What Is Calcium and What Does It Do in the Body?

Calcium is the most abundant mineral in the body, with approximately 99% stored in bones and teeth. The remaining 1% circulates in blood and soft tissues. The body uses calcium to:

  • Form strong bones and teeth
  • Help muscles contract and relax for normal movement
  • Transmit nerve impulses
  • Make blood clot normally
  • Regulate cell secretions, cell division, and cell multiplication
  • Assist with enzyme reactions

How Much Calcium Is Needed?

A balanced diet provides approximately 1,000 milligrams of calcium daily. Requirements increase during growth and aging. Adolescents aged 9–18 need 1,300 mg daily to support bone development, while adults 50 and older require at least 1,200 mg daily to preserve bone density.

Insufficient calcium intake forces the body to "borrow" calcium from bones. Over time, this leads to osteoporosis — a condition where bones become weak and fracture easily.

Calcium Needs for CKD Patients

Calcium requirements for those with chronic kidney disease differ significantly from the general population. As kidney function declines, patients may retain excess calcium, potentially developing hypercalcemia (high calcium levels).

Calcium and phosphorus work together to maintain balance. Advanced kidney disease can cause elevated phosphorus, leading to hypocalcemia (low calcium). A complex relationship exists between the parathyroid gland, vitamin D, and kidneys that becomes disrupted in advanced CKD (typically stage IIIb and beyond). Doctors assess calcium status by measuring calcium, phosphorus, vitamin D, and parathyroid hormone levels.

Know Your Calcium and Phosphorus Levels

Working with a renal dietitian and physician helps maintain balanced calcium and phosphorus levels. According to National Kidney Foundation guidelines, CKD stages 3–4 patients should maintain phosphorus between 2.7–4.6 mg/dL, while dialysis patients should target 3.0–5.5 mg/dL. The target calcium range is 8.4–10.2 mg/dL. Levels exceeding 10.2 may require dietary adjustments or medication modifications.

High-Calcium Foods to Know

Most high-calcium foods are also high in phosphorus and may not be recommended for CKD patients:

  • Blackstrap molasses
  • Calcium-fortified or enriched foods
  • Canned or powdered milk
  • Cheese and cottage cheese
  • Ice cream
  • Milk and milk-based beverages
  • Pizza
  • Canned sardines or salmon with bones
  • Spinach
  • Yogurt (including frozen)

Portion sizes significantly affect calcium intake. Consult your dietitian or physician for personalized dietary recommendations.

Treating and Managing Calcium Levels

  • Regular testing of calcium, phosphorus, and PTH levels
  • Reducing dietary phosphorus intake
  • Taking phosphorus binders as prescribed
  • Taking active vitamin D if prescribed
  • Taking calcium supplements if prescribed
  • Taking calcimimetic medication if prescribed
  • Parathyroid gland surgery if necessary