Water and Minerals
Unfolding Case
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Myra Johnson
Myra is a healthy, active 83-year-old woman who is conscientious about healthy eating and exercise. She read about the many health benefits from using aloe to detox and decided to give it a try. Over a period of diligent use, she developed diarrhea but passed it off as part of the detox process. Her family took her to the emergency department when she exhibited what they thought were signs of a stroke: weakness, exhaustion, and delirium. What may be causing her symptoms?
Check Your Knowledge
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Learning Objectives
Upon completion of this chapter, you will be able to
1 Calculate a person’s fluid requirement.
2 Give examples of mechanisms by which the body maintains mineral homeostasis.
3 Identify sources of minerals.
4 Discuss functions of minerals.
5 Predict potential consequences of mineral deficiencies or toxicities.
6 Describe healthy eating patterns associated with optimal mineral intake.
Water is fundamental to life. It is the single largest constituent of the human body, averaging approximately 60% of the total body weight. It is the medium in which all biochemical reactions take place. Although most people can survive 6 weeks or longer without food, death occurs in a matter of days without water.
UNDERSTANDING WATER
Water occupies essentially every space within and between body cells and is involved in virtually every body function. Water
Provides shape and structure to cells. Approximately two-thirds of the body’s water is located within cells (intracellular fluid). Muscle cells have a higher concentration of water (70%-75%) than fat, which is only about 25% water. Men generally have more muscle mass than women and, therefore, have a higher percentage of body water.
Regulates body temperature. Because water absorbs heat slowly, the large amount of water contained in the body helps to maintain body temperature homeostasis despite fluctuations in environmental temperatures. Evaporation of water (sweat) from the skin cools the body.
Aids in the digestion and absorption of nutrients. Approximately 7 to 9 L of water is secreted in the gastrointestinal (GI) tract daily to aid in digestion and absorption. Except for the approximately 100 mL of water excreted through the feces, all of the water contained in the GI secretions (saliva, gastric secretions, bile, pancreatic secretions, and intestinal mucosal secretions) is reabsorbed in the ileum and colon.
Transports nutrients and oxygen to cells. By moistening the air sacs in the lungs, water allows oxygen to dissolve and move into blood for distribution throughout the body. Approximately 92% of blood plasma is water.
Serves as a solvent for vitamins, minerals, glucose, and amino acids. The solvating property of water is vital for health and survival.
Participates in metabolic reactions. For instance, water is used in the synthesis of hormones and enzymes.
Eliminates waste products. Water helps to excrete body wastes through urine, feces, and expirations.
Is a major component of mucus and other lubricating fluids. Water reduces friction in joints where bones, ligaments, and tendons come in contact with each other, and it cushions contacts between internal organs that slide over one another.
Water Balance
Water balance is the dynamic state between water output and water intake. Under normal conditions, output and intake are approximately equal (Fig. 6.1).
Water Output
On average, adults lose approximately 1750 to 3000 mL of water daily. Extreme environmental temperatures (very hot or very cold), high altitude, low humidity, and strenuous exercise increase
insensible water losses from respirations and the skin. Water evaporation from the skin is also increased by prolonged exposure to heated or recirculated air, for example, during long airplane flights. Sensible water losses from urine and feces make up the remaining water loss. Because the body needs to excrete a minimum of 500 mL of urine daily to rid itself of metabolic wastes, the minimum daily total fluid output is approximately 1500 mL. To maintain water balance, intake should approximate output.
insensible water losses from respirations and the skin. Water evaporation from the skin is also increased by prolonged exposure to heated or recirculated air, for example, during long airplane flights. Sensible water losses from urine and feces make up the remaining water loss. Because the body needs to excrete a minimum of 500 mL of urine daily to rid itself of metabolic wastes, the minimum daily total fluid output is approximately 1500 mL. To maintain water balance, intake should approximate output.
 Figure 6.1 ▶ Water balance approximations. |
Insensible Water Loss immeasurable losses.
Sensible Water Loss measurable losses.
