Water and several mineral elements are essential for maintenance of healthy oral tissues, including tooth enamel. Visual signs of these nutrient deficiencies in the gingiva, mucous membranes, and salivary glands are less obvious than signs observed with the B-vitamin complex and vitamin C deficiencies discussed in Chapters 9 and 11. Nevertheless, water and several minerals have a significant effect on integrity of the oral cavity and, ultimately, nutritional status. Oral problems associated with hyper states or hypo states of the minerals discussed in this chapter are slow to develop and may not be critical immediately. Chronically decreased salivary flow attributable to inadequate body fluids may lead to rampant tooth decay and eventually loss of teeth.
Water is the most abundant component in the body. At birth, water constitutes approximately 75% to 80% of body weight. Because such a large percentage of the infant’s body weight consists of water, fluid loss is more significant in infants than in adults. Total body water decreases with age, representing 50% to 60% of the total body weight of an adult. Adipose tissue contains less water than muscle; a person with a large amount of fat has a lower percentage of total body water. Women’s bodies, with inherently larger fat stores, contain less water than do men’s bodies, which have a higher percentage of lean muscle tissue.
Body fluids are distributed intracellularly and extracellularly. Intracellular fluid (ICF), which constitutes 60% of the body’s fluid weight, includes all the fluid within cells (chiefly in muscle tissue). Extracellular fluid (ECF) consists of fluid outside the cells. Fluid compartments are separated from one another by semipermeable membranes. These membranes serve as barriers by preventing movement of certain substances from one compartment to another; however, they do not completely isolate the compartments. Water is essentially unrestricted in its movement from compartment to compartment. Certain dissolved substances, or solutes, such as glucose, amino acids, and oxygen, also cross membranes freely. The cellular membranes allow maintenance of solute concentration by their selectivity.
When two compartments are separated by semipermeable membranes, and the movement of some solutes is restricted, osmosis occurs. Osmosis is the movement of water from an area of lower solute concentration to one of a higher solute concentration. Osmotic pressure within the body equalizes the solute concentration of ICFs and ECFs by shifting small amounts of water in the direction of higher concentration of solute, as shown in Chapter 3, Figure 3-6.
Water has several important physiological roles: (a) it acts as a solvent (fluid in which substances are dissolved), enabling chemical reactions to occur by entering into some reactions, such as hydrolysis; (b) it maintains stability of all body fluids, as principal component and medium for fluids (blood and lymph), secretions (saliva and gastrointestinal fluids), and excretions (urine and perspiration); (c) it enables transport of nutrients to cells and provides a medium for excretion of waste products; (d) it acts as a lubricant between cells to permit movement without friction; and (e) it regulates body temperature by evaporating as perspiration from skin and vapor from the mouth and nose. Negative fluid balance has serious detrimental effects on many physiological functions. A few days without water can be fatal.
Water requirements are based on experimentally-derived intake levels that are expected to meet nutritional needs of a healthy population. To maintain normal hydration, the Institute of Medicine (IOM) established an adequate intake (AI) for total fluid (beverages, water, and food). As shown in Table 12-1, men require 3.7 L/day (15 to 16 cups), and women require 2.7 L/day (11 to 12 cups). No tolerable upper intake level (UL) is established for water.
|Life Stage||Male (L/d)b||Female (L/d)b|
aAI (adequate intake)—the observed average or experimentally set intake by a defined population or subgroup that seems to sustain a defined nutritional status, such as growth rate, normal circulating nutrient values, or other functional indicators of health. An AI is used if insufficient scientific evidence is available to derive an estimated average requirement. For healthy human milk–fed infants, the AI is the mean intake. The AI is not equivalent to a recommended dietary allowance.
Data from Institute of Medicine (IOM), Food and Nutrition Board: Dietary reference intakes for water, potassium, sodium, chloride, chloride, and sulfate, Washington, DC, 2005, National Academies Press.
Overconsumption and underconsumption of fluids can occur over short periods. However, if adequate amounts of fluids are available, consumption matches physiological needs over an extended period. Loss of 1% of body water is usually compensated within 24 hours.1 Individuals who consume a high-protein or high-fiber diet, have diarrhea or vomiting, or are physically active or exposed to warm or hot weather, require more fluids.
Water is lost by a variety of routes: (a) urination, (b) perspiration, (c) expiration, and (d) defecation. Urine production depends on the amount of fluid intake and type of diet eaten. However, waste products must be kept in solution; minimum urine output to eliminate waste products is 400 to 600 mL/day.
