Major Minerals: Calcium, Phosphorus, Magnesium, and Sulfur

This session discusses four major minerals: calcium, phosphorus, magnesium, and sulfur, focusing on their physiological roles, recommended intake guidelines, food sources, and medical nutrition therapy considerations throughout the life cycle. It also describes how bone mineral density changes over the lifespan.

Calcium

Physiological Roles
- Most abundant mineral in the body.
- Serum Calcium: 1\% of bodily calcium is in body fluids, referred to as serum calcium. It mediates:
  - Blood vessel contraction and dilation.
  - Muscle function.
  - Blood clotting.
  - Nerve transmission.
  - Hormonal secretion.
- Bone and Teeth Calcium: 99\% of total body calcium is stored in the bones and teeth.
  - Contributes to the structure of the skeletal system in the form of hydroxyapatite crystals.
- Physiological Priority: Maintaining serum calcium levels is the first physiological priority over maintaining bone calcium density, as serum calcium is crucial for vital processes (muscle function, blood clotting, nerve signal transmission). Failure of these processes can be fatal.
- Calcium in bones readily enters the bloodstream if serum calcium levels drop.
Bone Mineral Density (BMD) Changes Throughout Life
- Low bone mineral density (BMD) is not immediately dangerous, but can lead to negative health outcomes later in life.
- Calcium Absorption Efficiency: Changes throughout the life cycle.
  - Newborns: absorb 55\% to 60\% of ingested calcium.
  - Children and Teens: absorb up to 50\%.
  - Adults: absorb about 25\%.
  - Pregnancy: absorption efficiency doubles.
- Vitamin D's Role: Facilitates calcium absorption; vitamin D deficiency increases calcium deficiency risk.
- Bone Growth Periods: Calcium absorption efficiency mirrors periods of active bone growth.
  - Early life (before about age 25): Rapid period of bone growth.
  - Peak bone mass occurs between ages 20 and 30 years.
  - After about age 30: Bone mass gradually decreases.
  - Post-menopause: Decline is more rapid for women.
- Factors Influencing BMD: Dietary adequacy of nutrients (calcium, phosphorus, vitamin D, vitamin K, magnesium), amount of weight-bearing exercise, sleep adequacy, and various other factors.
- BMD Diagrammatic Representation:
  - X-axis: Age by decade.
  - Y-axis: Bone mineral density.
  - Gender Differences: Men tend to have higher BMD than women due to hormonal factors and greater overall body mass.
  - Lifespan Trajectory: Rapid bone mineralization early in life, peaking between ages 20 and 30. Gradual decrease after age 30. Faster decline for women post-menopause.
  - Impact of Early Poor Mineralization: Inadequate calcium intake early in life can lead to very poor BMD later in life.
Recommended Dietary Allowance (RDA)
- An RDA exists for calcium and varies throughout the life cycle due to absorption efficiency differences and variations in bone mineral density building capacity.
Food Sources
- Dairy Products: Excellent sources including milk, cheese, yogurt, and kefir.
- Non-Dairy/Plant Sources: For individuals with lactose intolerance: dark green leafy vegetables (e.g., spinach) and soybeans/soybean products (e.g., tofu).
Deficiency Considerations
- Chronic Poor Intake: Long-term poor calcium intake can lead to poor BMD later in life, resulting in osteoporosis and increased risk of fractures.
- High-Risk Groups:
  - Postmenopausal Women: Especially high risk because decreases in estrogen lead to decreased calcium absorption, increased calcium excretion in urine, and increased release of calcium from bones into the serum. During this stage, BMD can be maintained but no longer built.
  - Lactose Intolerant Individuals: Increased risk of developing calcium deficiency. Supplementation is sometimes required.
Toxicity Considerations (Hypercalcemia and Hypercaluria)
- Health Risks (According to NIH): Poor muscle tone, renal insufficiency, hypophosphatemia, constipation, nausea, weight loss, fatigue, polyuria, heart arrhythmias, and a higher risk of cardiovascular disease (CVD) mortality.
- Definitions:
  - Hypercalcemia: High levels of calcium in the blood.
  - Hypercaluria: High levels of calcium in the urine.
  - Polyuria: Excessive urination.
  - Hypophosphatemia: Low levels of phosphorus in the blood.
  - CVD: Cardiovascular disease.
- Upper Limit (UL): A UL has been established for calcium due to associated health risks.