Water Intake
Total water intake averages about 2.5 L/day, of which approximately 80% is from fluids and 20% from solid food (Institute of Medicine [IOM], 2005). Box 6.1 describes various types of bottled water. Except for oils, almost all foods contain water, with fruits and vegetables providing the most (Fig. 6.2). The body also produces a small amount of water from normal metabolism: The catabolism of carbohydrates, protein, and fat for energy yields carbon and hydrogen atoms that combine with oxygen to form water and carbon dioxide. On average, 250 to 350 mL of metabolic water is produced daily, depending on total calorie intake.
Metabolic Water water produced as a by-product from the breakdown of carbohydrates, protein, and fat for energy.
Water Recommendations
Water is an essential nutrient because the body cannot produce as much water as it needs. The Dietary Reference Intake (DRI) committee on fluid and electrolytes did not establish a Recommended Dietary Allowance (RDA) for water because of insufficient evidence linking a specific amount of water intake to health; actual requirements vary depending on diet, physical activity, environmental temperatures, and humidity.
The Adequate Intake (AI) for total water, which includes water from liquids and solids, is based on the median total water intake from U.S. food consumption survey data (IOM, 2005). For men age 19 years to older than 70 years, the AI is 3.7 L/day, which includes 3 L as fluids. For women of the same age, the AI is 2.7 L, which includes approximately 2.2 L from fluids. Similar to AIs set for other nutrients, daily intakes below the AI may not be harmful to healthy people because normal hydration is maintained over a wide range of intakes. Amounts higher than the AI are recommended for rigorous activity in hot climates. Because the body cannot store water, it should be consumed throughout the day.
BOX 6.1 U.S. Food and Drug Administration’s Standards of Identity for Common Types of Bottled Water
Artesian well water originates from a well that taps a confined aquifer and the water level must stand at some height above the top of the aquifer. An aquifer is an underground layer of rock or sand with water.
Mineral water contains at least 250 ppm total dissolved solids (minerals) that are naturally present, not added.
Purified water is produced by distillation, deionization, reverse osmosis, or other suitable processes to remove minerals and other solids. It may also be referred to as “distilled water” if it is produced by distillation, “deionized water” if it is produced by deionization, or “reverse osmosis water” if it was produced by reverse osmosis. Purified is not synonymous with “sterile.”
Sparkling water contains a “fizz” from carbon dioxide that was either present in the water when it emerged from its source or was present, removed in processing, and then replaced. Carbon dioxide levels cannot exceed the amount present in the original water. Sparkling water may be labeled as “sparkling drinking water,” “sparkling mineral water,” “sparkling spring water,” etc. Seltzer, tonic water, and club soda are carbonated beverages; they are not types of sparkling water.
Spring water comes from an underground source that flows naturally to the surface. It must be collected at the spring or through a bored hole that taps the spring underground.
Well water is collected with a mechanical pump from an underground aquifer.
Source: International Bottled Water Association. Bottled water. Available at http://www.bottledwater.org/content/faqs#2. Accessed on 2/27/16.
 Figure 6.2 ▶ Percentage of water content of various foods. |
The IOM did not specify how much of total fluid intake should come specifically from water. For healthy people, the universal, age-old advice has been to drink at least eight 8-oz glasses of water daily. Although that may be excellent advice, there is little scientific evidence to support this recommendation (Valtin, 2002). For healthy people, hydration is unconsciously maintained with ad lib access to water. In healthy adults, thirst is usually a reliable indicator of water need, and fluid intake is assumed to be adequate when the color of urine produced is pale yellow. In some conditions and for some segments of the population, the sensation of thirst is blunted and may not be a reliable indicator of need. For the elderly and children, and during hot weather or strenuous exercise, drinking fluids should not be delayed until the sensation of thirst occurs because by then fluid loss is significant.
Estimating Fluid Requirements
Box 6.2 outlines several methods for estimating fluid requirements. However, according to the American Dietetic Association’s Evidence Analysis Library, there are no validated equations for determining fluid needs nor is there evidence of a clinical or laboratory measure that best assesses hydration status (Academy of Nutrition and Dietetics, n.d.).