Water losses in the form of sweat can vary greatly. An increase in body temperature (fever) is accompanied by increased sweating and respiration. Strenuous exercise can greatly affect the amount of water lost through the skin. Vapor in expired air varies with the rate of respiration. The presence of respiratory inflammation also elevates respiration rate. Approximately 100 to 200 mL of water is lost each day in feces; this is dramatically increased in individuals with diarrhea.
Water losses result in stimulation of water (thirst) and decreased kidney output to maintain fluid balance. Saliva also may help maintain water balance because saliva flow is reduced in dehydration, leading to drying of the mucosa and sensation of thirst.
Normal fluid requirements (Fig. 12-1) can be drastically changed in different climatic environments, with various exercise levels, diet, and social activities, and with illnesses resulting in (or are accompanied by) diarrhea or vomiting. The body cannot store water, so the amount lost must be replaced.
In healthy adults, thirst is an early sign of the body’s need for fluids, but is often mistaken for hunger. The ability to regulate water balance is not as precise in infants and older adults. Older patients often have a reduced sensation of thirst. When 2% of body water is lost, osmoreceptors are stimulated, creating a physiological desire to ingest liquids. Osmoreceptors are neurons in the hypothalamus that are sensitive to changes in serum osmolality levels. Stimulation of osmoreceptors not only causes thirst, but also increases release of antidiuretic hormone (ADH) from the pituitary gland (Fig. 12-2). ADH causes the body to retain fluid by decreasing urinary output. Conversely, if there is too much water in the body, ADH secretion is inhibited, and excess water is eliminated.
Decreased blood pressure also stimulates release of the enzyme renin, which ultimately leads to increased release of the hormone aldosterone by the adrenal cortex. This release of aldosterone results in retention of sodium and water by the kidneys, and excretion of potassium and hydrogen ions, causing blood pressure to increase.
Water is the only liquid nutrient that is essential for body hydration. During the process of metabolism, liquids and solid foods provide water. Some fruits and vegetables have a higher percentage of water than does milk, and meats are more than half water (Table 12-2). Regardless of its source, fluids act the same physiologically. Water liberated in the process of metabolism is also available. Metabolism of fat produces approximately twice as much water as the metabolism of protein or carbohydrate; metabolism of these macronutrients supplies about 300 to 350 mL daily.
|Food Item||% Water|
|Beer and wine||90-95|
|Milk, fruit juice, fruit drinks||85-90|
|Fruits (strawberries, melons, grapefruit, peaches, pears, oranges, apples, grapes, cucumbers, tomatoes)||80-85|
|Vegetables (lettuce, celery, cabbage, broccoli, onions, carrots)||80-85|
|Cottage cheese and yogurt||75-80|
|Liquid drinks for weight loss, muscle gain, meal replacement||70-85|
|Fish and seafood||70-80|
|Vegetables (potatoes, corn)||70-75|
|Rice and pasta||65-80|
|Stew, pasta and meat dishes, casseroles (with meat and meatless), meatloaf, tacos, enchiladas, macaroni and cheese||60-80|
|Sauces and gravies||50-85|
|Beef, chicken, lamb, pork, turkey, veal||45-65|
|Breads, bagels, biscuits||30-45|
|Ready-to-eat breakfast cereals||2-5|
|Chips, pretzels, candies, crackers, dried fruit, popcorn||1-5|
Adapted from Grandjean A, Campbell S: Hydration: fluids for life, Washington, DC, 2004, ILSI North America.
Plain tap water is the most natural source of fluids, best for quenching thirst, most economical, and healthiest. However, many Americans have become disenchanted with tap water. Although not perfect, the United States has one of the safest public water supplies in the world. During the past century, many improvements in Americans’ health can be attributed to improvements in drinking water, such as community fluoridation and controlling infectious diseases. When ground water becomes polluted, it is no longer safe to drink. Naturally occurring arsenic and radon in the environment can contaminate water. Some of the ways water can become contaminated is from use of fertilizers and pesticides, microbial contamination, and manufacturing processes. Drugs have been detected in drinking water of several major metropolitan areas. This contamination could be from medications not absorbed by individuals and eliminated through physiological discharges or numerous other reasons. Many pharmaceuticals pass through sewage and drinking water treatment plants. Some gastrointestinal illnesses occur from small or individual water systems.
