Calcium Hydroxyapatite

Calcium hydroxyapatite is the calcium phosphate that makes up the mineral phase of bone and tooth enamel. It is written either as the formula unit Ca5(PO4)3OH, molecular weight 502.31, or as the crystallographic unit cell Ca10(PO4)6(OH)2; CAS 1306-06-5, IUPAC name pentacalcium hydroxide triphosphate. Stoichiometric material is 39.9% calcium and 18.5% phosphorus, a calcium-to-phosphorus molar ratio of 1.67, and that ratio is the fingerprint buyers should ask to see on the certificate, because commercial calcium phosphates drift. It is a white, odourless, tasteless powder, stable in air, practically insoluble in water and readily soluble in dilute hydrochloric or nitric acid. Functionally it is a concentrated source of two nutrients at once, calcium and phosphorus, and it doubles as an anticaking and free-flow agent and a direct-compression tablet filler. Two genuinely different articles are sold under this name and they must not be quoted against each other. The synthetic grade is precipitated from calcium and phosphate salts, contains no animal material, and is vegan, vegetarian and straightforward for halal and kosher certification. Microcrystalline hydroxyapatite — MCHA, also sold as MCHC or ossein hydroxyapatite — is a whole-bone concentrate from bovine bone, and it is not a pure compound: published compositions describe roughly 26% collagen plus around 9% non-collagenous protein alongside the mineral, and it carries the magnesium, phosphorus, zinc and bone proteins that come with the matrix. That extra organic fraction is exactly why some formulators want MCHA, and exactly why it is a different regulatory, allergen and customs proposition. MCHA is bovine, never vegan or vegetarian, needs BSE/TSE country-of-origin and fitness-for-human-consumption documentation on every lot, and is closed out of some halal and kosher programmes. Regulatory fit is where deals are lost, so check it before ordering. Annex II of EU Directive 2002/46/EC lists calcium sources by name and includes calcium salts of orthophosphoric acid; a synthetic hydroxyapatite reads onto that entry far more comfortably than a whole-bone concentrate carrying collagen does, and buyers shipping MCHA into the EU should take their own regulatory advice rather than assume. Supplement-grade material is commonly controlled against the tribasic calcium phosphate compendia — the Food Chemicals Codex monograph assays 34.0–40.0% calcium and describes a variable mixture approximating 10CaO·3P2O5·H2O, which is the same chemistry family and is why food-grade tricalcium phosphate and hydroxyapatite are so often confused. Fluoride, arsenic and lead limits from the applicable monograph should be written into the purchase specification; fluoride in particular concentrates in bone, so it is the analysis to insist on for MCHA. Thovek states composition and nutrient function only and makes no therapeutic claim.