**Calcium** at 1,200 mg paired with 1,000 IU of **Vitamin D3** — the D3 is essential here because without it, your body absorbs only 10–15% of calcium. Together, these form the baseline combination for bone density support, backed by large clinical trials.

The slow-release format addresses a real absorption problem: your body can't process more than about 500 mg of calcium at once, so spreading the release over time helps you actually use more of it. You also get 80 mg of **Magnesium**, which your body needs to activate vitamin D — though at 80 mg, it's below the 100–400 mg supplemental range, so consider it a partial contribution rather than a full dose.

One notable absence is **Vitamin K2**, which helps direct calcium into your bones rather than your arteries. If you're taking high-dose calcium long-term, adding K2 is worth considering.