The U.S. Environmental Protection Agency regulates levels of contaminants allowed in drinking water in public water systems. Water utility companies are required to provide Consumer Confidence Reports to their customers annually. Private well owners are responsible for ensuring their water is safe from contaminants of high concern. Wastewater is treated, but most treatments do not remove all drug residues and other contaminants. In some cases, contaminants are not monitored. Although present in very low amounts, the effect of these drugs and contaminants on health is unknown. The U.S. Environmental Protection Agency is continually looking at methods to detect and quantify pharmaceuticals and other contaminants in wastewater.
Because of mistrust of the water supply, and a desire for a safer and more convenient form of fluid intake, consumers frequently choose bottled water. The bottled water market has been increasing, with an annual per capita consumption of 11 gallons in 2011.2 However, as a result of environmental concerns (energy required to produce plastic nonbiodegradable plastic bottles, bisphenol A [BPA] content of bottles, cost of marketing and shipping bottles containing water), and the revelation that approximately 75% of reputable bottlers utilize groundwater (same source as the public water supply) or tap water, the rate of increase has declined.3
Bottled water is regulated by the U.S. Food and Drug Administration (FDA). Bottled waters come with many labels: drinking water, sparkling water, mineral water, Artesian water, and purified water (distilled, demineralized, deionized, and reverse osmosis). Bottled water also includes flavored waters and nutrient-added water beverages. In 2009, the FDA mandated that all manufacturers of bottled water test their water source for the presence of coliforms (a bacterial indicator of sanitation, universally present in the feces of animals) on a weekly basis. If further tests prove positive for Escherichia coli, companies must take measures to eliminate the bacteria and retest samples before use. The FDA also established the U.S. Environmental Protection Agency’s maximum levels for contaminants (except for a lower maximum amount of lead) and disinfection by-products (e.g., bromate, chlorite, etc.), and disinfectants (e.g., chlorine) in bottled water.4
This trend has resulted in increased water intake, but numerous problems are associated with this practice. Many consumers think bottled water is healthier, but most bottled waters do not contain fluoride. Fluoride does not have to be listed on the label unless it is added.
In addition to plain bottled water, manufacturers are adding other ingredients; many of these are nutrients. Supermarket shelves are filled with ready-to-serve coffees and teas, carbonated beverages, sports and energy drinks; vitamin water; and drinks containing amino acids, B vitamins, caffeine, green tea, vitamin C, ginger, cranberry extracts, or ginkgo (Ginkgo biloba). These drinks are often expensive.
Many of these flavored beverages contain additional kilocalories, which are consumed in excessive amounts by most Americans. Kilocalories in drinks are not hidden, and the body does not treat them differently from energy provided in foods. But kilocalories in beverages go down so smoothly, significant amounts can be consumed without realizing how much is being consumed. Studies have produced conflicting results as to whether or not people compensate for kilocaloric intake from sugar-sweetened beverages. Sugar-containing beverages are at least questionable for individuals needing to control their energy intake and weight.5,6
Water has been recommended for weight loss, despite the fact that fluids satisfy thirst and not hunger. Water consumed with a meal does not affect caloric consumption at mealtime, but water incorporated into food (as in soup) increases satiety, ultimately leading to less caloric intake. Basically, foods that incorporate water tend to appear larger; more volume provides greater oral stimulation; and water bound to food slows absorption and increases satiety.7
Although water is the only fluid truly needed by the body, many other liquids are acceptable, and some, such as low-fat milk, contribute significant amounts of important nutrients. Figure 12-3 depicts the beverage intake pattern of adults in the United States; beverages in these amounts and proportions represent almost 400 kcal daily. A recommended healthier intake would include at least 100 fl oz total intake with approximately 50% from water, approximately 16 oz of unsweetened tea or coffee, at least 8 oz low fat milk, approximately 24 oz of beverages with some kilocalories and nutrients (fruit juice), and approximately 12 oz of calorically sweetened and diet beverages.
For many Americans, coffee tastes good and helps “jump start” the morning. Coffee, without added sugars or creamers, contains negligible kilocalories. In addition to contributing to fluid intake, coffee has some health benefits. Coffee contains literally a thousand different substances, including healthful antioxidants. It is not a significant source of vitamins and minerals, but it does contain small amounts of magnesium, chromium, and potassium, nutrients many Americans are lacking.
