This is an interesting topic, and one that concerns so many of us as we get older and our bones seem to age. I read recently that as many as half of women over 50 have osteopenia or osteoporosis.

We are all looking for the magical solution that will help, but there isn't ONE. We need to worry less about whether the calcium is from Tums, algae or anywhere else and look at the big picture and the science.

The big picture is that to protect our bones, we need proper diet including adequate protein and fat (other building blocks for cell reproduction.) We need consistent daily weight-bearing exercise or work, limited alcohol consumption and no smoking. Other health issues need to be considered, as many medications can interfere with bone production. Only if our diet does not provide enough calcium and micronutrients, or if our health requires medications which interfere with bone growth, does a supplement come into the picture.

The science is emerging. I found this recent report fascinating, in that it concentrated almost entirely on diet and nutrition, and only mentioned calcium supplementation as part of the nutrient analysis.
https://home.biomedpress.org/index.php/BMRAT/article/view/598
What I find troubling is that the makers of the brand name supplements have not submitted them to rigorous, scientific, randomized, double-blind, side-by-side testing with simpler products over a significant period of time (2 years or more) to demonstrate their superiority. Anecdotal studies are interesting, but they are not proof of superiority.

I have no problem if people feel more comfortable taking a higher-priced, nationally advertised supplement if they wish. However, I see way too many people spending money on expensive supplements and skimping on healthy foods because of their high cost. Or believing that "this one" is going to work where others have not.

Please look at the "Big Picture" and not the little pill in front of you.
Sue