Calcium from plants might be OK
A 7-Year Longitudinal Trial of the Safety and Efficacy of a Vitamin/Mineral Enhanced Plant-Sourced Calcium Supplement.
J Am Coll Nutr. 2016;35(2):91-9. doi: 10.1080/07315724.2015.1090357. Epub 2016 Feb 17.
Kaats GR 1, Preuss HG 2, Stohs S 3, Perricone N 4.
1a Integrative Health Technologies, Inc. , San Antonio , Texas (G.R.K.).
2b Department of Biochemistry , Georgetown University Medical Center , Washington , DC (H.G.P.).
3c Creighton University , Frisco , Texas (S.S.).
4d Transdermal Biotechnology, Inc. , Meriden , Connecticut (N.P.).
The Magnesium, Vit D, Vit K, and Boron also help build bones, and MAY reduce other problems no consensus on Strontium
Note: Trial used 2 capsules taken twice a day - at a cost of $2.32Competing products using very similar ingredients are about 1/4 that priceSee also Vitamin D Life* Vitamin D Cofactors in a nutshell* Calcium supplements proven to NOT reduce fractures, but are proven to INCREASE heart problems – July 2015* Healthy bones need: Calcium, Vitamin D, Magnesium, Silicon, Vitamin K, and Boron – 2012* Calcium supplementation associated with 3.9X increase risk of atrial fibrillation – June 2015* Increased Vitamin K2 reduces the problems of excess Calcium – Nov 2013* Interactions between Magnesium, Vitamin D, and Calcium – April 2016* Death by Calcium, book by Thomas Levy – Dec 2013* * Calcium and Vitamin D category listing has items along with related searches** See also web* https://www.algaecal.com derived from a marine algae, 2 caps twice a day with meals* vitamin D3, vitamin K2, boron, and additional magnesium have been added to the algae powder to make AlgaeCal Plus 
See also Amazon (Jan 2018) - Vegan Calcium, Mg, Vit D, Vit K, and usually Boron, Silica, generally from algae* Doctor's Best 3 capsuies $0.18/day * [Nature's Way Alive!® Calcium Bone Formula Supplement](https://www.amazon.com/Natures-Way-Calcium-Formula-Supplement/dp/B007RMK3RY/ref=sr_1_4_a_it?ie=UTF8&qid;=1516724741&sr;=8-4&keywords;=calcium%2Balgae&th;=1) 3 capsules $0.76/day* [New Chapter Calcium Supplement with Vitamin K2 + D3 - Bone Strength Clinical Strength Plant ](https://www.amazon.com/New-Chapter-Calcium-Supplement-Vitamin/dp/B002BSH3HC/ref=sr_1_5_a_it?ie=UTF8&qid;=1516724741&sr;=8-5&keywords;=calcium%2Balgae&th;=1) 3 capsules $0.78/day* [Alive Calcium Bone Formula (Algaecal)](https://www.amazon.com/Alive-Calcium-Bone-Formula-Algaecal/dp/B00H58X6VU/ref=sr_1_4_a_it?ie=UTF8&qid;=1516727021&sr;=8-4&keywords;=AlgaeCal&th;=1) 4 capsules $0.82/day* [NATURELO Bone Strength - with Plant Calcium, Magnesium, Vitamins C, D3, & K2 ](https://www.amazon.com/NATURELO-Bone-Strength-Whole-Food-Supplement/dp/B0716RWHX4/ref=sr_1_28_a_it?ie=UTF8&qid;=1516722382&sr;=8-28&keywords;=calcium+vegan) 4 capsules $0.88/day* [Garden of Life Raw Calcium Supplemen](https://www.amazon.com/Garden-Life-Raw-Calcium-Supplement/dp/B003L31NM2/ref=sr_1_1_a_it?ie=UTF8&qid;=1516724957&sr;=8-1&keywords;=calcium%2Balgae&th;=1) 4 capsules $1/day* [Pure Synergy Bone Renewal ](https://www.amazon.com/Pure-Synergy-Capsules-Plant-Based-Magnesium/dp/B008HFUIAM/ref=sr_1_21_a_it?ie=UTF8&qid;=1516724746&sr;=8-21&keywords;=calcium+algae) 5 capsules $1.35/day Note: the above are just a few of the products available which have enough quantity of ingredients to be useful.📄 Download the PDF from Vitamin D Life
OBJECTIVES:
The objective of this study was to examine the safety and efficacy of a vitamin-mineral enhanced plant-sourced calcium AlgaeCal calcium (AC) in female consumers who had taken the supplement from 1 to 7 years.
METHODS:
Consumers who had completed at least one dual-energy x-ray absorptiometry (DEXA) bone mineral density (BMD) scan (N = 172) and/or blood chemistry test (N = 30) and purchased AC from 1 to 7 years were contacted and offered complimentary repeat tests. Safety and efficacy were examined by annualized changes in a 45-measurement blood chemistry panel and changes in BMD.
RESULTS:
No adverse effects or safety concerns were found in any of the annualized within-group annualized changes in the 45 blood chemistries or in between-group changes in a similar control group (n = 5070) who completed the same measurements. With regard to BMD, consistent and statistically significant within-group increases were found for the 7-year study period and when compared to expected BMD changes in 3 large databases or the combination (N = 25,885) of the 3 databases. Data from this study suggest that AC supplement was associated with a significant annualized and linear increase in BMD of 1.04% per year, 7.3% over the 7-year study period. These results stand in marked contrast to normative or expected changes of -0.4%/y from 3 different databases or in a combination of all 3 databases (N = 16,289).
CONCLUSIONS:
No evidence was found in cardiovascular risk as measured by adverse changes in blood lipids, nor was any evidence found of a diminished efficacy over the 7-year study period because gains in BMD were consistent and linear over the 7-year study period, averaging 1.04% per year over the 7-year study. The results are also consistent with earlier short-term studies suggesting that this supplement can facilitate significant increases in total body BMD in contrast to studies suggesting that calcium supplements can only slow down age-related declines in BMD.
PMID: 26885697 DOI: 10.1080/07315724.2015.1090357