Although research has not yet produced definite answers, a growing body of research suggests that moderate coffee drinkers, compared to nondrinkers, are less likely to have type 2 diabetes;8 Parkinson and Alzheimer disease;9,10 dementia;11 certain cancers (liver and prostate);12 heart failure;13 arrhythmia problems;14 and strokes.15 However, coffee has not been shown to prevent these conditions. A large prospective study found an inverse relationship between coffee consumption and total and cause-specific mortality, but this study was unable to determine whether this was a causal or associative finding.16 Both regular and decaffeinated coffee contain acids that may aggravate heartburn. Because of the addition of caffeine to many new products, the U.S. FDA is investigating the safety of caffeine.
Polyphenols in tea appear to possess health benefits, specifically antioxidant and anti-inflammatory actions as key mechanisms in preventing certain types of cancer, CHD, and diabetes.17-19 Teas also contain multiple flavonoids and have virtually no kilocalories unless sugar or milk are added. It is fairly well established that flavonoids in tea have health benefits, and tea may be a better alternative beverage to coffee, partly because of its lower caffeine content (Box 12-1). Highly processed tea leaves provide less polyphenols or flavonoids: oolong and black teas are oxidized or fermented, resulting in lower concentrations of polyphenols than green tea. Green tea has been more widely studied than other teas.
All green, black, and white teas contain caffeine and theanine (an amino acid used to treat anxiety and high blood pressure and other things). These chemicals affect the brain and appear to heighten mental alertness.20,21 Limited studies support the theories that compounds in tea may help encourage weight loss,22 lower cholesterol, and improve resistance to infections.23 One drawback to tea consumption is its tannin content, which inhibits iron absorption, particularly when tea and iron are consumed at the same time.
Herbal teas are made from herbs, fruits, seeds, or roots steeped in hot water. Although their chemical composition varies widely depending on the plant used, they have lower concentrations of antioxidants than green, white, black, and oolong teas. Research on health benefits (weight loss and resistance to infections) of herbal teas has been limited.
Most teas are benign, but the FDA has issued warnings regarding those that contain senna, aloe, buckthorn, and other plant-derived laxatives. The FDA has granted permission for unauthorized health claims for some teas and requested some manufacturers remove health claims on their labels.
Energy drinks were introduced in the United States in 1997. Sales of energy drinks and shots have more than doubled in the past 5 years; they are especially appealing to teenagers and young adults, especially young men. Sales in the United States increased to almost $9 billion in 2011.24 Energy drinks are marketed to provide a higher energy level, make a person feel more awake, and boost attention span.
Energy drinks contain ingredients that act as stimulants, such as caffeine, guarana (a seed containing four times as much caffeine as coffee beans), and taurine (an amino acid with antioxidant properties). Coffee-energy drinks blend coffee extract with milk, taurine, and ginseng (allegedly improves concentration and thinking, physical stamina, athletic endurance; causes abdominal pain and headaches). Energy shots (approximately 2 oz) contain the same stimulants as energy drinks but are more concentrated. Decaffeinated energy drinks have eliminated caffeine but are packed with B vitamins and quercetin (bioflavonoid reported to energize muscles). Whereas quercetin improved performance of mice on a treadmill, human studies failed to improve athletic performance.25 One popular liquid shot contains 8333% of the RDA for vitamin B12 and 2000% for vitamin B6, 150% for niacin, and 100% for folic acid.
Contrary to what commercial advertisements claim, B vitamins are not little packets of energy. Vitamins help the body use energy from foods, but extra B vitamins do not provide additional energy bursts. Almost all Americans get adequate amounts of B vitamins in their diets, yet marketers would lead people to believe that a megadose of B vitamins energizes. Energy drinks usually contain 140 kcal/8 oz from carbohydrates. These beverages may include some nutrients, but lack principal nutrients deficient in Americans’ diets.
Several of these energy drinks have been linked to unexpected deaths in apparently healthy adults and children, possibly leading to closer scrutiny and regulation by FDA. Energy drinks have contributed to increases in emergency department visits resulting from excessive caffeine intake especially when these drinks are combined with alcohol.26,27 Many in the medical community are concerned about potential negative problems associated with stimulants in beverages and lack of disclosure about the amount. Use of energy drinks may increase risk for caffeine overdose in caffeine abstainers, as well as habitual consumers of caffeinated coffee, soft drinks, and tea.
The amount of caffeine in a product is not required on labels because it is not a nutrient. If energy drinks contain “natural” ingredients, such as ginkgo or guarana, the FDA considers them a dietary supplement rather than a food or medication. One major corporation has recently decided to reclassify their energy-boosting products as a conventional food rather than a dietary substance because of what they call erroneous and misguided criticism. They have indicated they will include caffeine content on labels.
