Major Minerals and Bone Health

Major Minerals and Bone Health

Minerals: Definition and Classification

Minerals are essential inorganic elements required by the body in small amounts to maintain structure and regulate chemical reactions and body processes. They are stable under heat, oxygen, and acid, and retain their identity even when combined with other elements.

• Major minerals: Needed in amounts greater than 100 mg/day (e.g., sodium, potassium, chloride, calcium, phosphorus, magnesium, sulfur).

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

Minerals in Our Food

The mineral content of food is influenced by several factors:

• Soil content: The amount of minerals in soil affects the mineral content of plants and, consequently, animal foods.

• Handling and processing: Minerals can be added or removed during food processing.

• Absorption and bioavailability: The presence of certain substances in plants (e.g., phytates, tannins, oxalates), other minerals, or the body's mineral status can inhibit absorption.

Mineral Bioavailability

Bioavailability refers to the proportion of a nutrient that is absorbed and utilized by the body.

• Some minerals, such as sodium, are almost completely absorbed (~100%), while others, like calcium, have much lower absorption rates (~5%).

• Ionic charge can affect absorption; minerals with similar charges (e.g., Ca2+, Mg2+, Zn2+, Cu2+) can compete for absorption.

• Phytates (in whole grains and legumes), tannins (in tea and some legumes), and oxalates (in spinach, rhubarb, and chocolate) can inhibit mineral absorption.

Functions of Minerals

Minerals play several critical roles in the body:

• Contribute to body structures (e.g., bones, teeth).

• Regulate body processes such as blood pressure (BP), water balance (H2O), and energy metabolism.

• Affect growth and development.

• Act as cofactors for enzymes.

Minerals in the Diet

Different food groups provide various minerals:

Vegetables and Fruit	Whole Grains	Protein Foods
Iron, Calcium, Potassium, Magnesium, Molybdenum	Iron, Zinc, Selenium, Copper, Magnesium, Chromium, Sulfur, Manganese, Sodium, Potassium, Phosphorus	Iron, Zinc, Calcium, Magnesium, Potassium, Chromium, Sulfur, Iodine, Selenium, Phosphorus, Copper, Manganese, Fluoride, Molybdenum

Bone Health

Bone Structure and Composition

Bones are composed of a protein matrix that is hardened by minerals, primarily calcium and phosphorus, but also magnesium, fluoride, and others. Adequate nutrition and exercise are essential for bone health.

• Protein and vitamin C are necessary for the protein matrix.

• Calcium and other minerals provide hardness.

• Vitamin D is required for mineral absorption.

• Strength exercise stimulates bone formation.

Types of Bone

• Trabecular bone (spongy bone): Found at the ends of long bones and inside vertebrae; more metabolically active and sensitive to changes in mineral status.

• Cortical bone (compact bone): Dense and forms the outer layer of bones; provides strength and structure.

Bone Mass

Bone mass is influenced by age and sex. Peak bone mass is typically achieved in early adulthood, after which bone loss gradually occurs. Women experience accelerated bone loss after menopause.

• Men generally achieve higher peak bone mass than women.

• Bone loss is a normal part of aging.

Osteoporosis

Osteoporosis is a disorder characterized by reduced bone mass, increased bone fragility, and a higher risk of fractures. It is often a silent threat, with symptoms appearing only after significant bone loss has occurred.

• Major public health problem, especially in older adults.

• Risk factors include age, sex (higher in females), race, family history, body size, lifestyle (smoking, alcohol use), and diet.

Risk Factor	How it Affects Risk
Gender	Women have higher risk due to lower bone mass and hormonal changes after menopause.
Age	Bone loss increases with age.
Family history	Having a family member with osteoporosis increases risk.
Body size	Individuals who are small or thin have increased risk due to less bone mass.
Smoking	Weakens bones.
Exercise	Weight-bearing exercise strengthens bone and increases bone mass.
Alcohol abuse	Long-term abuse reduces bone formation and interferes with calcium absorption.
Diet	Low calcium and vitamin D intake increases risk; high sodium and protein intake can accelerate bone loss.

