Bone remodeling — building vs preserving

What actually decides this outcome, in order of size

Bone mass is the running balance of two cell populations, and every intervention on this page pushes exactly one of them. Ranked by how much each moves that balance:

1. Sex steroid withdrawal, which is the event that starts most of this. Estrogen restrains osteoclast lifespan through the RANKL to osteoprotegerin ratio, so the years either side of menopause carry the steepest loss anyone experiences. In men the equivalent is the aromatase-derived estradiol fraction, not testosterone directly, which is why Estradiol, Sensitive (LC/MS-MS) matters in a male osteoporosis workup.
2. Mechanical strain, and it is not walking. High-intensity resistance and impact training in 101 postmenopausal women with osteopenia raised lumbar spine bone mineral density by 2.9% while controls lost 1.2% (P<0.001) Watson 2018. Osteocytes sense strain magnitude and strain rate; low-magnitude repetition maintains and does not build.
3. Whether a drug is indicated at all, and which class. In 4,093 postmenopausal women, 12 months of romosozumab 210 mg followed by alendronate produced new vertebral fractures in 6.2% (127 of 2,046) against 11.9% (243 of 2,047) on alendronate throughout (P<0.001), and clinical fractures in 9.7% against 13.0%, a 27% lower risk Saag 2017. That is the size of the anabolic-first decision, and no supplement is in that conversation.
4. The arithmetic of the remodeling unit itself. Osteoclastic resorption of one unit takes about 3 weeks; osteoblastic refill of the same cavity takes 3 to 4 months. That asymmetry is why an anti-resorptive raises measured density over the first 12 months mostly by closing the remodeling space rather than by building anything, and why an anabolic and an anti-resorptive cannot be judged on the same interval.
5. Vitamin D and parathyroid hormone adequacy, as a precondition. A raised PTH against a low 25(OH)D is secondary hyperparathyroidism, which is bone being dissolved to defend serum calcium. Correcting it is not a treatment for osteoporosis, it is the condition under which any treatment works.
6. Protein and body mass, which act through load. Bone responds to the strain its muscle imposes, so sarcopenia and osteoporosis progress together, and 1.2 to 1.6 g/kg/day of protein alongside resistance work is a bone intervention delivered through muscle rather than through calcium.
7. Calcium and the rest of the shelf, last and near zero. Across 33 trials and 51,145 community-dwelling adults, calcium or vitamin D was not associated with lower fracture incidence Zhao 2017.

The order to run these in, and what has to be true first

The sequence is the content of this pathway. Getting it backwards wastes the one drug class that builds bone.

1. Get the number before the argument. A DEXA T-score, plus any fragility fracture history, decides everything downstream. Without it this page is a list of mechanisms with no threshold attached.
2. Correct the substrate. Vitamin D (25-Hydroxy) and Parathyroid Hormone & Calcium read together, plus Osteocalcin as an index of osteoblast activity. Vitamin D where 25(OH)D is low, Calcium & Magnesium only to reach a total intake around 1000 mg/day from food plus supplement, and Vitamin K2 Complex because the vitamin K-dependent gamma-glutamyl carboxylase is what activates osteocalcin and matrix Gla protein.
3. Load, and keep loading. The 2.9% lumbar gain came from supervised high-intensity work, not from walking Watson 2018. Creatine at 3 to 5 g/day and Whey Protein (RecoveryPro) support the training rather than the bone directly, which is the honest way to file them.
4. Anabolic before anti-resorptive, where a drug is indicated. Teriparatide and Abaloparatide are PTH-receptor agonists that build; Raloxifene is a selective estrogen receptor modulator that preserves. Building on a skeleton whose remodeling has already been switched off produces less than building first and preserving after Saag 2017.
5. Know the skeletal half-life of what you start. Bisphosphonates bind hydroxyapatite and are released only as that bone is resorbed, giving a skeletal residence measured in years, which is why a drug holiday is a concept at all. Teriparatide and Abaloparatide are the opposite: daily subcutaneous peptides with a plasma half-life near an hour, a treatment ceiling around 24 months, and a gain that is largely lost within 12 months of stopping unless an anti-resorptive follows.
6. Then the substrate extras, knowing what they are. Collagen, Silica, Vitamin C as the cofactor for prolyl and lysyl hydroxylase, Boron and Bone Support. Cartalax and Sigumir are graded theoretical for this goal on this site's own tiering and should be read as such.