Recent emphasis on Americans increasing their physical activity appears to have sparked an interest in supplemental products by sports enthusiasts and people who are attempting to maintain their health. Sports nutrition products are now available in super markets and convenience stores in addition to their previous availability in gyms and health food stores.
Sports drinks and energy drinks are significantly different products, but the terms are confusing and used interchangeably by many consumers. Sports drinks (e.g., Gatorade and Powerade), popular among children and sports enthusiasts, are designed to restore fluid balance, to replace fluid and electrolytes lost in sweat during physical activity, and ultimately, to optimize athletic performance. Sports drinks often contain carbohydrates (a source of kilocalories), minerals (e.g., calcium and magnesium), electrolytes (e.g., sodium and potassium), and sometimes vitamins or other nutrients, such as protein and/or amino acids. Flavorings are added to enhance the taste. Protein in energy drinks has not been found to improve athletic performance, but protein enhances muscle recovery when ingested promptly after exercise. Specific amino acids added to sports drinks are reported to enhance immune function and enhance lipolysis; this claim has not been supported by clinical trials. There is no advantage to consuming vitamins and/or the minerals calcium and magnesium in sports drinks; these are readily available in a well-balanced diet.
Most research on sports products has been conducted using highly trained endurance athletes who exercise at high intensity for long periods. Sports nutrition recommendations are sometimes extrapolated to recreational athletes who have very different reasons for exercising, and therefore different nutritional needs. Most endurance athletes can benefit from a sports beverage that contains carbohydrates and electrolytes, and sometimes protein, but for most people engaged in routine physical activity, sports drinks offer little to no advantage over plain water. Sports drinks can be helpful for young athletes engaged in prolonged, vigorous physical activities; they are probably unnecessary during school physical education or in the school lunchroom. Sports drinks containing 6% to 8% carbohydrate are recommended when exercise is longer than 1 hour. These drinks can easily meet carbohydrate and fluid needs as well as sodium and potassium lost in sweat.28
Scientific studies do not support claims about improved performance and recovery for many sports drinks and protein shakes. Rather, researchers feel that it is virtually impossible for the public to make informed choices about the benefits and harms of advertised sports products.29
Beverages provide approximately 15% to 21% of Americans’ total daily kilocalories. Approximately 46% of 35- to 54-year olds say they drink at least one glass of soda daily as compared to 56% of 18- to 34-year olds reporting equivalent amounts.30 Approximately 20% of the U.S. population consumed diet sodas during 2009-2010.31 Soda consumption decreased among adolescents and young adults, whereas sports and energy drink consumption tripled among adolescents.32,33 Approximately half of the increase in energy intake occurring over the past 20 years is contributed to sweetened beverages. Most people are unaware of how many kilocalories are in the beverages they drink, but these kilocalories may be a major contributor to the alarming increase in obesity.
Most sports and energy drinks have a pH in the acidic range (pH 3 to 4) which is associated with enamel demineralization. The increase in use of sports and energy drinks by children and adolescents causes irreversible damage to teeth because high acidity levels (citric acid) in drinks erode tooth enamel. Damage to tooth enamel is evident after just 5 days of exposure to sports or energy drinks. Energy drinks cause twice as much damage to teeth as sports drinks.34 Calcium added to sports drinks lessens the erosive potential to teeth. Research suggests enamel erosion with various beverages occurs in the following order (from greatest to least): energy drinks, sports drinks, regular soda, and diet soda.35
Regulation of fluid intake and excretion by the kidneys usually maintain fluid balance in the body despite a wide range of intake. Imbalances may occur, however. Fluid volume excess (FVE) is the relatively equal gain of water and sodium in relation to their losses; fluid volume deficit (FVD) results from relatively equal losses of sodium and water.
FVE mainly occurs in ECF compartments secondary to an increase in total body sodium content (Fig. 12-4, C). Because water follows sodium, an excess of sodium leads to an increase in total body water. Excess fluid moves into interstitial compartments, located between cells and in body cavities such as joints, pleura, and gastrointestinal tract, causing edema.
Congestive heart failure, chronic renal failure, chronic liver disease, and high levels of steroids may predispose an individual to FVE because of sodium retention. Diseases causing a loss of protein and reduced serum albumin levels (e.g., malnutrition and renal diseases) may contribute to FVE because osmotic forces ordinarily exhibited by proteins and albumin are lacking. Common manifestations of FVE include rapid weight gain, puffy eyelids, distended neck veins, and elevated blood pressure. Peripheral edema is commonly observed in the legs and feet. Treatment involves correction of underlying problems, or therapy for the specific disease; fluid or sodium may be restricted (or both), or diuretics prescribed.
