Chapter 11: Major Minerals and Bone Health

Introduction to Minerals

• Definition of Minerals: Minerals are essential inorganic elements required by the body in small amounts to maintain health and support physiological functions.

• Classification of Minerals:

  • Major Minerals: These are required in the diet in amounts greater than $100\,mg/day$. In the physical body, they represent more than $0.01\%$ of total body weight.

  • Trace Minerals: These are required in the diet in amounts less than $100\,mg/day$. They represent less than $0.01\%$ of total body weight.

• Minerals in the Diet by Food Group:

  • Grain Products (fortified or enriched usually): Provide Iron, Zinc, Selenium, Magnesium, Potassium, Phosphorus, Chromium, Molybdenum, and Copper.

  • Vegetables and Fruit: Provide Iron, Calcium, Potassium, Magnesium, Chromium, Molybdenum, Sulfur, Iodine, Manganese, Copper, and Phosphorus.

  • Milk and Alternatives: Provide Calcium, Zinc, Phosphorus, Potassium, Magnesium, iodine, and Fluoride.

  • Meat and Alternatives: Provide Iron, Zinc, Selenium, Magnesium, Potassium, Chromium, Sulfur, Copper, Phosphorus, Sodium, and Manganese.

General Mineral Principles and Bioavailability

• Dietary Balance: To maintain optimal health, minerals must be consumed in correct proportions relative to one another.

• Bioavailability: This refers to the degree to which a mineral is absorbed and used by the body. Bioavailability is a critical factor in mineral nutrition.

  • Phytates: Found in plant foods, phytates can bind to minerals like calcium, zinc, and iron, limiting their absorption.

• Toxicity and Upper Limits (ULs): Because minerals can become toxic if consumed in excess, Tolerable Upper Intake Levels (ULs) have been established for many.

• Minerals as Enzyme Cofactors:

  • Many minerals function as cofactors for enzymes.

  • An incomplete enzyme is inactive until a mineral cofactor binds to it, creating an active enzyme.

  • The active enzyme then allows specific compounds (e.g., Compound A) to be converted into products (e.g., Product A).

Nutrients and Essential Components for Bone Health

• Bone health is dependent on a complex interaction of the following nutrients:

  • Calcium

  • Phosphorus

  • Magnesium

  • Protein

  • Vitamin A

  • Vitamin D

  • Vitamin C

  • Fluoride

  • Zinc

Calcium Overview and Distribution

• Abundance: Calcium is the most abundant mineral found in the human body.

• Distribution:

  • $99\%$ of Calcium: Located in the solid mineral deposits of the bones and teeth. It provides structural integrity. Phosphorus in blood (low= vit. d absorption, high = p lost in urine)

  • $1\%$ of Calcium: Found in intracellular fluid, blood, and extracellular fluid. This small fraction is vital for regulatory roles.

• Regulatory Functions of Calcium:

  • Nerve transmission.

  • Muscle contractions. (actin and myosin to interact and cause muscle contractions)

  • Blood pressure regulation.

  • Release of hormones.

  • Blood clotting.

  • Regulation of the heart beat.

• Chemical Structure: Calcium in the bones is a critical component of hydroxyapatite crystals.

Calcium Absorption and Bioavailability

• Mechanisms of Absorption: Calcium is absorbed in the small intestine via two primary methods:

  • Active Transport: This process is dependent on Vitamin D. It involves three steps:

    1. Vitamin D turns on the synthesis of calcium transport proteins.

    2. Calcium transport proteins shuttle calcium across the mucosal cell.

    3. A calcium pump requiring energy ($ATP$) moves calcium from the mucosal cells into the bloodstream.

  • Vit D deficiency recuses Ca intake by 10-25%, pregnancy = higher calcium absorption b/c of estrogen, menopause = lower Ca absorption

  • Passive Diffusion: Occurs when calcium concentrations in the intestinal lumen are high.

• Factors Increasing Absorption:

  • Consuming small, frequent intakes of calcium throughout the day.

  • Pregnancy (the body adapts to absorb more).

