Major Minerals: Calcium and Phosphorus – Functions, Regulation, and Dietary Sources

Major Minerals: Calcium and Phosphorus

Calcium (Ca)

Calcium is an essential mineral for human health, playing a critical role in bone structure, muscle function, and cellular processes. It is the most abundant mineral in the body.

• Main Bodily Functions:

  • Forms hydroxyapatite with phosphate, providing hardness to bones and teeth.

  • Required for muscle contraction, nerve transmission, and blood clotting.

  • Maintains vascular tone and cell signaling.

• Recommended Dietary Allowance (RDA):

  • Adults: 1,000 mg/day

  • Adults 51+: 1,200 mg/day

• Upper Limit (UL):

  • Adults 19-50: 2,500 mg/day

  • Adults 51+: 2,000 mg/day

Food Sources

• Dairy products (milk, cheese, yogurt)

• Sardines, leafy greens (e.g., broccoli, kale)

• Fortified foods (e.g., orange juice, cereals)

Things That Limit Absorption

• Oxalates & phytates (found in some plant foods)

• Lack of vitamin D

Deficiency

• Osteopenia, osteoporosis (bone loss)

• Muscle spasms, convulsions

• Impaired nerve function

Excess/Toxicity

• Kidney stones

• Calcification of soft tissues

• Gastrointestinal upset

• Can interfere with other mineral absorption

Main dietary concern: Over 60% of females & 65% of females deficient in calcium. Additional info: These statistics highlight the importance of adequate calcium intake, especially in populations at risk for osteoporosis.

Calcium Homeostasis in the Body

Calcium levels in the blood are tightly regulated by hormonal control involving the thyroid and parathyroid glands.

• High Blood Calcium:

  • Thyroid gland releases calcitonin.

  • Calcitonin lowers blood calcium by:

    • Inhibiting calcium release from bones

    • Increasing calcium excretion by kidneys

    • Decreasing intestinal absorption

• Low Blood Calcium:

  • Parathyroid glands release parathyroid hormone (PTH).

  • PTH raises blood calcium by:

    • Stimulating calcium release from bones

    • Reducing calcium excretion by kidneys

    • Increasing intestinal absorption (via activation of vitamin D)

Blood Calcium	Gland + Releases	Bone Response	Kidney Response	Intestine Response
High	Thyroid (Calcitonin)	↓ Ca release	↑ Ca excretion	↓ Ca absorption
Low	Parathyroid (PTH)	↑ Ca release	↓ Ca excretion	↑ Ca absorption

Clinical Terms

• Hypocalcemia: Abnormally low blood calcium levels; can cause muscle spasms and cardiac arrhythmias.

• Hypercalcemia: Abnormally high blood calcium levels; can cause kidney stones and impaired absorption of other minerals.

Example

• If a person has low calcium for many years, the parathyroid gland will release PTH, increasing bone resorption and raising blood calcium, but potentially weakening bones.

Phosphorus (P)

Phosphorus is the second most abundant mineral in the body, essential for bone and teeth formation, energy metabolism, and cellular function.

• Main Bodily Functions:

  • Forms hydroxyapatite with calcium in bones and teeth

  • Part of energy storage molecules (ATP)

  • Component of DNA and RNA (phosphate backbone)

• Recommended Dietary Allowance (RDA): 700 mg/day

• Upper Limit (UL): 4,000 mg/day

Food Sources

• Animal products (meat, eggs, dairy)

• Legumes, nuts, seeds

• Cola beverages (contain phosphoric acid)

Deficiency

• Rare; usually only in cases of malnutrition or certain medical conditions

• Symptoms: Muscle weakness, bone pain

Excess/Toxicity

• Hyperphosphatemia (usually associated with kidney disease)

• Calcification of soft tissues

Main dietary concern: None for general population, but excess intake can be problematic for those with kidney disease.

Key Interactions

• Phosphorus combines with calcium to form hydroxyapatite, the hard component of bones and teeth.

• High phosphorus intake can interfere with calcium absorption.

Example

• Animal products are especially high in phosphorus compared to vegetables and fruits.

• Sodium is a mineral that can combine with phosphate in the body, but calcium is the primary mineral forming hydroxyapatite.

Additional Info

• Spinach is not a great source of absorbable calcium due to its high oxalate content, which binds calcium and limits its absorption.

• Calcium and phosphorus metabolism are closely linked; imbalances can affect bone health and overall metabolism.