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Water and Minerals
Chapter 6
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Water
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Functions of water
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Occupies essentially every space within and between body cells
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Involved in virtually every body function
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Largest single constituent of the human body, averaging 60% of total body weight
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Provides shape and structure to cells
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Regulates body temperature
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Aids in the digestion and absorption of nutrients
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Water (cont’d)
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Functions of water (cont’d)
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Transports nutrients and oxygen to cells
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Serves as a solvent for vitamins, minerals, glucose, and amino acids
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Participates in metabolic reactions
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Eliminates waste products
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Is a major component of mucus and other lubricating fluids
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Water (cont’d)
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Water balance
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Total body water balance is tightly regulated within +/- 0.2% of body weight
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Sensation of thirst and the action of the hormone vasopressin control our daily fluid
balance
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Water output
 Adults lose approximately 1,750 to 3,000 mL of water daily
 Insensible water losses
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Water (cont’d)
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Water balance (cont’d)
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Water output (cont’d)
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Sensible water losses
Water intake
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Drinking water
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Other beverages
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Solid foods
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Water (cont’d)
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Water recommendations
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Body cannot produce as much water as it needs
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For men ages 19 to over 70, the adequate intake (AI) is 3.7 L/day
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For women of the same age, the AI is 2.7 L/day
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Daily intakes below the AI may not be harmful to healthy people
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Water (cont’d)
Water recommendations (cont’d)
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Osmoregulatory system
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Fluid intake is assumed to be adequate when the color of urine produced is pale yellow
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Elderly and children
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Drinking fluids should not be delayed until the sensation of thirst occurs
Water (cont’d)
Water recommendations (cont’d)
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Increases in water loss
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Vomiting, diarrhea, and fever
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Thermal injuries, fistulas, uncontrolled diabetes, hemorrhage, and certain renal
disorders
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Use of drainage tubes contributes to increased water losses
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Intake and output records are used to assess adequacy of intake
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Water (cont’d)
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Alterations in intake
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Dehydration is characterized by:
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Impaired mental function
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Impaired motor control
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Increased body temperature during exercise
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Increased resting heart rate when standing or lying down
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Increased risk of life-threatening heat stroke
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Water (cont’d)
Alterations in intake (cont’d)
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A net water loss of as little as 1% of body weight increases plasma osmolality
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A loss of 20% can be life-threatening
Hyponatremia
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At risk patients 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 or fail to replace lost sodium, or both
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Water (cont’d)
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Hyponatremia (cont’d)
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Symptoms
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Lung congestion, muscle weakness, lethargy, and confusion
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Can progress to convulsions, prolonged coma, and death
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Question
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Insensible water losses are those that cannot be measured. Insensible water losses occur
through what?
a. Urine
b. Feces
c. Respirations
d. Diaphoresis
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Answer
c. Respirations
Rationale: Extreme environmental temperatures (very hot or very cold), high altitude, low
humidity, and strenuous exercise increase insensible water losses from respirations and the skin.
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Keys to Understanding Minerals
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Major minerals are present in the body in amounts greater than 5 g
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Calcium, phosphorus, magnesium, sulfur, sodium, potassium, and chloride are major minerals
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Iron, iodine, zinc, selenium, copper, manganese, fluoride, chromium, and molybdenum are
classified as trace minerals or trace elements
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Both groups are essential for life
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Keys to Understanding Minerals (cont’d)
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General chemistry
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Minerals are inorganic elements that originate from the earth’s crust, not from plants or
animals
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Minerals do not undergo digestion, nor are they broken down or rearranged during
metabolism
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Minerals are not destroyed by light, air, heat, or acids during food preparation
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Keys to Understanding Minerals (cont’d)
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General functions
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Minerals function to provide structure to body tissues and to regulate body processes
Mineral balance
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Maintained by:
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Releasing minerals from storage for redistribution
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Altering rate of absorption
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Altering rate of excretion
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Keys to Understanding Minerals (cont’d)
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Mineral toxicities
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Stored minerals can produce toxicity symptoms
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Toxicity related to excessive use of mineral supplements, environmental or industrial
exposure, human errors in commercial food processing, or alterations in metabolism
Mineral interactions
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Mineral status must be viewed as a function of the total diet
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Keys to Understanding Minerals (cont’d)
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Sources of minerals
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Major electrolytes
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Unrefined or unprocessed foods have more minerals than refined foods
Sodium
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Salt (sodium chloride) is approximately 40% sodium
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Wide variations in sodium intake exist between cultures and between
individuals within a culture
Keys to Understanding Minerals (cont’d)
Major electrolytes (cont’d)
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Sodium (cont.)
