Hydration and health: a review

Abstract

Water is essential for life and maintaining optimal levels of hydration is important for humans to function well. Water makes up a large proportion of our body weight (60% on average), distributed between the intracellular (inside cells) and extracellular (water in the blood and in between cells) compartments. Water is the major component of body fluids, such as blood, synovial fluid (fluid in the joints), saliva and urine, which perform vital functions in the body. The concentration of solutes (osmolality) in body fluids is closely controlled, and even very small changes in osmolality trigger a physiological response; either to increase body water by reducing urinary output and stimulating thirst; or to excrete excess water as urine. Generally, body water is maintained within narrow limits. However, if water losses are not sufficiently replaced, dehydration occurs. Extreme dehydration is very serious and can be fatal. More mild dehydration (about 2% loss of body weight) can result in headaches, fatigue and reduced physical and mental performance. It is also possible to consume too much water and in rare cases this can result in hyponatraemia (low levels of sodium in the blood).We can get water from almost all drinks and from some foods in the diet. Food provides about 20% on average and this could vary widely depending on the types of food chosen. We also get water from all the drinks we consume, with the exception of stronger alcoholic drinks like wines and spirits. All these can contribute to dietary water, but also have other effects on health both positive and negative. The major concerns with regards to beverages are their energy content and their effect on dental health. With obesity levels continuing to increase it is important for many in the population to control their energy intake, and drinks as well as foods must be considered for their energy content. With regards to dental health, there are two concerns; dental caries and dental erosion. Dental caries are caused by a reduction in pH due to bacterial fermentation of carbohydrates, and so the frequency of consumption of drinks containing sugars is a concern for risk of caries. Dental erosion occurs at a lower pH and is caused by the consumption of acidic foods and drinks, in particular, citrus juices and soft drinks containing acids.Individual water needs vary widely depending on many factors including body size and composition, the environment and levels of physical activity. Thus it is very difficult to make generic recommendations about the amount of water to consume. The FSA currently recommends drinking about 1.2 litres per day (about 6-8 glasses).

An exploration of the hydration care of older people: A qualitative study

“…Further opportunities to boost fluid intake by offering drinks with snacks (Posthauer, 2005, Zizza et al, 2009) and in association with therapy or recreational activities (Frazer, 2008) were evident in the care home although not in the hospital setting. Nurses and HCAs, but not older people were aware that certain foods were a useful source of fluid (Begum andJonhson, 2010, Benelam andWyness, 2010). Taken together these findings suggest that the range of opportunities for promoting hydration was not given sufficient emphasis in practice.…”

The association between water intake, body composition and cardiometabolic factors among children - The Cuenca study

“…In our sample, water (ml)/kg per weight was inversely associated with BMI, body fat, fat free mass and waist circumference, as well as, overweight-obesity children drank less water(ml)/kg per weight than normal weight peers. Healthy eating is one of the keys for obesity prevention (31) and knowledge of the energy contribution from beverages is particularly important, since consumption of healthy fluids is part of a balanced diet (32). Drinking plain water instead of caloric beverages may reduce dietary energy density and help in body weight management (33).…”

Water: neglected, unappreciated and under researched

“…The first is that fluid intake does not have to be water because requirements may be met by other sources of fluid including tea, coffee, milk and food. Secondly,beverages with no or few calories should take precedence over the consumption of beverages with more calories 34 .Thirdly, because of variations in physical activity levels, climate, air conditioning and body size and surface area there is a wide variation in actual fluid requirements.Government guidelines for adequate fluid intake are based on observations.The often quoted "drink at least eight glasses of water a day" has no underpinning scientific evidence 35,36 and does not account for other sources of fluid. While it is recognised that water intake "ahead of thirst" may cause exercise associated hyponatraemia 37 , this is considered a rare occurrence in the general population and there is not enough evidence to set a recommended dietary intake or upper limit for fluid intake.Furthermore there is no clear evidence for lack of benefit of increased water ingestion 38,39 and limited reports of positive effects of water consumption on cognition, physical performance, child health, primary and public health 40 .This limited evidence may be used by Big Food multinationals to help market health 41 and in particular water and the "importance of hydration" 40 .…”