Hydroxyapatite for Osteoporosis

Oral hydroxyapatite may slow bone loss slightly, but no trial has shown it prevents fractures, and it is not an established treatment for osteoporosis. Small trials of ossein-hydroxyapatite complex (OHC, hydroxyapatite combined with bone collagen and other proteins) and microcrystalline hydroxyapatite (MCH, called MCHC in the 1980s steroid trials) found less bone loss than calcium carbonate or no treatment, mostly in postmenopausal women. They mainly measured bone density and blood markers, and none showed fewer fractures (Castelo-Branco 2009; Ciria-Recasens 2011).

The best pooled result is a 2009 meta-analysis of 6 randomised trials, in which bone density changed 1.02 percentage points more with OHC than with calcium carbonate (95% CI 0.63 to 1.41) (Castelo-Branco 2009). That compares one calcium product with another, not with placebo, and most of the studies below were open-label. Guidelines put bisphosphonates first for postmenopausal women with osteoporosis (Qaseem 2023), so any hydroxyapatite would sit beside that treatment, not replace it.

The Endocrine Society guideline says nutritional and lifestyle measures and fall prevention should accompany every drug regimen (Eastell 2019). Calcium and vitamin D are covered on their own pages: calcium for osteoporosis and vitamin D for osteoporosis.

Hydroxyapatite is the mineral of bone: more than 99% of the body's calcium is stored as calcium hydroxyapatite in bones and teeth (NIH ODS). Taken by mouth, OHC and microcrystalline hydroxyapatite (MCH) work as calcium and phosphate supplements, and like other calcium supplements they lower bone turnover markers. In 100 women with a mean age of 71, MCH and conventional calcium (citrate or carbonate, 1 g of calcium a day) produced comparable falls in the resorption marker CTX and the formation marker PINP at 3 months. MCH raised ionised calcium less than the conventional calcium, though it raised phosphate and the calcium-phosphate product (Bristow 2014).

In 153 osteopenic women with low calcium intake, 500 mg a day of calcium as OHC lowered osteocalcin by 12.3% from baseline at 6 months and tricalcium phosphate by 9.9%, significantly more than placebo (Albertazzi 2004).

OHC also contains collagen and non-collagen proteins. One trial's analysis reported IGF-I, IGF-II, TGF-beta and osteocalcin in the product (Rüegsegger 1995). No trial we found separated those proteins from the mineral, or showed that they survive digestion and act on bone.

The 2020 study gave the OHC group 712 mg of calcium a day and the calcium carbonate group 1,000 mg, and its authors say the difference may be linked to the ossein (Castelo-Branco 2020). A rise in osteocalcin in one OHC arm was read as an anabolic effect, but osteocalcin is a blood marker, not bone strength (Ciria-Recasens 2011).

No dose has been shown to prevent fractures. The studies used OHC at 3.32 g a day, taken as 1,660 mg every 12 hours, for 1 to 4 years (Castelo-Branco 1999, two-year trial; Fernández-Pareja 2007). Given as two 830 mg tablets every 12 hours, that dose supplied 712 mg of elemental calcium a day in women over 65 with osteoporosis, who also took calcifediol (Ciria-Recasens 2011). One older trial gave OHC supplying 1,400 mg of calcium a day, about twice as much, for 20 months (Rüegsegger 1995). Women took MCH, or 1 g of calcium a day as citrate or carbonate, or placebo for 3 months (Bristow 2014), and MCHC was given at 6 to 8 g a day for 12 months to patients taking prednisolone (Pines 1984).

Count the elemental calcium, not the product weight, because the forms of calcium in supplements contain varying amounts of elemental calcium. Across food and supplements, the NIH recommends 1,200 mg a day for women over 50 and sets an upper limit of 2,000 mg a day from age 51 (2,500 mg for ages 19 to 50) (NIH ODS).

A 2009 meta-analysis identified 18 controlled trials and pooled 6 randomised trials comparing OHC with calcium carbonate on trabecular bone density. Bone density changed 1.02 percentage points more with OHC (95% CI 0.63 to 1.41; P < 0.00001) with no significant heterogeneity, and a sensitivity analysis agreed (Castelo-Branco 2009).

A 2015 review by the same lead author reached the same conclusion and says OHC may also ease pain and speed fracture consolidation in people with osteopenia or osteoporosis (Castelo-Branco 2015). Its abstract lists contact with companies that market the supplements among its data sources, and gives no figures for the pain or fracture-healing claims.

The best-controlled trial in established osteoporosis was small. Forty women were randomised, double-masked, to 1,400 mg of calcium a day as OHC or calcium carbonate for 20 months, and trabecular bone loss was 0.8% with OHC and 1.8% with calcium carbonate, a significant difference (Rüegsegger 1995). In 60 postmenopausal women who refused hormone therapy, an open study found no significant bone change on OHC over 2 years, while the calcium carbonate group lost 3.7% in year 2 and untreated women lost 3.5% and 5.6% at the first and second measurements (Castelo-Branco 1999, two-year trial).

In 120 women over 65 with osteoporosis, an open-label trial of OHC against calcium carbonate (both with calcifediol) found a larger rise in osteocalcin with OHC. Lumbar spine density fell 1.1% with OHC and 2.3% with calcium carbonate, while femoral neck density rose 2.5% and 1.2%. Only 54 of 120 women completed 3 years, and the abstract gives no P value for the density changes (Ciria-Recasens 2011).