Inadequate Fluid Intake
An inadequate intake of water can lead to dehydration, characterized by impaired mental function, impaired motor control, increased body temperature during exercise, increased resting heart rate when standing or lying down, and an increased risk of life-threatening heat stroke. A net water loss of 1% to 2% of body weight causes thirst, fatigue, weakness, vague discomfort, and loss of appetite. A loss of 7% to 10% leads to dizziness, muscle spasticity, loss of balance, delirium, exhaustion, and collapse. Left untreated, dehydration ends in death.
Clinical situations in which water losses are increased—and thus water needs are elevated—include vomiting, diarrhea, fever, thermal injuries, uncontrolled diabetes, hemorrhage, certain renal disorders, and the use of drainage tubes. Intake and output records are used to assess adequacy of intake.
BOX 6.2 Methods to Estimate Fluid Needs
Method
Based on kg of body weight
30 mL/kg body weight for average adults Example: A 70-kg person needs 2100 mL/day (70 kg × 30 mL/kg = 2100 mL/day)
25 mL/kg for people with congestive heart failure or renal disease
35 mL/kg for people with infection or draining wound
Alternative method based on kg of body weight
Provide 1500 mL for the first 20 kg of weight and 15 mL/kg for each remaining kg. Example: A 70-kg person needs 2250 mL/day 1500 mL for the first 20 kg +750 mL (15 mL × 50 remaining kg) 2250 mL/day
Based on calories consumed
1 mL/cal consumed Example: A person consuming 2000 cal/day needs 2000 mL/day. (2000 cal/day × 1 mL/cal = 2000 mL/day)
Based on urine output
Urine output + 500 mL
Unfolding Case
Recall Myra. She lost excessive amounts of fluid from diarrhea and is diagnosed with dehydration. Why didn’t she feel thirsty as she became dehydrated?
Excessive Fluid Intake
A chronic high intake of water has not been shown to cause adverse effects in healthy people who consume a varied diet as long as intake approximates output (IOM, 2005). An excessive water intake may cause hyponatremia, but it is rare in healthy people who consume a typical diet. People most at risk include infants; psychiatric patients with excessive thirst; women who have undergone surgery using a uterine distention medium; and athletes in endurance events who drink too much water, fail to replace lost sodium, or both. Symptoms of hyponatremia include lung congestion, muscle weakness, lethargy, and confusion. Hyponatremia can progress to convulsions and prolonged coma. Death can result.
UNDERSTANDING MINERALS
Although minerals account for only about 4% of the body’s total weight, they are found in all body fluids and tissues. Calcium, phosphorus, magnesium, sulfur, sodium, potassium, and chloride are considered major minerals because they are present in the body in amounts greater than 5 g (the equivalent of 1 tsp). Iron, iodine, zinc, selenium, copper, manganese, fluoride, chromium, and molybdenum are classified as trace minerals, or trace elements, because they are present in the body in amounts less than 5 g, not because they are less important than major minerals. Both groups are essential for life. As many as 30 other potentially harmful minerals are present in the body, including lead, gold, and mercury. Their presence appears to be related to environmental contamination.
General Chemistry
Unlike the energy nutrients and vitamins, minerals are inorganic elements that originate from the earth’s crust, not from plants or animals. Minerals do not undergo digestion nor are they broken down or rearranged during metabolism. Although they combine with other elements to form salts (e.g., sodium chloride) or with organic compounds (e.g., iron in hemoglobin), they always retain their chemical identities.
Unlike vitamins, minerals are not destroyed by light, air, heat, or acids during food preparation. In fact, when food is completely burned, minerals are the ash that remains. Minerals are lost only when they leach from foods soaked in water.
Inorganic not containing carbon or concerning living things.
General Functions
Minerals function to provide structure to body tissues and to regulate body processes such as fluid balance, acid-base balance, nerve cell transmission, muscle contraction, and vitamin, enzyme, and hormonal activities (Table 6.1).
Mineral Balance
The body has several mechanisms by which it maintains mineral balance, depending on the mineral involved, such as
Releasing minerals from storage for redistribution. Some minerals can be released from storage and redistributed as needed, which is what happens when calcium is released from bones to restore normal serum calcium levels.
Altering rate of absorption. For example, normally only about 10% of the iron consumed is absorbed, but the rate increases to 50% when the body is deficient in iron.
