Calculate the bone stack — calcium + vitamin D + K2 + magnesium + protein — by age, sex, and risk factors. The 1,200 mg calcium-only era is over; modern bone health is a 4-5 cofactor question. Calculator helps avoid calcium-only over-supplementation (arterial calcification risk). Math, not medical advice.
Your situation
| Component | Daily target | Best form | Notes |
|---|
Why each cofactor matters
- Calcium — building block of hydroxyapatite. Without enough, body resorbs from skeleton.
- Vitamin D — required for intestinal calcium absorption. Without D, only 10-15% of dietary calcium absorbs (vs 30-40% with adequate D).
- K2 (MK-7) — activates osteocalcin (puts calcium IN bone) and matrix Gla protein (keeps calcium OUT of arteries). The “directional traffic cop.”
- Magnesium — required cofactor for vitamin D metabolism (multiple enzymes). Mg deficiency reduces D effectiveness. Also direct bone matrix component.
- Protein — collagen scaffold for bone. Adequate protein (~1.0-1.2 g/kg in older adults) is essential. Under-protein is a hidden cause of fragility fractures.
- Strontium, boron, silicon — minor trace minerals with some evidence. Generally adequate from diverse diet.
The calcium-from-food preference
Multiple lines of evidence suggest dietary calcium is safer than supplemental calcium at the same dose:
- Dietary calcium is absorbed gradually with meals; supplement calcium is a bolus.
- Dietary calcium comes with cofactors (protein, Mg, K from dairy/greens).
- Bolland 2010 meta-analysis suggested supplemental calcium (but not dietary) may modestly increase CV events.
- Aim to fill the dietary-RDA gap with supplement, not replace dietary calcium.
- Best food sources: dairy (~300 mg/cup milk), kale (~100 mg/cup cooked), sardines (~325 mg/3oz), tofu (calcium-set, ~250 mg/half cup), almonds (~75 mg/oz), fortified plant milks (~300 mg/cup).
Best calcium supplement forms
- Calcium carbonate: cheapest, 40% elemental Ca. Take with meals (needs stomach acid). Avoid with PPIs.
- Calcium citrate: better absorbed (especially on empty stomach or with PPIs). 21% elemental Ca.
- Calcium hydroxyapatite (microcrystalline): from bone meal, mimics bone composition. Premium positioning.
- Calcium gluconate / lactate: low elemental %, larger pill burden.
- Algae-based calcium (AlgaeCal): markets clinical trials showing bone density improvements — limited independent replication.