Minerals Notes

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Lecture Information

• Subject: Minerals
• Lecture: 9
• Field: Nutrition, Physiology & Biochemistry
• Institution: Sheffield Hallam University

Learning Outcomes

By the end of this session, participants will be able to:

• Define minerals and summarize their importance.
• Describe the main dietary sources, functions, signs of toxicity, and signs of deficiency of both iron and calcium.

Overview of Minerals

• Definition:
  • Minerals are inorganic elements found in nature.
  • They are present in soil and integrated into the growth of plants.
  • Humans obtain minerals through the consumption of plants and animals as well as from drinking water.
  • They are excreted from the body via urine, sweat, and feces, necessitating regular dietary replenishment.
• Essential Minerals:
  • The exact number of essential minerals for human life is not definitively known but is estimated to be between 18 and 20.
  • There are two categories of minerals:
  • Macro minerals: Required in larger amounts (e.g., calcium, phosphorus, sodium, potassium).
  • Trace elements: Needed in smaller amounts (e.g., iodine, copper, manganese).
• Issues related to assessing mineral status and interactions with other nutrients have hindered a comprehensive understanding.

Functions of Minerals

1. Growth and Development:
   • Calcium and phosphorus are primary components of bones.
2. Metabolic Regulation:
   • Many minerals are components of metalloenzymes, such as cytochrome enzymes involved in ATP production in the electron transport chain.
   • Minerals are crucial for blood clotting, muscle contraction, nerve impulses, and antioxidant activities.
3. Energy:
   • Like vitamins, minerals do not provide energy directly.

Overview of Key Minerals

Detailed Functions of Individual Minerals

Sodium (Na)

• Functions:
  • Maintains fluid balance and nerve signaling.
• Dietary Sources:
  • Major sources include breads, processed foods, and table salt.
• Deficiency: Uncommon.
• Toxicity: Can lead to cardiovascular disease and gastric cancer.

Potassium (K)

• Functions:
  • Critical for maintaining fluid balance and neuronal signaling.
• Dietary Sources:
  • Found in bananas, milk, and orange juice.
• Deficiency: Can result in cardiac arrest.
• Toxicity: Rare but serious.

Magnesium (Mg)

• Functions:
  • Acts as a cofactor in numerous enzymes.
• Dietary Sources:
  • Green leafy vegetables, seeds, and whole grains.
• Deficiency: Can cause neuromuscular dysfunction.
• Toxicity: Rare.

Copper (Cu)

• Functions:
  • Serves as a cofactor in several enzymes.
• Dietary Sources:
  • Shellfish, sesame seeds, potatoes.
• Deficiency: Can lead to neutropenia, bone fractures, and anemia.
• Toxicity: Rare.

Zinc (Zn)

• Functions:
  • Acts as a cofactor in a variety of enzymes, essential for processes like DNA synthesis and immune function.
• Dietary Sources:
  • Whole grains, poultry, beans.
• Deficiency: Affects 1/3 of the global population; can impair growth, cause fatigue, and neuropsychiatric issues.
• Toxicity: Can result in nausea, vomiting, and fever; chronic high doses impair copper utilization and calcium absorption.

Phosphorus (P)

• Functions:
  • Vital for bone composition, DNA structure, cellular metabolism, and membrane integrity.
• Dietary Sources:
  • Lentils, meat, dairy products.
• Deficiency: Leads to appetite loss, fatigue, and muscle weakness.
• Toxicity: Can cause gastrointestinal distress.

Selenium (Se)

• Functions:
  • Acts as a cofactor for enzymes and provides antioxidant functions while supporting reproductive health.
• Dietary Sources:
  • Fish and Brazil nuts.
• Deficiency: Impacts immune function.
• Toxicity: May lead to selenosis characterized by brittle nails, skin lesions.

Chlorine (Cl)

• Functions:
  • Important for fluid balance and a component of stomach acid.
• Dietary Sources:
  • Widely found in many foods including breads and processed foods.

Iodine (I)

• Functions:
  • Essential for the production of thyroid hormones.
• Dietary Sources:
  • Predominantly obtained through milk and seafood (especially seaweeds).
• Deficiency: Can cause goitre and pressure on the windpipe.

Iron

General Information on Iron

• Symbol: Fe
• Classification: Transition metal, exists in both oxidized (Fe3+) and reduced (Fe2+) states.
• Dietary Sources:
  • Includes liver (to be avoided in pregnancy), red meats, poultry, eggs, seafood (e.g., salmon, tuna), beans, tofu, nuts, certain fruits, spinach, and fortified products.

Iron Types: Haem and Non-Haem Iron

• Haem Iron:
  • Accounts for 10-15% of dietary iron intake but contributes approximately 40% or more of total iron absorbed.
  • Found primarily in animal sources.
• Non-Haem Iron:
  • Derived from plant sources and needs to be converted to Fe2+ for absorption.

Iron Requirements by Age Group (in mg/day)

Functional Roles of Iron

• Key Functions:
  • Integral part of hemoglobin, facilitating oxygen transport in the body.
  • Component of myoglobin, aiding oxygen diffusion into muscle cells.
  • Involved in electron transport chain proteins and essential metalloenzymes important for energy metabolism.
  • Supports red blood cell production and immune functions, assists in thyroid hormone metabolism.

