Calcium is the body's main bone-building mineral. Correcting a genuine shortfall is worthwhile and, with vitamin D and weight-bearing exercise, modestly slows bone loss. For people already getting enough, supplement benefit looks small while downsides—digestive upset, kidney stones, and an unsettled heart-risk question—remain; food behaves more favorably than supplements. (Full Review)

Protocol

Intake Target

1,000–1,200 mg/day

Total calcium, food first; supplement only to close the gap

Per-Dose Limit

≤500 mg elemental

Split larger daily totals across the day; take with meals

Form Selection

Carbonate or Citrate

Carbonate with food; citrate if low stomach acid or constipation

Time to effect

Bone Density

Months to years

Measurable bone-density effects build slowly

Fracture Risk

Years

Fracture-risk effects, where present, emerge over years of consistent intake

Benefits

High: Correction and prevention of deficiency

Medium: Reduced bone loss; modest fracture risk reduction

Low: Blood pressure reduction; reduced risk of colorectal adenomas

Speculative: Support for healthy body weight and metabolic markers

Contraindications

Hypercalcemia

Primary hyperparathyroidism

Sarcoidosis or other granulomatous disease

Severe chronic kidney disease (CKD stage 4–5, eGFR below 30 mL/min/1.73m²)

History of calcium-containing kidney stones

Key Interactions

Thiazide diuretics (hydrochlorothiazide, chlorthalidone)

Thyroid hormone (levothyroxine) and bisphosphonates (alendronate, risedronate)

Tetracyclines (doxycycline) and fluoroquinolones (ciprofloxacin, levofloxacin)

Iron and zinc supplements

Vitamin D supplements

Magnesium supplements

Calcium-containing antacids

Risk & Side Effects

High: Gastrointestinal side effects

Medium: Increased risk of kidney stones; cardiovascular events

Low: Hypercalcemia and milk-alkali syndrome; interference with mineral and drug absorption

Speculative: Possible association with prostate cancer

Monitoring

Marker	Target	Why
Serum calcium	9.0–10.0 mg/dL	Detects hypercalcemia from over-supplementation
25-hydroxyvitamin D	40–60 ng/mL	Vitamin D drives calcium absorption; guides whether calcium will be used
Intact parathyroid hormone (PTH)	15–40 pg/mL	High PTH signals inadequate calcium/vitamin D; low PTH may signal excess
24-hour urinary calcium	100–250 mg/24h	Identifies high excretors at risk of kidney stones
Serum phosphorus	2.5–4.0 mg/dL	Balances with calcium in bone metabolism
Estimated GFR (eGFR)	>60 mL/min/1.73m²	Reduced kidney function raises risk from calcium load

Cadence: Baseline, then ~3–6 months after starting and every 6–12 months for higher-risk users

Qualitative Assessment

Bowel regularity and absence of constipation or bloating
Absence of kidney stone symptoms (flank pain, blood in urine)
General energy and muscle function (no cramping or weakness)
Adherence to dietary calcium goals and overall bone-supportive routine (exercise, vitamin D)

Calcium for Health & Longevity

Protocol

Benefits

Risk & Side Effects

Monitoring

Qualitative Assessment