Water and Minerals: Functions, Balance, and Key Nutrients

Water and Minerals

Overview

This section covers the essential roles of water and minerals in human nutrition, focusing on their physiological functions, balance, and the health implications of deficiencies and excesses. Key minerals discussed include calcium, phosphorus, sodium, potassium, iron, and fluoride.

Introduction to Minerals

Definition and Classification

• Minerals are inorganic elements essential for various bodily functions, comprising about 5 lbs of total body weight.

• Approximately 75% of body mineral content is calcium and phosphorus.

• Major minerals (macrominerals): Required in amounts >100 mg/day (e.g., calcium, phosphorus, magnesium, sodium, potassium, chloride, sulfate).

• Trace minerals (microminerals): Required in amounts <100 mg/day (e.g., iron, fluoride, iodine, zinc, selenium, chromium, copper, manganese, molybdenum).

Shortfall nutrients in the US: calcium, potassium, magnesium, iron. Most overconsumed mineral: sodium.

Roles in the body: Form parts of salts, bones, and teeth; act as cofactors for enzymes.

Major and Trace Minerals

Major Minerals (Macrominerals)

• Needed in amounts >100 mg/day.

• Include: calcium, phosphorus, magnesium, sodium, potassium, chloride, sulfate.

Trace Minerals (Microminerals)

• Needed in amounts <100 mg/day.

• Include: iodine, iron, zinc, selenium, fluoride, chromium, copper, manganese, molybdenum.

Mineral Content in the Human Body

Mineral	Amount (g) in 60-kg Person
Calcium	1,150
Phosphorus	600
Potassium	210
Sulfur	140
Sodium	90
Chloride	90
Magnesium	30
Iron	4
Zinc	2.3
Copper	0.08
Manganese	0.02
Iodine	0.02
Selenium	0.015

Vitamin and Mineral Functional Groups

Antioxidants

• Key antioxidant vitamins: Beta-carotene, vitamin E, vitamin C.

• Key antioxidant mineral: Selenium.

• Many antioxidant phytochemicals also contribute.

Bone Health

• Key vitamins: D, K, C.

• Key minerals: calcium, phosphorus, magnesium, fluoride.

• Key energy nutrient: protein.

Energy Metabolism

• Key vitamins: thiamin, riboflavin, niacin, folate, B12, B6, biotin, pantothenic acid.

• Key minerals: iodine, iron, magnesium, zinc, selenium, copper, chromium, manganese, sulfur, molybdenum.

• Other nutrient: water.

Water

Functions and Distribution

• Most indispensable nutrient; makes up about 60% of adult body weight.

• Found in cardiovascular and lymphatic systems, soft tissues, and bones.

• Brain and muscle: 75–80% water; bones: 25% water.

Why Water Is Indispensable

• Carries nutrients throughout the body.

• Solvent for minerals, vitamins, amino acids, glucose, and other small molecules.

• Participates in chemical reactions.

• Cleanses tissues and blood of wastes.

• Acts as a lubricant and shock absorber around joints and organs.

• Primary component of amniotic fluid.

• Helps regulate body temperature.

Water Balance

Definition and Importance

• Water balance is the equilibrium between water intake and output, maintained rapidly by the body.

• Dehydration: Not enough water; can be fatal. Early signs include thirst, headache, confusion, fatigue, and increased heart rate.

• Water intoxication: Excess water dilutes electrolytes; rare but can be fatal if several gallons are consumed in a few hours.

• Body water can fluctuate by several pounds due to factors like menstruation or high salt intake.

Thirst and the Hypothalamus

• Thirst and satiety regulate water intake.

• The hypothalamus signals the pituitary gland, which instructs the kidneys to retain or release water via urine.

• Caffeine acts as a mild diuretic but does not significantly affect hydration status.

Effects of Dehydration and Chronic Low Fluid Intake

Mild Dehydration (Loss < 5% Body Weight)	Severe Dehydration (Loss > 5% Body Weight)	Chronic Low Fluid Intake May Increase the Likelihood of:
Thirst	Pale or shriveled skin	Heart attack and other heart problems
Sudden weight loss	Bluish lips and fingertips	Constipation
Dry, cool skin	Confusion; disorientation	Dental disease
Dry mouth, throat, body linings	Rapid, shallow breathing	Gallstones
Rapid pulse; low blood pressure	Weak, rapid, irregular pulse	Glaucoma (elevated eye pressure)
Lack of energy; weakness; headache	Thickening of blood	Hypertension; stroke
Impaired kidney function	Scant urine; brown-colored urine	UTIs; kidney stones
Reduced quantity of dark yellow or amber-colored urine	Shock; seizures; DEATH	Pregnancy/childbirth problems

Water Needs and Fluid Intake

How Much Water Is Needed?

• Needs vary based on food, air temperature, altitude, humidity, and physical activity.

• Daily fluid needs are met through beverages, water in food, and water produced by metabolism.

• DRI recommendations: Males: 13 cups (3 1/4 quarts)/day; Females: 9 cups (2 1/4 quarts)/day (includes all fluids and water from food).