• Factors Decreasing Absorption: (spread out calcium throughout your day)

  • Oxalates: Found in spinach and chocolate.

  • Phytates: Found in whole grains, legumes, nuts, seeds, and some vegetables.

  • Tannins: Found in tea.

  • Fiber: High fiber intake can interfere with absorption.

  • Mineral Competition: High levels of Zinc ($Zn$), Iron ($Fe$), and Magnesium ($Mg$) can compete for absorption.

  • Medical/Physiological Factors: Medications, low stomach acid, and fat malabsorption reduction.

  • Dietary Context: Low calcium intake can amplify the negative impact of these inhibitory dietary components.

Regulation of Blood Calcium Levels

• Low Blood Calcium Response:

  • The Parathyroid glands sense low calcium and release Parathyroid Hormone ($PTH$).

  • $PTH$ stimulates the release of calcium from the bone (bone resorption).

  • $PTH$ signals the kidneys to reabsorb calcium rather than excreting it.

  • $PTH$ activates Vitamin D, which increases calcium absorption in the intestines.

• High Blood Calcium Response:

  • The Thyroid gland releases the hormone Calcitonin.

  • Calcitonin inhibits the release of calcium from the bone, helping to lower blood levels back to normal.

Dietary Sources and Requirements of Calcium

• Recommended Intake: The general requirement is approximately $1000\,mg/day$.

• Food Source Values (Approximate):

  • Yogurt ($3/4$ cup): $330\,mg$

  • Milk (Cow's or alternative, $1$ cup): $300\,mg$

  • Kefir ($1$ cup): $270\,mg$

  • Brick Cheese ($3\,cm$ cube): $250\,mg$

  • Salmon with bones ($1/2$ can): $240\,mg$

  • Sardines with bones ($1/2$ can): $200\,mg$

  • Whey Protein Powder ($1$ scoop): $200\,mg$

  • Blackstrap Molasses ($1$ tbsp): $180\,mg$

  • Cottage Cheese ($1$ cup): $150\,mg$

  • Collard Greens ($1/2$ cup cooked): $115\,mg$

  • Tempeh ($4\,oz$): $110\,mg$

  • Kale ($1$ cup): $105\,mg$

  • White Beans ($1/2$ cup cooked): $95\,mg$

  • Sesame Seeds ($1$ tbsp): $95\,mg$

  • Almonds ($1/4$ cup): $95\,mg$

• Soft Drink Trends: In the Canadian diet, soft drinks are increasingly replacing milk. They contain no calcium, are high in sugar, and negatively affect the calcium intake of teenagers. Canadian males ($14\text{--}18\,yrs$) consume an average of $376\,ml/day$ of soft drinks, while females consume $179\,ml/day$.

Calcium Supplementation and Toxicity

• Supplementation Guidelines:

  • Multivitamins usually do not contain enough calcium to meet full needs.

  • Choose supplements containing calcium alone or calcium with Vitamin D.

  • Taking lower doses more often is more efficient for absorption.

• Forms of Supplements:

  • Calcium Carbonate: Should be taken with a meal (requires stomach acid for absorption).

  • Calcium Citrate: Can be taken at any time.

• Interactions: Antacids containing aluminum and magnesium may increase the loss of calcium.

• Toxicity ($UL$):

  • Consuming up to $2.5\,g/day$ is generally not a concern.

  • More than $2.5\,g/day$ can lead to lower intestinal absorption and interfere with the absorption of other minerals, specifically iron and zinc. (nausea, vomiting etc)

Bone Anatomy and Bone Mass Lifecycle

• Bone Tissue Types:

  • Cortical (Compact) Bone (80%): Dense outer layer that provides strength.

  • Trabecular Bone: Internal lattice-like structure that provides flexibility. (wrist, pelvis)

• Hydroxyapatite: The crystalline structure formed by Calcium and Phosphorus in bone.

• Bone Remodeling Process: Bone is living tissue that is constantly remodeled.

  • Osteoclasts: Cells responsible for bone resorption (breaking down bone).