Osteoporosis Prevention

• Achieve the highest peak bone mass possible through weight-bearing exercise and adequate intake of vitamin D, vitamin C, calcium, zinc, magnesium, and potassium.

• Avoid smoking and excessive alcohol consumption.

• Monitor sodium and protein intake.

Major Minerals in Bone Health

Calcium

Calcium is the most abundant mineral in the body, accounting for 1–2% of adult body weight. About 99% is stored in bones and teeth, with the remaining 1% in body fluids and cells.

• Absorbed by active transport and passive diffusion, depending on vitamin D availability.

• Bioavailability is decreased by tannins, fiber, phytates, and oxalates.

• Functions include muscle contraction, neurotransmitter release, blood pressure regulation, cell communication, and blood clotting.

• Levels are regulated by hormones: calcitonin (lowers blood calcium) and parathyroid hormone (PTH, raises blood calcium).

Blood Calcium Regulation:

• High blood calcium: Calcitonin from the thyroid gland inhibits calcium release from bones and increases excretion by kidneys.

• Low blood calcium: PTH from the parathyroid glands stimulates calcium release from bones, increases reabsorption by kidneys, and activates vitamin D to increase intestinal absorption.

Calcium Requirements and Sources:

• RDA (19–50 years): 1000 mg/day

• UL: 2500 mg/day

• Sources: Dairy products, dark green vegetables, fish with bones, fortified foods

Deficiency: Osteoporosis

Excess: Constipation, loss of appetite, abnormal heartbeat, weight loss, fatigue, frequent urination, soft tissue calcification, kidney stones, heart attack

Phosphorus

Phosphorus makes up about 1% of an adult's body, with 85% found in bones and teeth. It is more readily absorbed than calcium and plays both structural and regulatory roles.

• In soft tissues, phosphorus is needed for phospholipid, DNA, RNA, and ATP structures, enzyme regulation, and maintaining cellular acidity.

• RDA (adults): 700 mg/day

• UL: 4000 mg/day

• Sources: Dairy, meat, cereal, bran, eggs, nuts, fish, food additives

• Deficiency: Rare, but can cause bone loss, weakness, loss of appetite

• Excess: Rare, but can lead to bone resorption

Vitamin D: Regulation of Blood Calcium and Phosphorus

Vitamin D is essential for maintaining normal blood levels of calcium and phosphorus. When blood calcium is low, vitamin D:

1. Increases calcium extraction from bones

2. Increases calcium retention by the kidneys

3. Increases calcium absorption by the intestine

Magnesium

About 50–60% of magnesium is found in bone, with the rest inside cells as the second most abundant intracellular ion after potassium. Magnesium is essential for structural maintenance and as a cofactor for over 300 enzymes.

• ~50% absorbed; absorption enhanced by vitamin D, inhibited by phytates and calcium supplements

• Functions: Regulates cardiovascular system, energy generation, calcium regulation, blood pressure regulation, ATP stabilization, nerve and muscle function, DNA/RNA/protein synthesis

• Kidneys regulate magnesium excretion

• Deficiency: Common in alcoholism, malnutrition, kidney/GI disease, diuretic use; symptoms include osteoporosis, nausea, muscle weakness, cramping, irritability, mental derangement, blood pressure and heartbeat changes

• Excess: Rare from food; supplements may cause sleepiness (glycinate) or diarrhea (citrate)

• RDA: Males 420 mg/day, females 320 mg/day

• Sources: Leafy greens, nuts, seeds, legumes, bananas, whole grain germ and bran

Additional info: Magnesium is used up during stress and acts as a muscle relaxant and pain reducer, aiding sleep and stress management.

Sulfur

Sulfur is found in protein foods and is a component of sulfur-containing amino acids (e.g., methionine, cysteine) necessary for protein synthesis. It is also present in B vitamins (thiamin, biotin) and in nonfood additives (e.g., sulfur dioxide, sodium sulfite).

• Part of all cells and extracellular compartments

• Component of keratin (nails, hair, skin)

• Involved in DNA repair

• No recommended daily intake; deficiency only occurs if protein is absent from the diet