June/July 2022 Issue

CPE Monthly: Dehydration, Cognition, and Health
By Sara Chatfield, MPH, RDN, LDN
Today’s Dietitian
Vol. 24, No. 5, P. 40

Suggested CDR Performance Indicators: 8.1.1, 8.1.4, 10.2.1, 10.2.5
CPE Level 2

Take this course and earn 2 CEUs on our Continuing Education Learning Library

Water is essential to all life; in humans, water performs critical functions such as regulating body temperature; maintaining blood volume, circulation, and the lymphatic system; providing solutes for cellular reactions; transporting nutrients; and aiding digestion, absorption, and excretion.1-3 About two-thirds of body water is intracellular, with one-third extracellular and about 3% transcellular.1

At birth, water accounts for 75% to 85% of body weight, decreasing to about 60% to 70% in adults, although this varies with age, sex, and body composition; water comprises 45% to 55% of body weight in adults with obesity and about 50% of body weight in older adults.1,3 However, body water percentage remains fairly consistent in each individual from day to day.1

Lack of adequate safe drinking water is an urgent concern in many areas of the world and during emergencies and disasters. Worldwide, about 785 million people, many of whom live in sub-Saharan Africa, lack safe drinking water.4 Climate change, economic development, and growing populations are affecting the availability of potable water, and it’s predicted that by 2025 the number of people in water-stressed areas will have expanded to include one-half of the world’s population.5

This continuing education course identifies the functions of water in the human body, highlights fluid needs in a variety of life stages and health conditions, and examines the factors involved in fluid balance and dehydration, along with associated cognitive and health impacts.

Water Homeostasis
Body water homeostasis is maintained by the brain, kidneys, and gastrointestinal (GI) tract to within about 0.2% body weight over the course of a day in healthy adults at rest.6,7 Osmoreceptors in the brain detect dehydration via increased serum osmolality, which is the quantity of solutes per unit of water, or decreased blood volume, triggering thirst in the hypothalamus and leading it to release the antidiuretic hormone arginine vasopressin (AVP). AVP activates the kidneys’ conservation of water by reabsorption, and by decreasing urine volume and increasing urine concentration.6,8

Thirst generally is perceived after a fluid loss of 1% to 2% body mass.1,6,8 In addition to those in the hypothalamus, osmoreceptors in the oropharynx, GI tract, and liver portal system influence thirst.6 Thirst also is affected by sensory input from fluid in the oropharynx and esophagus.9

Some studies have identified weaker thirst signals in chronically low water drinkers than in those who drink more.10 Thirst sensitivity also is lower in infants and older adults, and may be lower in individuals with acute or chronic illnesses, dementia, or history of stroke.6 During exercise, thirst often doesn’t occur until a fluid loss of 2% body mass, increasing the risk of dehydration.1,11

Fluid Balance
Fluid intake from foods and beverages and the small amount produced by metabolic water production is balanced by the body’s fluid losses. Metabolic water production occurs during the body’s metabolism of nutrients into energy and, depending on the composition of macronutrients in an individual’s diet, can average 250 to 350 mL per day in sedentary
individuals and 500 to 600 mL per day in physically active individuals.6

Water from beverages contributes an estimated 70% to 80% of an individual’s fluid intake, the rest being from food.3 Limited research indicates that various dietary factors may impact fluid balance, though these effects generally seem to be mild.