  • Osteoblasts: Cells responsible for bone formation (building bone).

• Bone Mass Over the Lifespan:

  • Childhood and Adolescence: A critical period for bone growth. Bone mass increases rapidly during puberty.

  • Peak Bone Mass: Reached at approximately age $30$. Men generally achieve a higher peak bone mass than women.

  • Bone Loss: Slow bone loss begins for both genders after age $35$.

  • Menopause: Women experience accelerated bone loss for about $5$ years after menopause due to decreased estrogen levels.

Osteoporosis: Prevalence and Risk Factors

• Definition: Known as "porous bone," it is a silent disease that weakens bones, leading to fractures, most commonly in the wrist, spine, and hip.

• Statistics in Canada:

  • $2\,million$ Canadians over age $50$ have osteoporosis.

  • Affects $1/4$ of women and $1/8$ of men over age $50$.

  • Responsible for $80\%$ of fractures in individuals over $60\,years$.

  • $20\%$ of hip fractures result in death; $50\%$ result in permanent disability.

  • Treatment costs exceed $1.9\,billion$ per year in Canada.

  • More women die from osteoporotic fractures than from breast and ovarian cancer combined.

• Risk Factors:

  • Gender: Twice as common in women (lower peak mass and post-menopausal loss).

  • Age: Risk increases as bone loss is a normal part of aging.

  • Race: Caucasians and Southeast Asians have lower bone density compared to Blacks.

  • Family History: Genetic predisposition increases risk.

  • Body Size: Thin and light individuals have less bone mass to lose.

  • Smoking: Weakens bones.

  • Exercise: Lack of weight-bearing exercise increases risk.

  • Alcohol Abuse: Reduces bone formation and interferes with calcium absorption.

  • Diet: Lack of Calcium and Vitamin D during bone formation years results in lower peak mass.

• Prevention: Weight-bearing exercise (carrying your own weight, like walking or jogging) increases bone density early in life and decreases loss later in life.

Phosphorus

• Location: $85\%$ is in bones; $15\%$ in soft tissues and fluids.

• When P levels low = activates Vit d. to enhance Ca and P absorption

• Biological Functions:

  • Component of hydroxyapatite in bones.

  • Part of cell membranes (phospholipids).

  • Synthesis of genes ($DNA/RNA$) and protein.

  • Energy storage and release ($ATP$, creatinine).

  • Involved in metabolic reactions.

  • Maintains acid-base balance.

• Absorption and Toxicity:

  • Absorbed more readily than calcium, with or without Vitamin D.

  • Toxicity: Rare, but can lead to bone resorption.

  • Deficiency: Rare; usually linked to medical conditions (premature infants, alcoholics, vegans) and can cause bone loss, weakness, and loss of appetite.

• Dietary Sources ($RDA \approx 700\,mg$): Found in sunflower seeds, milk, yogurt, meat, and grains.

Magnesium and Sulfur

• Magnesium Overview: regulates Ca homeostasis and supports vit d, hormone function (PTH)

  • $50\text{--}60\%$ is found in bone for structural maintenance.

  • Functions: Cofactor for over $300$ enzymes. Necessary for $ATP$ generation from macronutrients. Essential for the Sodium-Potassium ($Na\text{--}K$) pump, nerve/muscle function, and synthesis of $DNA$, $RNA$, and protein.

  • Deficiency: Rare; can occur with alcoholism, kidney disease, or diuretic use. Symptoms include nausea, cramping, mental derangement, and heart rhythm changes.

  • Toxicity: Rare; $UL$ is $350\,mg$ from nonfood sources (e.g., supplements).

• Sulfur:

  • Sources: Found in protein foods, sulfur-containing amino acids (methionine, cysteine), and vitamins (thiamin, biotin).

  • Functions: Essential for protein synthesis. Cysteine is a part of glutathione peroxidase (antioxidant). Involved in acid-base regulation.

  • Additives: Found in sulfur dioxide, sodium sulfite, and sodium bisulfite.

  • Requirements: There is no specific recommended daily intake for sulfur.