Altering rate of excretion. Virtually all of the sodium consumed in the diet is absorbed. The only way the body can rid itself of excess sodium is to increase urinary sodium excretion. For most people, the higher the intake of sodium, the greater is the amount of sodium excreted in the urine. Excess potassium is also excreted in the urine.
Mineral Toxicities
Minerals that are easily excreted, such as sodium and potassium, do not accumulate to toxic levels in the body under normal circumstances. Stored minerals can produce toxicity symptoms when intake is excessive, but excessive intake is not likely to occur from eating a balanced diet.
Instead, mineral toxicity is related to excessive use of mineral supplements, environmental or industrial exposure, human errors in commercial food processing, or alterations in metabolism. For instance, in 2008, the most serious selenium toxicity outbreak that has ever occurred in the United States was caused by an improperly manufactured dietary supplement that contained 200 times the labeled concentration of selenium (Morris & Crane, 2013).
Instead, mineral toxicity is related to excessive use of mineral supplements, environmental or industrial exposure, human errors in commercial food processing, or alterations in metabolism. For instance, in 2008, the most serious selenium toxicity outbreak that has ever occurred in the United States was caused by an improperly manufactured dietary supplement that contained 200 times the labeled concentration of selenium (Morris & Crane, 2013).
Table 6.1 General Functions of Minerals | ||||||||||||
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 Figure 6.3 ▲ Key mineral contributions of MyPlate food groups. (Source: U.S. Department of Health and Human Services & U.S. Department of Agriculture. [2015]. 2015-2020 Dietary guidelines for Americans [8th ed.]. Available at http://health.govdietaryguidelines/2015. Accessed on 2/26/16.) |
Mineral Interactions
Mineral balance is influenced by hundreds of interactions that occur among minerals and between minerals and other dietary components. For instance, caffeine promotes calcium excretion, whereas vitamin D and lactose promote its absorption. Mineral status must be viewed as a function of the total diet, not just from the standpoint of the quantity consumed.
Sources of Minerals
Key minerals are found in all MyPlate food groups; items within each group vary in the amount and kind of minerals they provide (Fig. 6.3). Generally, unrefined or unprocessed foods have more minerals than refined foods. Trace mineral content varies with the content of soil from which the food originates. Within most food groups, processed foods are high in sodium and chloride. Drinking water contains varying amounts of calcium, magnesium, and other minerals; sodium is added to soften water. Fluoride may be a natural or added component of drinking water.
Mineral supplements, alone or combined with vitamins, contribute to mineral intake. As with vitamins, people who take mineral supplements have higher intakes of minerals from food than do people who do not take supplements (Bailey, Fulgoni, Keast, & Dwyer, 2011). With some minerals—namely, calcium, iron, zinc, and magnesium—supplements may contribute to potentially excessive intakes (Bailey et al., 2011).
MAJOR ELECTROLYTES
Sodium, chloride, and potassium are major minerals that are also major electrolytes in the body. Salient features for each electrolyte are presented in the following paragraphs. Table 6.2 details their recommended intakes, sources, functions, and signs and symptoms of deficiency and toxicity.
Sodium
By weight, salt (sodium chloride) is approximately 40% sodium; 1 tsp of salt (5 g) provides approximately 2300 mg of sodium. Box 6.3 describes various types of salt. It is estimated that approximately 75% of the sodium consumed in the typical American diet comes from salt or
sodium preservatives added to foods by food manufacturers. Only 12% of total sodium intake is from sodium that occurs naturally in foods such as milk, meat, poultry, vegetables, tap water, and bottled water (IOM, 2005). Salt added during cooking or at the table accounts for the remaining sodium intake. Figure 6.4 illustrates food category sources of sodium in the U.S. population. Wide variations in sodium intake exist between cultures and between individuals within a culture, based on the amount of processed foods consumed.
sodium preservatives added to foods by food manufacturers. Only 12% of total sodium intake is from sodium that occurs naturally in foods such as milk, meat, poultry, vegetables, tap water, and bottled water (IOM, 2005). Salt added during cooking or at the table accounts for the remaining sodium intake. Figure 6.4 illustrates food category sources of sodium in the U.S. population. Wide variations in sodium intake exist between cultures and between individuals within a culture, based on the amount of processed foods consumed.