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Major extracellular cation
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Largely responsible for regulating fluid balance
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Almost 98% of all sodium consumed is absorbed
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Adequate intake for sodium is set at 1,500 mg/ day
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100% of adult men and women exceed the AI of 1,500 mg of sodium/day
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Keys to Understanding Minerals (cont’d)
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Potassium
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Major cation of the intracellular fluid
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When potassium excretion is impaired, such as secondary to diabetes, chronic
renal insufficiency, end- stage renal disease, severe heart failure, and adrenal
insufficiency, high potassium intakes can lead to hyperkalemia and lifethreatening cardiac arrhythmias
Chloride
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Major anion in the extracellular fluid
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AI for younger adults is 2.3 g/day
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Question
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Is the following statement true or false?
Potassium is the major extracellular cation.
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Answer
False.
Rationale: Most of the body’s potassium is located in the cells as the major cation of the
intracellular fluid.
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Major Minerals
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Calcium
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Most plentiful mineral in the body
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Probably protects against colorectal cancer
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Calcium balance in the blood is achieved through the action of vitamin D and hormones
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3 daily servings of milk, yogurt, or cheese plus nondairy sources of calcium are needed
to ensure an adequate calcium intake
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An adequate calcium intake throughout the first 3 decades of life is needed to attain
peak bone mass as determined by genetics
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Major Minerals (cont’d)
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Phosphorus
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After calcium, the most abundant mineral in the body is phosphorus
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About 60% of natural phosphorus from food sources is absorbed
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Dietary deficiencies of phosphorus do not occur
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Magnesium
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4th most abundant mineral in the body
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Mean magnesium intake among American adults is approximately 80% of the RDA
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Major Minerals (cont’d)
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Sulfur
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Does not function independently as a nutrient but is a component of biotin, thiamin,
and the amino acids methionine and cysteine
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There is no RDA or AI for sulfur
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Trace Minerals
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Impact on health is significant
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Too little of a trace mineral can be just as deadly as too much
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Iron
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Approximately two-thirds of the body’s 3 to 5 g of iron is contained in the heme portion
of hemoglobin
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Iron in foods exists in two forms: heme iron found in meat, fish, and poultry, and
nonheme iron found in plants such as grains, vegetables, legumes, and nuts
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Overall rate of iron absorption is only 10% to 15% of total intake
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Trace Minerals (cont’d)
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Iron (cont’d)
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Only 1% to 7% of nonheme iron is absorbed from plant foods when they are consumed
as a single food
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RDA for iron is set at 8 mg for men and postmenopausal women, and at 18 mg for
premenopausal women
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Iron deficiency anemia
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Microcytic, hypochromic anemia
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Pica
Trace Minerals (cont’d)
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Iron (cont’d)
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Potential for toxicity is moderate to high
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Hemochromatosis
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Acute iron toxicity
Zinc
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A regular and sufficient intake is necessary
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Plays important roles in immune system functioning and in wound healing
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Trace Minerals (cont’d)
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Iodine
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Essential component of thyroxine (T4) and triiodothyronine (T3)
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Approximately 50% of the population uses iodized salt
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Goitrogens
Selenium
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A component of a group of enzymes that function as antioxidants
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Selenium deficiency is rare in the United States
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Trace Minerals (cont’d)
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Copper
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Distributed in muscles, liver, brain, bones, kidneys, and blood
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Involved in hemoglobin synthesis, collagen formation, wound healing, and maintenance
of nerve fibers
Manganese
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Dietary deficiencies have not been noted
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High manganese intake from drinking water also produces neuromotor deficits similar
to Parkinson’s disease
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Trace Minerals (cont’d)
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Fluoride
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Promotes the mineralization of developing tooth enamel prior to tooth eruption and the
remineralization of surface enamel in erupted teeth
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Fluoridation of municipal water
Chromium
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Enhances the action of the hormone insulin to help regulate blood glucose levels
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Appears that average intake is adequate
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Trace Minerals (cont’d)
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Molybdenum
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Plays a role in red blood cell synthesis
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Dietary deficiencies and toxicities are unknown
Other trace elements
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Evidence is difficult to obtain and quantifying human need is even more formidable
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Question
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Which major mineral is the most abundant in the human body?
a. Manganese
b. Selenium
c. Calcium
d. Sodium
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Answer
c. Calcium
Rationale: Calcium is the most plentiful mineral in the body, making up about half of the body’s
total mineral content.
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Water and Minerals in Health Promotion
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Water
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Recommended that thirst be the guide to consuming adequate fluid; specific amounts
or types of beverages to satisfy fluid need are not suggested
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For healthy people, hydration is unconsciously maintained with ad libitum access to
water
Sodium and potassium
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Recommendations:
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Less sodium
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More potassium