The conventional wisdom and common recommendation is to supplement with calcium, but I saw at least one study stating that it is not necessary: https://pubmed.ncbi.nlm.nih.gov/9584497/
I rather suspect that if you are already eating a diet deficient in calcium, breastfeeding may exacerbate the issue, and since the supplements tend to have a poor bioavailability, taking them even if you don't need to isn't going to be harmful. Eat a healthy balance of foods and you are probably fine.
I may have a nurse for a mother, but I am very much not a doctor.
> taking them even if you don't need to isn't going to be harmful
I think, the transporter for calcium is the same used for some other minerals. So, if you're not mindful (about timing), you may be competitively blocking the absorption of e.g. zinc, which is much more precious nutritionally - zinc is very important for immune function and healing, while deficiency is common.
Calcium supplements can cause constipation, which may be not very fun after giving birth... Not to mention the implications of (lack of) quality control in the supplement market, by proxy, for a rapidly developing human being. Which substances are part of the formulation, other than calcium salts? Does the adult portion of copper or X accumulate in a mother's milk?
Not saying, you shouldn't take calcium supplements. But really, any supplement can be harmful, if consumed without need or consideration. (Fun fact: Vitamin A supplementation increases lung cancer risk!)
I rather suspect that if you are already eating a diet deficient in calcium, breastfeeding may exacerbate the issue, and since the supplements tend to have a poor bioavailability, taking them even if you don't need to isn't going to be harmful. Eat a healthy balance of foods and you are probably fine.
I may have a nurse for a mother, but I am very much not a doctor.