This bone-support combo delivers 1,000mg of **Calcium**, 400mg of **Magnesium**, and 15mg of **Zinc** alongside 400 IU of **Vitamin D3** — a formula that looks solid on the label but has a significant absorption gap. All three minerals use oxide or carbonate forms, which are the least bioavailable options. **Magnesium Oxide** absorbs at roughly 4%, meaning your body may only use a fraction of that 400mg. **Calcium Carbonate** requires stomach acid to break down, so you'll need to take it with meals.

**Vitamin D3** at 400 IU falls short of the 1,000–5,000 IU range supported by clinical consensus for maintaining healthy blood levels. Since vitamin D is essential for calcium absorption — without enough, your body absorbs only 10–15% of the calcium — this underdose limits the formula's primary purpose. The magnesium-D3 synergy is a plus in theory, since magnesium activates vitamin D, but both are held back by low dosing or poor form.

The 3-tablet serving size also means you're getting 1,000mg of calcium at once, well above the 500mg threshold where absorption drops off sharply. Splitting your dose across meals would help, but the label directs you to take all three tablets together.