percentage of water in human body pdf

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Abstract

Total water intake includes drinking water, water in beverages,

and water in food.

Daily water needs determined from fluid balance, water turnover.

or consumption studies provide similar values for a given set of conditions.

A daily water intake of 3.7 L for adult men and 2.7 L for adult women meets the needs of the vast majority of persons.

strenuous physical exercise and heat stress can greatly increase daily water needs.

and the individual variability between athletes can be substantial.

Water as an essential nutrient: the physiologicalbasis of hydration

, University of Lausanne, Pully, Switzerland and2Nestle ́Waters, Paris,

FranceHow much water we really need depends on water functions and the mechanisms of daily water balance regulation.

The aim ofthis review is to describe the physiology of water balance .

and consequently to highlight the new recommendations with regardto water requirements.

Water has numerous roles in the human body.

It acts as a building material; as a solvent, reactionmedium and reactant.

as a carrier for nutrients and waste products; in thermoregulation

and as a lubricant and shock absorber.

The regulation of water balance is very precise, as a loss of 1% of body water is usually compensated within 24h.

waterintake

Both waterintake and water losses are controlled to reach water balance.

Minute changes in plasma osmolarity are the main factors thattrigger these homeostatic mechanisms.

Healthy adults regulate water balance with precision, but young infants .

and elderlypeople are at greater risk of dehydration.

Dehydration can affect consciousness and can induce speech incoherenc.

, extremityweakness, hypotonia of ocular globes, orthostatic hypotension and tachycardia.

Human water requirements are not based on aminimal intake.

(climate, physicalactivity, diet and so on

Water needs are based on experimentally derived intake levels that are expected to meet the nutritionaladequacy of a healthy population.

The regulation of water balance is essential for the maintenance of health and life.

On anaverage, a sedentary adult should drink 1.5l of water per day.

, as water is the only liquid nutrient that is really essential for bodyhydration.

introduction

Water is an essential nutrient for all known forms of life .

and the mechanisms by which fluid and electrolyte homeostasis is maintained in humans are well understood.

Until recently, our exploration of water requirements has been guided by the need to avoid adverse events such as dehydration.

increasing appreciation for the impinging factors that must be considered .

when attempting to establish recommendations of water intake presents us with new and challenging questions.

adverse consequences of inadequate intakes, and factors that affect fluid requirements.

For example, what are the common sources of dietary water and how do they vary by culture.

geography, personal preference, and availability, and is there an optimal fluid intake beyond that needed for water balance?

3 Minimum Water Requirements

The minimum requirement for water is the amount that equals losses.

There are numerous limitations associated with the requirement estimates used to make recommendations.

A review of the research designed to define fluid requirements of humans increases one’s appreciation of the complexity of the issue.

A multitude of intra- and inter-individual factors influence water requirements.

As stated in the 1989 Recommended Dietary Allowances .

(4) establishing a recommendation that meets the needs of all is impossible:

The primary determinant of maintenance water requirement appears to be metabolic,

(Holliday and Segar, 1957) but the actual estimation of water requirement is highly variable and quite complex.

Because the water requirement is the amount necessary to balance the insensible losses .

(which can vary markedly) and maintain a tolerable solute load for the kidneys .

(which may vary with dietary composition and other factors), it is impossible to set a general water requirement.

Factors that increase water requirements

the elderly, and people with certain illnesses may have increased fluid requirements.

and/or present additional challenges in meeting their requirements (19),

space limitations prevent adequate review of such specific populations.

Requirements and recommendations for fluid intake in hot and humid environments will be reviewed here.

because of the inordinate increase in fluid requirements that can result in such conditions .

and the large number of people worldwide who perform work in such environments.

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Thermal and physiological stress

Water lost via sweating is usually low in temperate, sedentary conditions.

but profuse sweating can be a major source of water and electrolyte loss for persons exercising or laboring in extreme heat and/or humidity.

In physically active individuals, sweating presents the most highly variable water loss.

Sweat rates can reach 3 to 4 L/hour,

with variation in sweat rate depending upon exercise intensity.

and duration, age, gender, training, heat acclimatization.

air temperature, humidity, wind velocity, cloud cover, clothing, and individual sweat rate (20).

Total daily fluid requirements

Total daily fluid requirements have been shown to range from as little as 2 liters per day.

to 16 liters per day pending on the work load and the level of heat stress (21).

It has long been known that persons under thermal and physiologic stress need to pay special attention to fluid.

and salt intake (2;22-24). Military personnel have been studied extensively in this regard.

Monographs and scientific publications present some of the extensive research conducted by the United States.

for purposes of survival and endurance during the Second World War (2;25;26).

Scientific findings from the research on military and aerospace personnel continue to provide essential .

and fundamental information on fluid requirements under conditions of thermal and physiologic stress.

Water Intake and Sources

along with relatively small volumes of water created by oxidation of food .

(metabolic water) and breakdown of body tissue. Metabolic water is about 350 to 400 mL/d.

Determining actual water consumption is difficult for a variety of reasons.

one being that many of the published reports are for total water use (drinking water, water used for basic hygiene, etc.).

water

Water (chemical formula H₂O) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance,

which is the main constituent of Earth’s hydrosphere and the fluids of all known living organisms (in which it acts as a solvent^[1]).

Its chemical formula H₂O, indicates that each of its molecules contains one oxygen.

and two hydrogen atoms, connected by covalent bonds.

“Water” is the name of the liquid state of H₂O at standard conditions for temperature and pressure.

A number of natural states of water exist.

It forms precipitation in the form of rain and aerosols in the form of fog.

Clouds consist of suspended droplets of water and ice, its solid state. The gaseous state of water is steam or water vapor.

Regulation of fluid intake

To prevent dehydration reptiles, birds, vertebrates.

and all land animals have evolved an exquisitely sensitive network of physiological controls.

to maintain body water and fluid intake by thirst.

is related to the large capacity of kidneys to rapidly eliminate excesses of water.

Water covers approximately 70.9% of the Earth’s surface, mostly in seas and oceans. Small portions of water occur as groundwater (1.7%), in the glaciers and the ice caps of Antarctica and Greenland (1.7%), and in the air as vapor, clouds (consisting of ice and liquid water suspended in air), and precipitation (0.001%).^[4]^[5] Water moves continually through the water cycle of evaporation, transpiration (evapotranspiration), condensation, precipitation, and runoff, usually reaching the sea.

resource: wikipedia