Urea, a metabolic end product of dietary protein, requires water for excretion from the kidneys. However, one study with eight men showed that increasing dietary protein intake for seven days didn’t affect fluid intake or urine volume when water was provided ad lib. Caffeine has a diuretic effect, and studies suggest doses higher than 180 mg per day increase urinary output for a short period but likely don’t lead to significant loss of body fluid. Similarly, the diuretic effect of alcohol appears to be temporary and unlikely to cause significant fluid losses.6

The effect of sodium on fluid balance may vary among individuals; one study with 24 men noted little change in their urine volume with varying levels of dietary sodium intake for seven days, but another study showed significantly higher urine excretion in 104 hypertensive men and women who consumed high vs low levels of sodium over five days.6

Standard daily fluid losses include a typical urine output of 1 to 2 L per day, with a range of 500 mL per day (or less with dehydration) to 20 L per day, varying with hydration status, physical activity level, environment, solutes needing excretion, and urine concentrating ability. Fecal water losses average about 100 to 200 mL of fluids per day in healthy adults.6 Perspiration fluid losses are estimated at about 450 mL per day in an average adult, with lower levels in the elderly and higher levels in adolescent and adult males.12 Respiratory fluid losses are about 250 to 350 mL per day in sedentary people and about 500 to 600 mL per day in active people, increasing with dry, hot, or cold air and high altitude.6

Fluid Requirements and Intake
Human fluid requirements are challenging to determine, due to the complexity of the water regulatory system and the wide variation in individual needs with regard to age, sex, body composition, physical activity level, diet, and physical and social environment.6,8,13 There’s also a scarcity of research on the water intake of individuals in various life stages and environments.2

Studies have shown that a daily minimum of 0.91 L of water, and 3 L in hot weather, is needed for survival in adults, with the daily minimum to replace fluid losses—for inactive adults in temperate climates—being in the range of 1 to 3.1 L.6 As such, the World Health Organization recommends each individual have access to 2.5 to 3 L of water per day.2

Adequate Intakes (AIs) for water were set by the Food and Nutrition Board of the Institute of Medicine and are meant to meet the needs of “almost everyone” in each age/life stage category (see table below). They were based on the median total water intake in each group in National Health and Nutrition Examination Survey (NHANES) III data, rounded to the nearest 0.1 L.6

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In addition to homeostatic mechanisms and thirst, psychological and social cues play an important role in fluid intake, with much consumption occurring during meals.9 Fluid intake can be impacted by the perceived palatability of beverages; factors such as appearance, flavor, odor, and temperature; and by cultural preferences. One study showed that men drank the most when water temperature was 59° F, despite rating the cooler water as more pleasurable. In a study of children exercising in the heat, ad lib consumption of fluids was found to be greater with flavored than with unflavored water.6

Dehydration has been defined variously as a process of losing water, a deficiency of body water, and a loss of water greater than 2% of body weight, with mild dehydration a loss of 1% to 2% of body weight.14,15

Healthy adults can live up to 10 days without water, children up to five days.1 A water loss of 10% body weight can damage essential body systems, increases the risk of death in animal studies, and in case observations has contributed to potentially deadly heat stroke; most people require medical assistance at this degree of dehydration.6 A fluid loss of 20% body mass can cause death.1

Dehydration can be caused by decreased fluid intake due to anorexia, nausea, impaired thirst, dysphagia, depression, altered mental status, or mobility issues that impair access to fluids. Other causes include severe loss of water and electrolytes from various routes such as sweating, vomiting, diarrhea, fever, laxative overuse, diuretics, excessive urination, fistulas, GI suction, and burns.1

Fluid balance is commonly altered in hospitalized patients affected by protein-energy malnutrition, trauma, surgery, and various conditions, such as severe skin disease, renal failure, hyperglycemia, and sepsis.1 Increased blood urea nitrogen (BUN), a marker of dehydration, is associated with worse outcomes in critically ill patients.15

Dehydration appears to increase the risk of death in hospitalized older adults; research has shown that almost one-half of adults aged 65 and older admitted to the hospital with a primary diagnosis of dehydration died within one year of hospitalization, and 17.4% of them died within 30 days. An accompanying diagnosis of dehydration in patients also has been linked with significantly higher mortality rates within 30 days to one year. In observational studies, dehydration has been associated with increased mortality in stroke patients in the United Kingdom, older US adults with diabetes mellitus, and community-dwelling older US adults.15