In 118 women after surgical menopause (96 completed one year), OHC added to transdermal estradiol raised bone mineral content by 4.7% (P < .01), more than either treatment alone, in an open study (Castelo-Branco 1999, hormone therapy). In 90 women taking raloxifene, an ultrasound measure of bone fell by 18.72 m/s with OHC and 63.64 m/s with calcium carbonate over up to 3 years (P = 0.006), in an open-label study that used ultrasound rather than DXA (Pelayo 2008). These show OHC alongside other treatments, not that it adds fracture protection.

A non-randomised, open-label study of 851 perimenopausal women (T-score of -2 or higher, so none met the usual osteoporosis threshold of -2.5) found lumbar spine density stable on OHC and down 3.1% on calcium carbonate over 3 years (p < 0.001). Adverse reactions were more frequent with calcium carbonate (7.7% vs 2.7%) (Castelo-Branco 2020). A retrospective 4-year follow-up of 112 osteopenic women on OHC, with no control group, found forearm trabecular T-scores rising from -1.27 to -0.86 (Fernández-Pareja 2007).

In 36 people with chronic active hepatitis taking corticosteroids, 2 years of MCHC halted the fall in radius bone mineral content, and the loss of iliac crest cortical thickness was smaller (P < 0.025); back pain and fractures were uncommon and did not differ significantly (Stellon 1985). In 40 patients taking prednisolone 5 to 20 mg a day, 32 given 6 to 8 g of MCHC for 12 months had a marked fall in back pain (P < 0.001) against 8 untreated patients, and smaller losses of bone thickness that came close to significance (Pines 1984). Both trials are from the 1980s; Pines used untreated controls, and neither abstract describes blinding.

The American College of Rheumatology strongly recommends drug treatment for adults on more than 3 months of glucocorticoids who are at medium, high or very high fracture risk, choosing among bisphosphonates, denosumab and parathyroid hormone analogs (Humphrey 2023). Hydroxyapatite is not on that list.

The one placebo-controlled trial of OHC enrolled 153 osteopenic women on 500 mg of calcium a day. Bone-density changes did not reach statistical significance at 6 months, although OHC raised spine density 0.8% at 12 months in the women taking it. On bone turnover markers the authors judged OHC only slightly superior to tricalcium phosphate (Albertazzi 2004). In a placebo-controlled trial of 100 women, microcrystalline hydroxyapatite and calcium citrate-carbonate lowered bone turnover markers by comparable amounts (Bristow 2014).

Response is uneven. In women after oophorectomy, markers stayed lower than in controls in only half the treated patients after 3 years, and 13 further women had a transient response followed by accelerated bone loss (Stĕpán 1989).

Castelo-Branco C co-authored the meta-analysis, the review and three of the individual studies, so the pooled result is not independent. Trials by other groups (Rüegsegger 1995, Stĕpán 1989, Albertazzi 2004, Bristow 2014) were small or old and used different designs. No study measured fractures as its main outcome, compared hydroxyapatite with a bisphosphonate, or was a placebo-controlled trial with bone density as the main outcome in people with osteoporosis. We also found no human osteoporosis trial of nano-hydroxyapatite taken by mouth.

Calcium supplements in general have weak fracture data. A 2026 BMJ meta-analysis of 69 trials (153,902 participants) found little to no benefit on fractures: any fracture risk ratio 0.91 for calcium alone (95% CI 0.81 to 1.01, moderate certainty) and 0.91 for calcium plus vitamin D (0.84 to 0.99) (Massé 2026). A 2017 meta-analysis of 33 trials in 51,145 community-dwelling adults over 50 found no significant association with hip, vertebral or total fractures (Zhao 2017), and a 2015 review found a total-fracture risk ratio of 0.89 (95% CI 0.81 to 0.96) but no effect at any site in the four trials at lowest risk of bias (Bolland 2015). See calcium for osteoporosis for that evidence.

In the studies, OHC was generally well tolerated. Mild constipation affected 3.2% of 112 women over 4 years (Fernández-Pareja 2007), adverse reactions were reported in 2.7% of women on OHC against 7.7% on calcium carbonate in the 2020 study, mostly gastrointestinal (Castelo-Branco 2020), and in the placebo-controlled trial both OHC and tricalcium phosphate were well tolerated and did not differ from placebo for side effects (Albertazzi 2004).

It is still a calcium supplement. The NIH notes that calcium can cause gas, bloating and constipation, that higher supplemental calcium might increase the risk of kidney stones, and that according to some research calcium supplements might raise cardiovascular risk; hypercalcemia usually results from cancer or primary hyperparathyroidism (NIH ODS). Microcrystalline hydroxyapatite also raised blood phosphate and the calcium-phosphate product more than calcium citrate-carbonate in older women (Bristow 2014); the abstract does not say whether that matters clinically, but it is a reason for people with kidney disease to ask first.

Lead has been found in some calcium products. A 1993 analysis of 70 brands, including bone meal, found lead from 0.03 to 8.83 micrograms per gram, and about 25% of products exceeded the FDA provisional tolerable daily intake for children aged 6 and under (Bourgoin 1993). In 2000, lead was measurable in 4 of 7 oyster-shell and 4 of 14 refined calcium carbonate products (Ross 2000). We found no lead data for OHC or MCH products, so look for third-party testing.

The interaction that matters most for osteoporosis is with oral bisphosphonates, the first-line treatment. Hydroxyapatite is a calcium product, so the calcium interactions in the NIH fact sheet apply, although none was tested with OHC or MCH specifically (NIH ODS).