In FVD (Fig. 12-4, A), the sodium-to-water ratio remains relatively equal; ADH and aldosterone secretions are not activated. Prolonged inadequate fluid intake can result in FVD. However, FVD is usually associated with excessive loss of fluids from the gastrointestinal tract (vomiting, or diarrhea, drainage tubes), urinary tract (diuretics, polyuria, or excessive urination), or skin (sweating). Fever increases the need for electrolytes, increases fluid losses in dehumidified air (e.g., in an airplane), and causes diaphoresis (excessive sweating).
Dehydration temporarily leads to weight loss, but more importantly, adversely influences cognitive function and motor control.36 Decreased food and fluid intake can result from dementia, anorexia, nausea, or fatigue. Other, less obvious reasons are an inability to (a) obtain water, such as with impaired movement; (b) activate the thirst mechanism, as in hypodipsia (diminished thirst); or (c) swallow, as in neuromuscular problems or unconsciousness. Excessive fluid losses occasionally occur with prolonged exercise.
Common characteristics of FVD include weight loss, confusion and fatigue, sunken eyes, hypotension, and orthostatic hypotension. Classic signs are dry tongue with longitudinal fissures (slits or wrinkles that extend lengthwise on the tongue) (Fig. 12-5), xerostomia, shrinkage of oral mucous membranes, decreased skin turgor, dry skin, and decreased urinary output. A diminished salivary flow is associated with inadequate fluid intake. Pale yellow or almost colorless urine indicates adequate hydration. Dark yellow urine with a strong odor, advancing to painful urination, and (eventually) cessation of urine formation are progressive signs of inadequate water intake and dehydration. Treatment involves replacing lost fluid. If FVD is mild, oral fluids are likely to be sufficient. Intravenous solutions are needed with significant FVD.
Electrolytes are compounds or ions that dissociate in solution; they are also known as cations if they have a positive charge, and anions if they have a negative charge. Cations in the body include sodium, potassium, calcium, and magnesium; anions include chloride, bicarbonate, and phosphate. The body’s hydration status depends on an electrolyte balance of equal concentrations of cations to anions. Because the electrolyte concentration in plasma is so low, it is expressed as milliequivalents per liter (mEq/L). Electrolytes are important in water balance and acid–base (pH) balance.
Electrolyte distribution is different in ICF and ECF compartments. The principal cation in plasma and interstitial fluid is sodium; the principal anion is chloride. The principal cation in ICF is potassium; the principal anion is phosphate. The major difference between intravascular fluid and interstitial fluid is the large amount of protein in the former. Because sodium and potassium are the major cations, these are discussed in more detail.
The important physiological roles of sodium include (a) maintaining normal ECF concentration by affecting the concentration, excretion, and absorption of potassium and chloride, and water distribution; (b) regulating acid–base balance; and (c) facilitating impulse transmission in nerve and muscle fibers. Sodium is present in calcified structures in the body; its function in bones and teeth is unclear. It is also present in saliva. Sodium concentration in saliva determines one’s recognition of salt in food.
Because sodium is so readily available in foods, no RDA has been established. The IOM estimates a safe minimum intake might be 500 mg/day. This amount is increased in the face of abnormal losses. Sodium regulation involves several mechanisms. To keep the ECF concentration normal, the sodium-potassium pump is constantly moving sodium from the cell to ECF. Aldosterone released by the adrenal cortex results in sodium reabsorption or excretion by the kidneys depending on the body’s need (Fig. 12-6). The kidneys can adjust sodium excretion to match sodium intake despite large variations in intake. If serum sodium is high, aldosterone is inhibited, and sodium is excreted; the opposite is true for depressed serum sodium levels.
For most adults, the AI for sodium is 1500 mg/day with the UL being 2300 mg/day (Table 12-3). This AI does not apply to highly active individuals, such as endurance athletes, who lose large amounts of sodium through sweat.
|AI* for Sodium||UL† for Sodium||AI for Chloride||UL for Chloride|
|Life Stage||Male (g/day)||Female (g/day)||Male (g/day)||Female (g/day)||Male (g/day)||Female (g/day)||Male (g/day)||Female (g/day)|