Table 6.2 Summary of Major Electrolytes | ||||||||||||
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As the major extracellular cation, sodium is largely responsible for regulating fluid balance. It also regulates cell permeability and the movement of fluid, electrolytes, glucose, insulin, and amino acids. Sodium is pivotal in acid-base balance, nerve transmission, and muscular irritability. Although sodium plays vital roles, under normal conditions, the amount actually needed is very small, maybe even less than 200 mg/day.
Almost 98% of all sodium consumed is absorbed; yet, humans are able to maintain homeostasis over a wide range of intakes, largely through urinary excretion. A salty meal causes a transitory increase in serum sodium, which triggers thirst. Drinking fluids dilutes the sodium in the blood to normal concentration, even though the volume of both sodium and fluid are increased. The increased volume stimulates the kidneys to excrete more sodium and fluid together to restore normal blood volume. Conversely, low blood volume or low extracellular sodium stimulates the hormone aldosterone to increase sodium reabsorption by the kidneys. In people who have minimal sweat losses, sodium intake and sodium excretion are approximately equal.
Quick BiteExamples of sodium additives
To enhance flavor Sodium chloride Monosodium glutamate (MSG) Soy sauce Teriyaki sauce
To preserve freshness Brine Sodium sulfite (for dried fruits)
To prevent the growth of yeast and/or bacteria Sodium benzoate Sodium nitrate or sodium nitrite Sodium lactate Sodium diacetate
To prevent the growth of mold Sodium propionate
As an antioxidant Sodium erythorbate
As a sweetener Sodium saccharin
As a binder/thickener Sodium caprate Sodium caseinate
As a leavening agent Sodium bicarbonate (baking soda) Baking powder
As a stabilizer Sodium citrate Disodium phosphate
BOX 6.3 Types of Salt
Table salt is a fine-grained salt from salt mines that is refined until it is pure sodium chloride. It is mainly used in cooking and at the table and may or may not contain iodine. It often contains calcium silicate to keep it free flowing.
Kosher salt is a coarse-grain salt that does not contain any additives. It is used in the preparation of kosher meat according to Jewish dietary laws. Although the terms “kosher salt” and “sea salt” are often used interchangeably, kosher salt does not necessarily originate from the sea.
Sea salt may be fine or coarse grained. It has a slightly different flavor than table salt due to its mineral content. Although it is often promoted as a healthier alternative to table salt, the sodium content is essentially the same. The advantage is that people may use less sea salt than table salt because of its more pronounced flavor. Examples include Mediterranean sea salt, Alaea (Hawaiian) sea salt, and Black salt—salts named after the originating sea.
Pickling salt is a fine-grained salt used for making pickles and sauerkraut. It does not contain additives or anticlumping agents.
Specialty salts, such as popcorn salt, come in various grains and textures and are intended for specific purposes. Generally, table salt can be substituted for these salts.
Seasoned salt is a blend of salt, herbs, and other seasoning ingredients. Examples include celery salt, onion salt, and garlic salt. The actual sodium content is lower than table salt because other ingredients dilute the concentration of sodium.
Salt substitutes have some or all of the sodium replaced with another mineral, such as potassium or magnesium. They are also referred to as lite salt. They may have a bitter or metallic aftertaste.
Rock salt is a nonedible salt of large crystals used to deice driveways and walkways. When combined with regular ice in home ice-cream makers, it helps freeze homemade ice cream more quickly by absorbing heat.
 Figure 6.4 ▶ Food category sources of sodium in the U.S. population ages 2 years and older. (Source: U.S. Department of Health and Human Services & U.S. Department of Agriculture. [2015]. 2015-2020 Dietary guidelines for Americans [8th ed.]. Available at http://health. govdietaryguidelines/2015. Accessed on 2/22/16.) |
Unfolding Case
Think of Myra. The speed with which her food moved through the GI tract interfered with the absorption of fluid, electrolytes, and nutrients. She was given IV replacement fluid, an antidiarrheal medication, and oral fluids. What should Myra understand about the need for “detox” and its potential risks?
