Hydroxyapatite comes in two forms: a fluoride-free toothpaste that rebuilds tooth surfaces and calms sensitivity, and a swallowed bone-derived calcium supplement for the aging skeleton. Easing sensitive teeth is the clearest benefit; cavity prevention roughly matches fluoride but the evidence is thin and industry-funded. Bone benefit is real but small. Most safety concerns involve the swallowed form. (Full Review)
| Marker | Target | Why |
|---|---|---|
| Serum calcium | 9.4–9.8 mg/dL | Detects calcium overload from the ingested form |
| 25-hydroxyvitamin D | 40–60 ng/mL | Governs how much calcium is absorbed |
| Intact parathyroid hormone (PTH) | 15–40 pg/mL | Flags parathyroid-driven calcium problems |
| Serum phosphate | 3.0–4.0 mg/dL | Tracks the other half of the bone mineral |
| 24-hour urinary calcium | 100–250 mg/24h | Gauges kidney-stone risk on the ingested form |
| Estimated glomerular filtration rate (eGFR) | >90 mL/min | Confirms kidneys can handle a calcium load |
| Bone density (DEXA T-score) | Better than −1.0 | Tracks the skeletal response over time |
Cadence: Recheck blood calcium and vitamin D at ~3 months, then every 6–12 months; bone density scan every 1–2 years; kidney function and urinary calcium periodically for those at stone or kidney risk