Factors Increasing Fluid Needs

• Alcohol consumption, cold weather, dietary fiber, diseases affecting water balance (e.g., diabetes, kidney disease), forced-air environments, heated environments, high altitude, hot/humid weather, increased protein/salt/sugar intake, ketosis, medications (diuretics), physical activity, pregnancy/breastfeeding, prolonged diarrhea/vomiting/fever, surgery, blood loss, burns, very young or old age.

Water Content of Foods and Beverages

Percentage	Foods and Beverages
100%	Water, diet soft drinks, seltzer (unflavored), plain tea
95–99%	Sugar-free gelatin dessert, clear broth, Chinese cabbage, celery, cucumber, lettuce, summer squash, black coffee
90–94%	Sports drinks, grapefruit, fresh strawberries, broccoli, tomatoes
80–89%	Sugar-sweetened soft drinks, milk, yogurt, egg white, fruit juices, low-fat cottage cheese, cooked oatmeal, fresh apple, carrot
60–79%	Low-calorie mayonnaise, instant pudding, banana, shrimp, lean steak, pork chop, baked potato, cooked rice
40–59%	Diet margarine, sausage, chicken, macaroni and cheese
20–39%	Bread, cake, cheddar cheese, bagel
10–19%	Butter, margarine, regular mayonnaise
5–9%	Peanut butter, popcorn
1–4%	Ready-to-eat cereals, pretzels
0%	Cooking oils, meat fats, shortening, white sugar

Water Input and Output

• Input: Foods (700–1,000 ml), liquids (550–1,500 ml), water from metabolism (200–300 ml).

• Output: Kidneys (500–1,400 ml), skin (450–900 ml), lungs (350 ml), feces (150 ml).

• Total daily input and output: 1,450–2,800 ml.

Body Fluids and Minerals

Electrolytes and Water Movement

• Fluids cannot move freely in and out of cells, but minerals can be pumped in and out.

• Major minerals form salts that dissolve in body fluids (e.g., sodium outside cells, potassium inside cells).

• Electrolytes: Electrically charged dissolved mineral ions that attract water; water moves toward higher electrolyte concentration.

• Key electrolytes in sports drinks: sodium chloride (NaCl), potassium chloride (KCl).

How Electrolytes Govern Water Flow

• Water moves across cell membranes to balance the concentration of dissolved particles (osmosis).

• When one side of a membrane has more dissolved particles, water moves toward that side until concentrations are equal.

Electrolyte Imbalances

Fluid and Electrolyte Balance

• Essential for survival; rapid shifts can cause medical emergencies.

• Prolonged diarrhea or vomiting can cause fluid loss from digestive tract, pulling water from cells throughout the body.

• The kidneys respond by conserving water and adjusting sodium concentration, which can further disrupt balance and cause irregular heartbeat or fatalities.

Acid-Base Balance

Role of Minerals

• Minerals help regulate acid-base balance (pH) in the body.

• When dissolved in water, some minerals form acids (release H+ ions) or bases (release OH- ions).

• Maintaining a constant pH (blood pH = 7.35–7.45) is essential for life.

• Buffers: Molecules (including some minerals and proteins) that help maintain pH by absorbing or releasing H+ ions.

• Lungs also help regulate pH by excreting CO2.

Equation for pH: $\text{pH} = -\log_{10}[\text{H}^+]$

Sodium (Na)

Functions and Recommendations

• Principal cation outside cells; combines with chloride to form table salt (NaCl).

• Roles: fluid and electrolyte balance, acid-base balance, nerve and muscle function (with potassium).

• Deficiency (hyponatremia): too little sodium in the blood.

• Excess sodium is excreted if water intake is sufficient.

Recommendations

• Intake: 1,500 mg/day (healthy adults), 1,300 mg/day (ages 51–70), 1,200 mg/day (elderly).

• UL (Tolerable Upper Intake Level): 2,300 mg/day (about 1 tsp table salt).

• High sodium intake is linked to hypertension, heart disease, kidney problems, and stroke; about 40% of Americans are salt-sensitive.

Chloride (Cl)

Functions

• Helps maintain fluid balance.

• Part of hydrochloric acid (HCl) in the stomach, necessary for protein digestion.

• Food source: table salt (NaCl).

Potassium (K)

Functions, Deficiency, and Toxicity

• Principal cation inside cells; maintains fluid and electrolyte balance and cell integrity.

• Signals nerve impulses with sodium exchange across cell membranes; aids muscle contraction, including a steady heartbeat.

• Deficiency: Loss from inside cells (e.g., dehydration, fasting, eating disorders, severe diarrhea) can cause muscle weakness, paralysis, confusion, and even sudden death.

• Toxicity: Excess from foods is safe, but rapid IV administration or overdose of supplements can stop the heart.

Potassium Snapshot

• DRI for adults: 4,700 mg/day.

• Roles: Maintains normal fluid and electrolyte balance, supports cell integrity, assists in nerve functioning and muscle contractions.

• Deficiency: Muscle weakness, paralysis, confusion.

• Toxicity: Muscle weakness, vomiting, cardiac arrest (in cases of overdose or IV administration).

Foods High in Potassium

• Baked potatoes, avocados, bananas, oranges, lima beans, butternut squash, wild salmon, baked potatoes, artichokes, spinach, tomatoes, and dairy products.

Additional info: Other high-potassium foods include leafy greens, beans, nuts, and dairy products.