Mean sodium intake in the United States of males and females age 2 years and over exceeds recommended amounts (U.S. Department of Agriculture [USDA], Agricultural Research Service [ARS], 2014). In 2011 to 2012, mean intake of sodium among adult men and women age 20 years and older was 4218 and 2997 mg/day, respectively. These figures represent an increase over previous data reported in 2007 to 2008.
Potassium
Most of the body’s potassium is located in the cells as the major cation of the intracellular fluid. The remainder is in the extracellular fluid, where it works to maintain fluid balance, maintain acid-base balance, transmit nerve impulses, catalyze metabolic reactions, aid in carbohydrate metabolism and protein synthesis, and control skeletal muscle contractility.
Potassium is naturally present in most foods, such as fruits, vegetables, whole grains, meats, milk, and yogurt. Processed foods, such as cheeses, processed meats, breads, soups, fast foods, pastries, and sugary items, have a higher sodium-to-potassium ratio.
In healthy people with normal kidney function, a high intake of potassium does not lead to an elevated serum potassium concentration because the hormone aldosterone promotes urinary potassium excretion to keep serum levels within normal range. Therefore, an upper limit (UL) has not been set. However, when potassium excretion is impaired (e.g., secondary to diabetes, chronic kidney insufficiency, end-stage kidney disease, severe heart failure, or adrenal insufficiency), high potassium intakes can lead to hyperkalemia and life-threatening cardiac arrhythmias.
Quick BiteAverage potassium content by food group
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Chloride
Chloride is the major anion in the extracellular fluid, where it helps to maintain fluid and electrolyte balance in conjunction with sodium. Chloride is an essential component of hydrochloric acid in the stomach and, therefore, plays a role in digestion and acid-base balance. Its concentration in most cells is low.
Because almost all the chloride in the diet comes from salt (sodium chloride), the AI for chloride is set at a level equivalent (on a molar basis) to that of sodium. The AI for younger adults is 2.3 g/day, the equivalent to 3.8 g/day of salt or 1500 mg sodium. Sodium and chloride share dietary sources, conditions that cause them to become depleted in the body, and signs and symptoms of deficiency.
MAJOR MINERALS
The remaining major minerals are calcium, phosphorus, magnesium, and sulfur (summarized in Table 6.3); additional salient information appears in the following section.
Table 6.3 Summary of Major Minerals | |||||||||||||||
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CalciumCalcium is the most plentiful mineral in the body, making up about half of the body’s total mineral content. Almost all of the body’s calcium (99%) is found in bones and teeth, where it combines with phosphorus, magnesium, and other minerals to provide rigidity and structure. Bone tissue serves as a large, dynamic reservoir that releases calcium to maintain constant concentrations of calcium in blood, muscle, and intercellular fluids when dietary intake of calcium is inadequate. Continuous remodeling of bone occurs naturally throughout life as calcium is deposited and resorbed. The balance between bone formation and bone breakdown changes with aging. From birth through adolescence, bone formation exceeds bone breakdown. In young adults, the processes occur at approximately the same rate. Net bone loss occurs in all people after the age of about 30 years. Although an adequate calcium intake is needed to ensure bone mass is normally mineralized, an excess calcium does not lead to the creation of more bone; the amount of bone created is determined by the number and activity of osteoblasts (Reid, 2014). A dense bone mass offers protection against the inevitable net bone loss that occurs in all people after the age of about 35 years.
The remaining 1% of calcium in the body is found in plasma and other body fluids, where it has important roles in blood clotting, nerve transmission, muscle contraction and relaxation, cell membrane permeability, and the activation of certain enzymes. Calcium balance—or, more accurately, calcium balance in the blood—is achieved through the action of vitamin D and hormones. When blood calcium levels fall, the parathyroid gland secretes parathormone (PTH), which promotes calcium reabsorption in the kidneys and stimulates the release of calcium from bones. Vitamin D has the same effects on the kidneys and bones and additionally increases the absorption of calcium from the GI tract. Together, the actions of PTH and vitamin D restore low blood calcium levels to normal, even though bone calcium content may fall. A chronically low calcium intake compromises bone integrity without affecting blood calcium levels.
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