-term memory degradation when mildly dehydrated, but overall, women were more sensitive to dehydration than men.  For example, women were more likely to report a headache, fatigue, confusion and lack of energy. Women also felt moderate exercise was more difficult when dehydrated.

Relevance for healthy hydration

These studies provide a better understanding of the effects of mild dehydration on cognitive function of men and women and have many practical applications.  They demonstrate the importance of maintaining optimal levels of hydration during normal daily activities and during moderate exercise.  Both men and women will perform better and feel better if they maintain full hydration by regularly consuming water.  In addition, vulnerable populations such as elderly people and children may be more susceptible to the adverse effects of dehydration on mood and cognitive performance.

Dehydration profoundly influences mental performance, neuroexcitability and possibly survival of neurons. The molecular neuronal mechanisms sensitive to dehydration remained, however, incompletely understood. The present study addressed the effect of water deprivation on gene expression in the brain. To this end, mice were exposed to a 24 hours deprivation of drinking water and neuronal gene expression was determined by microarray technology with subsequent confirmation by RT-PCR and partially Western blotting.

Key Findings

Water deprivation was followed by alterations of cerebral gene expression. Specifically dehydration upregulated the transcript levels of clathrin (light polypeptide Lcb), serum/glucocorticoid-regulated kinase (SGK) 1, and protein kinase A (PRKA) anchor protein 8-like. Water deprivation led to downregulation of janus kinase and microtubule interacting protein 1, neuronal PAS domain protein 4, thrombomodulin, purinergic receptor P2Y – G-protein coupled 13 gene, gap junction protein beta 1, neurotrophin 3, hyaluronan and proteoglycan link protein 1, G protein-coupled receptor 19, CD93 antigen, forkhead box P1, suppressor of cytokine signaling 3, apelin, immunity-related GTPase family M, serine (or cysteine) peptidase inhibitor clade B member 1a, serine (or cysteine) peptidase inhibitor clade H member 1, glutathion peroxidase 8 (putative), discs large (Drosophila) homolog-associated protein 1, zinc finger and BTB domain containing 3, and H2A histone family member V. In conclusion, water deprivation influences the transcription of a wide variety of genes in the brain, which may participate in the orchestration of brain responses to water deprivation.

Relevance for healthy hydration

The observations provide novel insight into the molecular consequences of inadequate hydration. They help to understand, how inadequate hydration could possibly affect mental performance, neuroexcitability and possibly survival of neurons. An influence on neuronal survival would have lasting effects on mental health. Future studies are required to bridge the molecular knowledge to the phenomenology of the interaction between hydration status and brain function.

This study describes the rate of absorption of water in the body water pool and the volume and rate of renewal of this pool. The experiment was conducted on 36 healthy male subjects (18-35 yo, 76.9 kg, BMI = 23.3 kg/m2) drinking ad libitum, with 2 L/day of natural mineral water in their beverages. Following ingestion of natural mineral water with deuterium oxide (D2O) as tracer, the deuterium to hydrogen ratio (D/H) was measured in blood over the following hour and in urine over the following 9 days.

Pharmacokinetic analysis of D/H show that water appeared in plasma and blood cells within 5 min following ingestion and was entirely distributed in the body water pool within ~75-120 min. The volume of the body water pool was 46.6 L (60.7 % body mass) and its turnover (or water clearance, i.e., the volume added in the pool from water in food and drinks and metabolic water, and removed from the pool through urine, feces, sweat, perspiration, and respiration, was 4.58 L/day.  The mean residence time of water in the body water pool was 10.3 days indicating that half of the pool (i.e., the half-life) was replaced in 7.2 days.

Water ingested under the form of natural mineral waters, with a low mineral content, appears in plasma and blood cells in less than 5 min, and is distributed in the entire body water pool in less than 2 hours. In the young healthy male subjects studied who remained well hydrated by drinking 2 L of natural mineral water/day, the entire body water pool was completely renewed in ~50 days.

Introduction

Kidney stones affect around 10% of the population and the incidence is increasing in many countries. Medical expenditures due to this condition are very high and rising concomitantly. In most cases, prevention of stone recurrence is based on dietary advice. It has been observed that a sufficient water intake, producing at least 2L/d urine, dilutes urine and lowers kidney stone formation risk. The purpose of this study therefore was to measure the effects of a daily additional 2L of water on a kidney stone risk indicator, called the crystallization risk index. Forty-eight volunteers were divided into two groups, control and treated. Following a baseline observation period, the “treated group” drank an additional 2L/d water load, while the “control group” had their usual fluid intake. Treated and control volunteers were compared at the end of the study.

Key Findings

The crystallization risk index significantly decreased in the treated group with the additional water intake, compared with the control group. The absolute daily additional water intake was actually 1.3 L/d in the treated group, because volunteers decreased their other usual fluid sources.

Relevance for health

This study demonstrates that increasing daily water intake to 1.3 L/d, and thus urinary volume, reduces the crystallization risk index and thus kidney stone risk.

My research group recently performed a study to investigate the impact of an educational intervention on the hydration state of 92 young volleyball and basketball players participating in a five day training camp.

At the start of the study, we found that more than 90% of the kids taking part were inadequately hydrated and most did not realize that their bodies were lacking water. Following this observation, we randomized half of the participants to either the control or the educational intervention group. The intervention group received a lecture about the importance of everyday hydration; hadurine color charts placed in their bathrooms; and were given increased water availability. Kids were also weighed before and after training in order to understand the concept that decreasing body weight during exercise is nothing more than dehydration.

We found that the group receiving the educational intervention improved their hydration state (as assessed by urine specific gravity and urine osmolality) and were able to run faster in a 600 meter running test. On the other hand, we did not find any significant improvement in hydration or performance in the control group. We were encouraged by our results as they suggest that similar educational programs can be used to effectively improve hydration and performance in young people.

I’ve enjoyed sharing the findings of this study with you and I’d be really pleased to know what you think. If you’d like to download the publication and find out more, please visit the Emerging Hydration Science section.

Introduction

It has been well documented that a large percentage of both amateur and professional athletes start their training and/or competitions inadequately hydrated. Furthermore, even in optimal conditions with water and/or sports drinks availability, athletes of all ages tend to become dehydrated during exercise. Therefore, the purpose of our study was to investigate the effect of a nutrition intervention program, emphasising water consumption on the prevention of dehydration and exercise performance in young athletes. A total of 92 young trained volleyball and basketball athletes participating in a five day training camp were randomised to either the control (CON) or the intervention (INT) group.

Key Findings

More than 90% of the participants started the training camp inadequately hydrated. Only the INT group improved hydration status, resulting in enhanced running endurance performance, as a response to the intervention. No significant improvement in hydration or performance was found in the CON group.

Relevance for health

This study showed that a simple educational program, consisting of a lecture on hydration, use of the urine color chart, improved water availability, and body weighting before and after exercise in some practices, was effective in improving hydration. We also found that improving hydration status by ad libitum consumption of water can enhance performance in young athletes exercising in the heat. Similar educational programmes can be used to effectively improve hydration and performance in free living active youth.