Iron Absorption Mechanism

• Location: Predominantly occurs in the duodenum.
• Transport Mechanisms:
  • Haem and non-haem iron utilize different transport proteins on mucosal cells (HCP1 & DMT1).
  • Haem iron is absorbed intact, released by heme oxygenase.
  • Non-haem iron requires reduction from Fe3+ to Fe2+ for absorption facilitated by ferric reductase.
• Transportation in the Body:
  • Transferrin, produced in the liver, transports iron in the bloodstream following absorption.

Regulating Iron Absorption

• Iron Regulation Mechanism:
  • The body does not actively excrete excess iron; instead, absorption is tightly controlled.
  • Iron is reused (e.g., from red blood cells) and stored in reversible forms (e.g., ferritin and haemosiderin).
• Key Hormone - Hepcidin:
  • Regulates iron absorption and maintains iron balance in the body.
  • Produced in response to serum iron levels; higher levels increase hepcidin release.
  • Hepcidin binds to ferroportin, closing iron channels to prevent excess iron release into the bloodstream.

Factors Affecting Iron Absorption

Iron Transport

• Role of Transferrin:
  • Transferrin is synthesized in the liver and is responsible for transporting iron throughout the body.
  • Cells uptake iron from transferrin via transferrin receptors.

Iron Storage

• Ferritin:
  • Ferritin serves as the main storage protein for iron; it can store approximately 4,500 iron atoms within its structure.
• Storage Locations:
  • About 70% of the body’s iron is found in hemoglobin, with additional stores in ferritin and myoglobin.

Iron Deficiency Stages

• The progression to iron deficiency anemia occurs in three stages:
  1. Iron Depletion: Decrease in ferritin reflecting reduced stores; hemoglobin remains normal.
  2. Iron Deficiency: Continued decrease in ferritin, serum iron levels drop while hemoglobin remains unaffected.
  3. Iron Deficiency Anemia: Low ferritin and hemoglobin levels; insufficient iron for normal red blood cell production.

Effects of Iron Deficiency Anemia

• Functional impacts arise mainly from reduced levels of hemoglobin, myoglobin, and iron-containing enzymes.
• Can significantly affect immune responses.
• Common symptoms include fatigue, decreased work performance, and increased restlessness.

Potential Causes of Iron Deficiency

• Insufficient dietary intake (e.g., vegan or vegetarian diets).
• Blood loss (e.g., menstruation).
• Malabsorption (e.g., Coeliac disease).
• Increased physiological requirements (e.g., during growth spurts or pregnancy).
• Inflammatory conditions (e.g., inflammatory bowel disease).

Iron Overload

• Absorption Control: Once absorbed, the body lacks a mechanism for iron excretion.
• Acute Symptoms of Overload:
  • Abdominal pain, vomiting, metabolic acidosis, cardiovascular collapse.
• Chronic Overload Consequences:
  • Excess iron builds up in the liver and other organs if limits are exceeded, potentially leading to serious health issues such as liver cirrhosis and heart failure.
• Hereditary Hemochromatosis: An inherited condition where the body absorbs excess iron.
• Treatment Options:
  • Phlebotomy and chelation therapy to manage excess iron.

Calcium

General Information on Calcium

• Total Body Calcium Content: An adult has approximately 1 kg of calcium.
• Skeletal Component: About 99% of the body’s calcium is stored in bones.
• Other Essential Functions:
  • Involved in muscle contraction, hormonal responses, neurotransmitter release, and blood clotting enzyme functions.
• Plasma calcium levels (Ca2+) are tightly controlled.

Dietary Sources of Calcium

• In cases of deficiency, calcium is typically retrieved from the skeleton.
• Major Dietary Sources:
  • Dairy products (e.g., milk, cheese), green leafy vegetables (e.g., kale, spinach), fortified soya drinks, fish with bones (e.g., sardines).

Calcium Requirements by Age Group (in mg/day)

Calcium Absorption

• Typical Absorption Rates: Ranges from 10% to 30% in healthy adults with a mixed diet.
• Absorption Mechanisms:
  • Both saturable transcellular (using calcium transport proteins) and passive transport routes (paracellular).
• Factors Influencing Absorption:
  • Enhancers: Vitamin D, pregnancy, lactation.
  • Inhibitors: Phytates, oxalates, calcium or phosphorus deficiency, high or low habitual calcium intake.

Calcium Homeostasis

• Regulatory Hormones
  • Parathyroid Hormone (PTH): Released when plasma calcium is low to elevate levels; acts on bones and kidneys.
  • Calcitonin: Opposes PTH action, reducing plasma calcium.
  • 1,25 (OH)2D (Calcitriol): Enhances intestinal calcium absorption.

Calcium Deficiency

• Impact of Prolonged Deficiency:
  • Continuous calcium deficiency adversely affects bones as calcium is extracted to maintain plasma calcium levels.
• Consequences of Low Intake:
  • Insufficient intake during childhood or adolescence may inhibit peak bone mass development, increasing osteoporosis risk later.
  • Low intake in adulthood can lead to increased bone loss.

Calcium Toxicity

• Toxicity from calcium typically arises from excessive use of supplements.
• Common Issues Associated with Toxicity:
  • Formation of kidney stones, hypercalcemia, possible renal insufficiency, and impaired absorption of other