Rapid fluid replacement generally is recommended in patients with serious dehydration, but a more cautious approach may be needed with older adult patients, or those with heart or kidney failure. Isotonic fluid solutions such as normal saline most commonly are used but must be tailored to patients’ needs.7

Types of Dehydration
The type of dehydration depends on the cause and degree of water loss as well as the proportions of water vs electrolytes lost. In isotonic dehydration, water and sodium are lost proportionally. Examples of causes include vomiting, diarrhea, sweating, burns, acute renal failure, hyperglycemia, hypoaldosteronism, and ascites.7,11,16

In hypertonic dehydration, water losses exceed sodium losses, and serum sodium and osmolality are elevated. This often is due to insufficient fluid intake or excessive sweating, but other causes include fever, increased respiration, and diabetes insipidus.7,15 In hypotonic dehydration, sodium losses exceed water losses, and sodium and osmolality levels are low; diuretics are the most common cause.7

Signs and Symptoms of Dehydration
One sign of dehydration is rapid weight loss. Greater than 3% body weight lost over seven days is an indicator, but a more gradual process of dehydration and weight loss may be more difficult to identify.3,17 Other symptoms may include dark urine, decreased urine output, fatigue, headache, irritability, disorientation, muscle cramps, dry and furrowed tongue, lowered body temperature, cold extremities, dizziness, postural hypotension, weak and rapid pulse, slow capillary refill, palpitations, and dry skin, lips, and mucous membranes.1,7,18

Some signs and symptoms may not correlate with biochemical measures of dehydration, suggesting a lack of reliability.3 Signs that have helped to identify dehydration in children include decreased urine output, decreased skin elasticity, sunken eyes, tachycardia, and abnormal respiratory pattern, capillary refill time, or pulse. Some of these signs may be unreliable in older adults.3 In small studies, signs that were associated with imminent dehydration in people older than 65 were fatigue or missing drinks between meals, and these indicators were more accurate when combined but didn’t effectively identify current dehydration.17

Several measures and tests are used to assess dehydration, though there’s no gold standard and it’s more challenging to identify mild to moderate levels of dehydration due to body fluid fluctuations.7,18 Some markers can be used more easily at home or in field settings, such as scales indicating thirst or urine color and weight changes, with two or more positive measures signifying dehydration.11

Hydration-Related Lab Tests

Plasma Osmolality
Studies have found a strong negative relationship between changes in total body water and plasma osmolality levels. A normal plasma osmolality range is around 285 to 290 or 295 mOsm/kg, with adults older than 70 having slightly higher levels.6-8,15 This test may have lower validity when water status is in flux and won’t identify isotonic dehydration, in which osmolality remains constant.6,8,15

Elevated serum sodium levels can indicate dehydration but may be a less sensitive measure of dehydration than serum osmolality and less accurate, as levels depend on the type of dehydration.3

When kidney function is normal, higher levels of BUN and a BUN-to-creatinine ratio of greater than 10:1 may indicate dehydration, although these measures lack specificity.7

Urine Tests
Tests of urine volume, osmolality, and specific gravity tend to be more sensitive to lower levels of dehydration than other measures. In research, a cutoff of 800 mOsm/kg urine osmolality has been used to identify normal hydration, with higher levels indicating low fluid balance. Increases in urine osmolality signify fluid loss when solute levels remain consistent, but test accuracy can be impacted by the timing and amount of water intake.6,18,19 Normal urine specific gravity ranges are around 1.01 to 1.025 or 1.03, with higher levels suggesting fluid loss, and levels above 1.03 indicating dehydration. This test may not be accurate in older adults, as it also reflects the kidneys’ ability to concentrate urine.6,11,20

Dehydration Risk by Life Stage

Pregnant and Lactating Women
Fluid needs are higher during pregnancy due to total fluid gains of 6 to 9 L, including about 1.8 to 2.5 L of intracellular fluid. Temporary differences in plasma osmolality occur in pregnancy unrelated to hydration levels.6 Pregnant women in areas that lack safe drinking water face a higher risk of inadequate fluid intake.16,21

