That's because animal flesh is acidic, forcing calcium stored in the body (eg, in bones) to be drawn into the bloodstream to buffer the acid. (parsleyhealth.com)
In the bones, the hormone triggers the release of calcium stores from the bones to the blood. (hormone.org)
Breast milk is rich in calcium, and if your diet is lacking in this important nutrient, your body will use your own calcium stores, which could leave you deficient. (fitpregnancy.com)