What gets bought for this that cannot move it

Strontium will make your next DEXA look better without making your bone stronger. Strontium has an atomic number of 38 against calcium's 20, so it attenuates X-rays far more per atom. Substituted into hydroxyapatite it inflates apparent bone mineral density on the exact measurement you are using to judge success. This is the clearest case on the whole site of a supplement moving the read-out rather than the outcome.

Calcium supplementation is not fracture prevention. 51,145 participants across 33 randomized trials say so, with a hip-fracture risk ratio for calcium of 1.53 (95% CI 0.97 to 2.42) Zhao 2017. Calcium is a precondition, and a precondition that is already met does nothing when you add more of it.

No supplement on this page is an alternative to a drug at a T-score of -3.0 or after a hip fracture. The comparison at that point is between an anabolic and an anti-resorptive, with a 27% difference in clinical fracture between two active drugs over 12 months Saag 2017. A year spent on substrate is a year of remodeling imbalance.

Collagen and Silica are substrate for the organic matrix, not for the mineral. Type I collagen is 90% of the organic phase of bone, and hydroxyapatite crystals nucleate on it, so the argument is real. It is also the half of bone that fails last: a fragility fracture is a mineral and microarchitecture problem, and no trial has shown an oral collagen dose changing a T-score.

And if you have never had a DEXA, the useful purchase is the scan. Bone is silent until it breaks; there is no symptom to track and no blood test that substitutes for the T-score. Buying this pathway before the scan is treating a diagnosis you do not have.

How you would know it was working, on a real read-out and a real timescale

Bone gives you one slow read-out and two fast ones, and the whole skill is not judging the slow one early.

• DEXA at 12 to 24 months, same machine, same operator. A remodeling cycle runs about 3 to 6 months, and scanner precision error is roughly 1 to 2%, so a genuine 2.9% gain Watson 2018 needs a year before it clears the noise. A repeat scan at 6 months answers nothing and costs the same.
• Osteocalcin at 3 to 6 months, as the early warning. Formation markers move within a single remodeling cycle. Rising osteocalcin on an anabolic is the expected direction; rising osteocalcin on an anti-resorptive means the drug is not being taken.
• Vitamin D (25-Hydroxy) and Parathyroid Hormone & Calcium at 8 to 12 weeks. Four to five half-lives of 2 to 3 weeks for 25(OH)D. A parathyroid hormone that falls as 25(OH)D rises confirms the deficiency was doing damage.
• Estradiol, Sensitive (LC/MS-MS) and Total Testosterone once, in any man with low bone mass. Male osteoporosis is secondary until proven otherwise, and the aromatized estradiol fraction is the one that acts on bone.
• CTX at 3 months if an anti-resorptive was started. The C-terminal telopeptide of type I collagen is the resorption marker, it falls by more than 50% within 3 months on an effective drug, and it swings 30 to 40% across the day, so it is drawn fasting before 9am or not at all.
• Height, annually, measured against a wall. A loss of more than 2 cm is a vertebral compression until imaging says otherwise, and it is free.

What will fool you. Strontium inflates DEXA. So does spinal osteoarthritis and aortic calcification overlying the lumbar spine, which is why the hip is the more honest site in an older reader. And a bone turnover marker drawn non-fasting, in the afternoon, can differ from a fasting morning draw by more than the treatment effect you are looking for.

Sources read for these sections

• Watson SL. High-Intensity Resistance and Impact Training Improves Bone Mineral Density and Physical Function in Postmenopausal Women With Osteopenia and Osteoporosis: The LIFTMOR Randomized Controlled Trial. Journal of Bone and Mineral Research 2018;33(2):211-220 · PMID 28975661
• Saag KG. Romosozumab or Alendronate for Fracture Prevention in Women with Osteoporosis. New England Journal of Medicine 2017;377(15):1417-1427 · PMID 28892457
• Zhao JG, et al. Association Between Calcium or Vitamin D Supplementation and Fracture Incidence in Community-Dwelling Older Adults: A Systematic Review and Meta-analysis. JAMA, 2017 · PMID 29279934