There’s evidence that adequate fluid intake during pregnancy is related to amniotic fluid volume and that additional fluid may help when amniotic fluid volume is low. Some observational data suggest that dehydration in the later stages of pregnancy is linked to lower birth weight of the infant.21 Some studies have shown a shortened duration of labor with IV fluid therapy.16,21

Lactating women require additional fluids for milk production. For the first six months of lactation, the average milk production contains an amount of water similar to the difference between the AI for nonpregnant or lactating women and the AI for lactation, which is based on median fluid intake in this population.6 Generally, lactation doesn’t seem to heighten the risk of dehydration; however, lactating women in hot climates with low water security have been found to have higher urine specific gravity and significantly higher odds of dehydration than nonlactating women.6,21

There’s limited research on hydration needs during infancy. Infants are at higher risk of dehydration due to their higher total body water content, higher rate of water turnover (which decreases rapidly between infancy and early childhood), less-developed sweating mechanisms, comparatively limited ability to excrete solutes, and decreased ability to express thirst compared with adults.6

Children may be more prone to dehydration, given their higher surface area-to-volume ratio, higher activity levels, and less mature thirst mechanisms compared with adults. In addition, social factors, eg, dependency on others for access to water, are significant.14

A study of NHANES data showed that 54.5% of children aged 6 to 19 were inadequately hydrated, defined by urine osmolality greater than or equal to 800 mOsm/kg. Boys, younger children, and Black non-Hispanic children—vs white non-Hispanic children—were more likely to be inadequately hydrated; there was no association with family income. Higher intake of plain drinking water was linked with decreased odds of inadequate hydration.18

Studies of children and adolescents attending school in warm climates have found that more than one-half of students, and up to 90% in one study of 41 adolescent boys, were inadequately hydrated according to urine tests.22-24 Seriously dehydrated students (one-half of students in one study) reported feeling less alert.24 Factors associated with increased risk of inadequate hydration were male sex and higher levels of physical activity; girls were noted to have higher intake of water-dense foods such as fruits and vegetables.22

According to the limited data available, children and adolescents seem to be at relatively high risk of inadequate hydration, particularly in hot weather and when engaging in higher levels of physical activity.

Analyses of NHANES data have found that significant numbers of US adults are at risk of inadequate hydration. In one study, approximately 40% of adults aged 20 to 50 and 50% of adults aged 51 to 70 failed to meet AIs for water; in both age groups, more men than women failed to meet recommendations.25 Another study found water-loss dehydration in 16% of 20- to 29-year-olds, 26% of 50- to 69-year-olds, and 28% of 70- to 90-year-olds, with rates being higher in men in each group.3

Older Adults
In older adults, age-related changes, including lowered basal total body water and impairments in renal concentrating ability, AVP responses, and thirst sensitivity, increase the risk of inadequate hydration.6,8,26 Due to these combined risk factors, drinking only in response to thirst may not be adequate for older adults to meet fluid needs.9

Older adults are about 20% to 30% more likely to develop dehydration than younger people.7,9 Some national surveys have found that the majority of older adults failed to meet AIs for fluid.26 In one analysis of NHANES data from 2005–2010 for adults aged 71 and older, 94.7% of men and 82.6% of women failed to meet AIs for total water.25 Dehydration in older adults is associated with a variety of negative outcomes, including confusion, falls, and chronic health problems.3

Dehydration is a common cause of hospital admission in older adults.6,7,9,15 In a study of patients aged 65 and older who were admitted to the hospital, 40% were found to be dehydrated on admission and 44% were dehydrated 48 hours later, according to serum osmolality values.17