Phosphorus

Physiological Roles
- Skeletal Structure: 85\% of bodily phosphorus makes up hydroxyapatite crystals with calcium in the bones and teeth, serving as primary structural materials for the skeletal system.
- Growth and Metabolism: Necessary for adequate growth as it is part of DNA and RNA.
- Energy Metabolism: Involved in energy metabolism, notably as part of ATP (adenosine triphosphate), which contains three phosphorus-containing groups.
- Enzyme & B Vitamin Activation: Adding a phosphate group is necessary for the activation of several enzymes and B vitamins.
- Cellular Structure: Key component of phospholipids, which provide structure to cell membranes and other key lipoproteins.
Recommended Dietary Allowance (RDA)
- An RDA exists for phosphorus and varies throughout the lifespan, similar to the RDA for calcium.
Food Sources
- Similar to calcium, dairy products are an excellent source.
- Additional sources include lentils, nuts, seeds, and potatoes.
Deficiency Considerations
- Rarity: Deficiency in the US due to inadequate intake is extremely rare.
- Symptoms: Can lead to muscle weakness, bone pain, and poor bone mineral density.
Toxicity Considerations
- Rarity: Toxicity is also rare.
- Processed Foods: Phosphorus has become increasingly present in processed foods (e.g., phosphoric acid in dark soda).
- Negative Implications: Excessive phosphorus intake appears to have negative physiological implications; the extent and type are areas of ongoing research.
- Upper Limit (UL): Based on current research, a UL has been established for most stages of the life cycle.

Magnesium

Physiological Roles
- Bone Health: Roughly 50\% of bodily magnesium is in the bones, where it helps maintain bone integrity by contributing to bone mineralization.
- Electrolyte Function: 1\% of bodily magnesium is in the extracellular fluid, acting as an electrolyte. It maintains the electrochemical gradient between the extracellular and intracellular space, similar to sodium and potassium.
- Enzyme Cofactor: The remaining 40\% to 50\% of bodily magnesium is in the muscles and soft tissues. It acts as a cofactor in hundreds of enzyme systems crucial for energy metabolism, similar to many water-soluble vitamins.
- Muscle Contraction & Blood Clotting: Aids in muscle contraction and blood clotting.
- Nutrient Transport: Facilitates the transport of calcium and phosphorus across cell membranes.
- Immune Health: Promotes immune health by facilitating the production of an endogenous antioxidant.
Recommended Dietary Allowance (RDA)
- An RDA exists for magnesium and varies throughout the lifespan.
- The RDA for adults is 300 to 400 mg per day.
Food Sources
- Found in a wide variety of nuts and seeds, such as pumpkin seeds, almonds, and chia seeds.
Deficiency Considerations
- Rarity: Deficiency in the US due to inadequate intake is rare.
- Treatment Challenge: Magnesium deficiency can be challenging to treat with oral supplementation because diarrhea (a common side effect of magnesium supplements) is also a risk factor for magnesium deficiency, potentially worsening the condition.
Toxicity Considerations
- Rarity from Food: Toxicity due to excessive food intake is rare.
- Supplementation Risks: Supplementation is increasingly common and can lead to negative health outcomes, notably diarrhea.
- Upper Limit (UL): A UL has been established for magnesium, but it applies to supplemental magnesium only, not magnesium from food sources.

Sulfur

Physiological Roles
- Protein Structure: Necessary for certain protein structures to maintain their shape.
- Rigid Proteins: Some of the most rigid proteins in the body (e.g., those making up the skin, hair, and nails) have high sulfur content.
- Amino Acid Component: Two amino acids necessary for human protein synthesis contain sulfur: methionine and cysteine.
- Insulin Example: Insulin, a protein, contains a high amount of the amino acid cysteine. The sulfur bridges formed between cysteine amino acids are largely responsible for insulin's shape and function.
Food Sources
- Found in high-protein foods because the amino acids methionine and cysteine contain sulfur.
Deficiency Considerations
- Rarity: Sulfur deficiency is only seen in cases of severe protein deficiency, as a diet with adequate protein typically provides adequate sulfur.
Recommended Intake
- No specific recommended intake levels exist for sulfur, although it is an essential nutrient.

Conclusion

Calcium, phosphorus, magnesium, and sulfur are all major minerals essential for various bodily functions.

Calcium and Phosphorus: Primarily form the hydroxyapatite crystals of the skeletal system. Adequate intake is especially crucial early in life when bone mineral density can be gained.
Magnesium: Plays a diverse range of physiological roles, acting as a cofactor, an electrolyte, and contributing to bone health.
Sulfur: Crucial for protein structure and found in sulfur-containing amino acids. Its status is rarely addressed independently of protein status, but it is an essential nutrient.