Nursing home residents may be at particular risk of dehydration, though statistics vary and lack of data makes it difficult to determine how to best increase fluid intake.15,27 Residents have reported many issues interfering with fluid intake, including taste preferences and impaired taste, social isolation, dementia, communication issues, physical inability to access their own drinks, and concerns about needing to use the bathroom more frequently. Several strategies have been proposed to encourage fluid intake in residents, including education of residents, families, and staff on the risks of dehydration, ensuring appropriate staffing, providing continual access to drinks within reach and according to preferences, increasing opportunities for socialization while eating/drinking, and using brightly colored cups.3,27

One intriguing study comparing the urine-specific gravity and urine osmolality values of US adults aged 18 to 80 with those of Bolivian Tsimané forager horticulturalists and Tanzanian Hazda hunter-gatherers of similar age range found a significantly greater decline in urine concentrating ability with age in the US adults compared with the other two populations. The authors proposed that the decline in the kidneys’ ability to concentrate urine and the associated increase in dehydration risk, which occurs with increasing age in the United States, may be affected by environmental factors such as lower physical activity levels and consumption of a typical Western diet.28

Physical activity increases water requirements proportionally to individuals’ increased fluid losses in sweat. Athletes can have sweat losses of approximately 0.3 to 2.4 L per hour, depending on the intensity and duration of exercise; environmental factors such as altitude, humidity, and temperature; and individual differences such as fitness level, body mass, and heat acclimatization.11,20 Children’s additional fluid needs for physical activity may be less due to their smaller body size and lower sweat production.6,11 The risk of dehydration in athletes increases with prolonged, back-to-back training sessions and purposeful fluid restriction for weigh-ins.11,20

Studies have shown adverse effects of dehydration on aerobic exercise performance after fluid losses of 1% to 2% body weight, with larger fluid losses and the addition of heat stress leading to more dramatic decreases, but most research hasn’t found decreases in muscular strength until fluid losses reach 3% to 5% body weight.6,11,20,29 It’s been theorized that dehydration’s impact on aerobic performance is due to circulatory strain.30 Fluid loss of 6% to 10% body weight has produced more extreme effects on exercise tolerance and may affect cardiac output.20

To maintain optimal hydration, it’s generally recommended that athletes consume approximately 5 to 10 mL of fluids per kg body weight about two to four hours before exercise, but needs vary based on factors such as athletes’ body weight and fitness level and the type and duration of exercise.20 Intake of electrolytes and supplemental carbohydrates can help with fluid retention during prolonged, intense exercise.11,20 Monitoring simple hydration signs such as checking urine for pale yellow color may help to ensure adequate hydration before events.20

Rehydration in athletes with dehydration also should be tailored to the individual, but general recommendations are about 1.25 to 1.5 L fluid for every kg of body weight lost.20 Research in athletes with dehydration has linked rehydration of 0.5 to 1.15 L per kg of body weight lost to improved performance during continuous exercise. However, effects on intermittent performance, resistance exercise, and sport-specific skills were less clear.29 During rehydration, it’s important to monitor hydration status, as thirst satiation may occur before changes in plasma osmolality.9

Health Effects of Dehydration

Cognition and Mood
There’s significant research suggesting that hydration is important for cognition. Some studies have shown that inadequate hydration is associated with poorer performance on cognitive tests, but the link is difficult to assess due to the scarcity of research demonstrating causality and a lack of standardization in cognitive testing.14,18 In addition, there’s a noted lack of studies in this area in women, sedentary adults, and older adults.30

Dehydration has been linked with dementia in older adults. In one study involving 1,091 male and female participants aged 65 to 97, those with dementia were significantly more likely to be dehydrated, as determined by serum osmolality levels, than controls. Moreover, those with Alzheimer’s disease had the highest dehydration risk. More severe cognitive impairment was found in the dehydrated participants with Alzheimer’s and vascular dementia than in those who were more hydrated.31 While further research is needed to determine whether this association is causal, some studies have found that additional fluid intake reduced the risk of confusion in older nursing home residents.6,16,31

Fluid losses of more than 1% of body mass have been associated in some studies with more negative emotions such as anger, hostility, confusion, depression, tension, and fatigue in adults, but other research has found no impact of hydration status on mood.6,14,30 At fluid losses of 2% or more of body mass, multiple studies have found impaired cognitive function, particularly for tasks associated with attention, executive functioning, arithmetic ability, working memory, short-term memory, decision making, motor coordination, fatigue, and alertness.6,14,32

One study of 40 military pilots noted their impaired performance in flight simulators when dehydrated to a fluid loss of at least 2% of body mass.33 Higher-order functions such as those involving attention, executive function, and motor coordination seem to be more vulnerable to the effects of dehydration, while less complex cognitive processes such as reaction time seem to be less sensitive. Some studies found improved responses on the tested cognitive tasks after participants were rehydrated, while others did not.14

Some research has found that increased water drinking in schoolchildren, compared with mild dehydration, was linked to improved results on tests of memory and attention, being more on task, and better reported mood, although some studies found no significant effects.14,30 One study of 230 adolescents in Malaysia found a significant link between hydration status, determined by urine color, and cognitive function as assessed by the Weschler intelligence scale for children.23 It’s been proposed that children are more vulnerable to the effects of dehydration on cognition than adults.14 Providing children with 10 to 16.8 oz of water per day in schools was found in some studies to improve their mood and cognitive performance.18

Although the mechanism for the impact of hydration status on cognition is unknown, theories include altered neurotransmitter levels (possibly via AVP levels), changed electrolyte levels, decreased blood flow to the brain, increased cortisol levels, and thirst distracting from other tasks.23,34,35

Chronic Disease and AVP Levels
Epidemiologic evidence has linked chronically elevated AVP levels to several chronic diseases, including CVD, stroke, hypertension, kidney disease, obesity, metabolic syndrome, diabetes, and cancer, possibly due to AVP’s effect on stress hormones and stimulation of hepatic gluconeogenesis and glycogenolysis.8,10,36

A water intake of 1.8 L or less per day seems to signal the brain to release AVP to conserve water. Chronically low volume drinkers can have elevated AVP with normal plasma osmolarity and body water levels. Researchers suggest that aspects of the typical Western diet, including excess animal protein and salt and insufficient high-water foods such as fruits and vegetables, may contribute to lower fluid intake and elevated AVP levels.10 They recommend increasing fluid consumption to more than 1.8 L per day, with some recommending up to 2.5 to 3.5 L per day, as a way to lower circulating AVP levels.10,36

Many other factors impact AVP levels, and, while increasing fluid intake has been shown to lower elevated AVP levels, it’s unclear whether the links between AVP and chronic disease are causal and whether reducing AVP levels will lower disease risk.10,36,37

Cardiovascular System
Dehydration decreases cardiac output proportionally and, particularly when moderate or severe, or combined with exercise, heat stress, or diuretic use, has been shown to impair vascular and endothelial function and blood pressure regulation.6 Dehydration also has been linked with elevated whole blood and plasma viscosity, which are risk factors for several cardiac conditions, including myocardial infarction, deep vein thrombosis, and possibly stroke.16 Chronic low fluid intake has been associated observationally with congestive heart failure and mitral valve prolapse, which has been reversed with rehydration, and deep vein thrombosis.6,15,16 There are case reports of cardiorespiratory arrest occurring with dehydration and exercise in the heat.6 The majority of studies on dehydration and cardiovascular function are noted to have been done in men.26

Dehydration appears to worsen outcomes in patients hospitalized for cardiovascular conditions. Patients with acute coronary syndrome with lower fluid balance, as measured by hyperosmolarity, were found to have longer lengths of stay and worse outcomes, including increased risk of sudden death. Patients hospitalized for stroke have a high prevalence of dehydration, and development or worsening of dehydration during hospitalization for ischemic stroke has been associated with poorer patient outcomes.15

NHANES data from 2009–2012 for adults aged 18 to 64 showed that inadequate hydration, defined by 800 mOsm/kg or higher urine osmolality, was significantly associated with higher BMI and obesity, defined by BMI of 30 or above.19 Adults with obesity have been found to have more concentrated urine on average, and higher levels of dehydration than adults without obesity.21 Limited data suggest that, in some people with obesity, increasing fluid intake before or during meals may enhance weight loss.16

Urinary System
Some studies have shown prevention of both primary and recurrent urinary tract infections (UTIs) in children and adults with increased fluid intake, and some expert organizations therefore recommend increasing fluid intake in patients with UTIs.6,16 Researchers have recommended intake of 2.5 to 3.5 L of water per day for optimal hydration, to allow production of 2 to 3 L of dilute urine, with a goal osmolality of 500 mOsm/kg, to decrease UTI incidence.36

Research in both human and animal studies has found a decreased risk of bladder cancer with fluid intake of 2.5 L per day vs 1.3 L per day, mainly in men, though other studies haven’t found this link.6,16

There’s evidence from multiple studies that increasing hydration also prevents recurrent kidney stones. In addition, some observational studies suggest that fluid intake lowers primary kidney stone risk, including the consideration that more kidney stones occur in hot climates and during the summer months.6,8,16 It’s thought that additional fluids help by lowering urine concentration, which reduces crystal formation, and by increasing flushing of the urinary system. Recommendations from American and European urological associations are production of 2 to 2.5 or 3 L of urine per day to reduce stone formation.16,36

Dehydration also negatively impacts kidney function. It’s a significant risk factor for acute kidney failure, including in perioperative dehydration, but acute kidney failure generally is reversible.15,38 Heat-associated dehydration seems to be a major risk factor in epidemics of chronic kidney disease (CKD) in Central America, mainly among male agricultural workers working in the heat; physical work in the heat can lead to high sweat rates, causing fluid loss in workers.11,20,38 Observational studies suggest that increasing total water intake preserves kidney function and may prevent cyst growth in polycystic kidney disease.8 It’s thought that maintaining hydration may protect kidney function by reducing AVP levels. Increasing fluid intake to produce 3 L of urine per day is thought to protect against the development of CKD; sugary beverages should be avoided, however, as they may increase the risk of kidney disease.38 Once CKD is present, increasing urine volume may further impair renal function.16

Putting It Into Practice
Adequate water is critical for the human body to function and thrive. Despite the overall scarcity of research, dehydration and inadequate fluid intake have been shown to have negative effects on at least certain aspects of cognitive function, and far-reaching health effects, both acute and chronic, on a variety of body systems, which generally increase proportionally with decreasing body fluid levels.

Ensuring that clients and patients have access to adequate fluids is essential. Nutrition professionals have a role in advocating for preservation of safe drinking water sources and promoting equitable access to safe drinking water as a basic human right.

Counseling clients and patients and their families/caregivers, particularly those in vulnerable groups such as older adults and children, on optimal fluid intake and the risks of dehydration may lead to improved fluid status with associated cognitive and health benefits. Helping clients brainstorm ways to increase intake of healthful beverages, especially plain water, and high-water foods such as fruits and vegetables may help them to achieve hydration goals and improve or prevent health issues.

Hydration also should be a focus when working with athletes or individuals who do physical work in the heat, as they’re at higher risk of dehydration, especially those engaging in intense activities in hot weather. Recommendations for fluid intake and rehydration should be individualized to client needs.

Dietitians should assess hydration status when working with people who have chronic illnesses that impact fluid needs, long term care residents, or hospitalized patients, particularly critically ill individuals at high risk of dehydration, and they should work closely with physicians and other medical professionals to optimally address patients’ fluid needs.

— Sara Chatfield, MPH, RDN, LDN, is a Chicago-based freelance nutrition writer who has practiced dietetics in clinical and community settings.

Learning Objectives
After completing this continuing education course, nutrition professionals should be better able to:
1. Discuss the most essential functions of water in the body.
2. Counsel patients on several common causes of dehydration.
3. Distinguish various possible signs of dehydration.
4. Assess the effects of dehydration on cognition and other health systems.

CPE Monthly Examination

1. What fraction of body water is intracellular?
a. One-fourth
b. One-third
c. One-half
d. Two-thirds

2. Which of the following is a major risk factor worldwide for inadequate hydration and associated health risks?
a. Low levels of physical activity
b. High rates of obesity
c. Lack of access to safe drinking water
d. Lack of education on the risks of dehydration

3. Which of the following factors have been associated with a higher risk of dehydration in kids?
a. Higher intake of fruits and vegetables
b. Family income
c. Female sex
d. Higher levels of physical activity

4. Which of the following is one of several age-related changes that can increase the risk of dehydration in older adults?
a. Impaired thirst
b. Higher rate of water turnover
c. Increased activity level
d. Increased fluid needs

5. Hypotonic dehydration, when sodium losses exceed water losses, is commonly caused by which of the following?
a. Excessive sweating
b. Insufficient fluid intake
c. Diuretics
d. Acute renal failure

6. Which of the following two signs, when combined, were shown to warn of imminent dehydration in studies of older adults?
a. Dark urine and weight loss
b. Decreased skin elasticity and sunken eyes
c. Low urine output and tachycardia
d. Fatigue and missing drinks between meals

7. Cognitive impacts, especially on higher-order functions such as attention, executive function, and motor coordination, have been associated mainly with fluid losses greater than or equal to what percentage of body mass?
a. 1%
b. 2%
c. 3%
d. 5%

8. Researchers have recommended intake of 2.5 to 3.5 L of water per day to prevent which of the following conditions?
a. Urinary tract infections
b. Confusion
c. Stroke
d. Acute coronary syndrome

9. The hormone arginine vasopressin appears to be released when daily water intake is at or below what volume?
a. 1.5 L
b. 1.8 L
c. 2.5 L
d. 3.5 L

10. To reduce the risk of urinary problems, researchers and urological associations have recommended increasing hydration to produce what volume of urine?
a. 500 mL to 1 L
b. 1 to 2 L
c. 2 to 3 L
d. 4 to 6 L

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2. Rush EC. Water: neglected, unappreciated and under researched. Eur J Clin Nutr. 2013;67(5):492-495.

3. Hooper L, Bunn D, Jimoh FO, Fairweather-Tait SJ. Water-loss dehydration and aging. Mech Ageing Dev. 2014;136-137:50-58.

4. Rose JB. Water, sanitation, and the millennium development goals: a report card on global progress. Water Quality & Health Council website. https://waterandhealth.org/safe-drinking-water/drinking-water/water-sanitation-millennium-development-goals-report-card-global-progress/. Published July 10, 2015. Accessed July 23, 2021.

5. Drinking-water. World Health Organization website. https://www.who.int/news-room/fact-sheets/detail/drinking-water. Published June 14, 2019. Accessed July 23, 2021.

6. Dietary Reference Intakes for water, potassium, sodium, chloride and sulfate. The National Academies of Sciences, Engineering, and Medicine website. https://www.nap.edu/read/10925/chapter/1. Published 2005. Accessed July 23, 2021.

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10. Armstrong LE, Muñoz CX, Armstrong EM. Distinguishing low and high water consumers — a paradigm of disease risk. Nutrients. 2020;12(3):858.

11. Kenefick RW, Cheuvront SN. Hydration for recreational sport and physical activity. Nutr Rev. 2012;70 Suppl 2:S137-S142.

12. Manz F, Johner SA, Wentz A, Boeing H, Remer T. Water balance throughout the adult life span in a German population. Br J Nutr. 2012;107(11):1673-1681.

13. Dorfman L. Nutrition in exercise and sports performance. In: Mahan LK, Raymond JL, Krause’s Food & The Nutrition Care Process. 14th ed. St. Louis, MO: Elsevier; 2017:426-455.

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