@diane0329
Hi Diane,
This is actually a discussion held regularly on Inspire Osteoporosis site.

Firstly, let me say that I use calcium supplements as needed. I have gluten intolerance and do not always absorb my nutrients well, but I try not to over supplement so I also use Cronometer to track my food intake and supplements to see if and when I might need calcium aspartate (easier for me to absorb).

Now, calcium. Yes, what your friend is saying has research behind it. In fact, an entire book was written about the situation and how to remedy the possible problem called Vitamin K2 and the Calcium Paradox: How a Little-Known Vitamin Could Save Your Life.

But yes, too much or little absorbed calcium may end up in your arteries, almost like a bone build up. And also in order to absorb calcium, adequate vit d is needed. Indeed, without adequate vit d only about 10–15% of dietary calcium is absorbed, I am sure that your doctor is checking those vit d levels for you.

Yet what to do to make sure that your calcium stays in your bones and not your cardio system? This is where vit k2 comes in. Vitamin K2 is essential for directing calcium into bones and away from the cardio system. Vit K2 does this by activating proteins that manage calcium metabolism. K2 also activates osteocalcin to build bones, as well as, Matrix GLA Protein, MGP, to prevent arterial calcification. High K2 intake, specifically MK-7, is linked to a 50% reduction in vascular calcification.
https://pmc.ncbi.nlm.nih.gov/articles/PMC4566462/.
https://menaq7.com/news/the-heart-health-nutrient-97-of-americans-are-missing-vitamin-k2s-role-in-cardiovascular-protection/.
etc. etc.

Indeed, Vit K2 is used in Japan as an osteoporosis treatment, entirely because of its ability to route calcium to the bones and away from the cardio system. Caveat, vit k2 should be oked by your doctor especially if you are on blood-thinning medications. In fact, I ask my doctor plus I run my supplements and medical conditions by copilot to make sure that I have no known problems with my other supplements or my few drugs. I have gluten intolerance so I take more supplements than some to be able to get my nutrients, but since stopping gluten that is improving and I am dropping supplements. So sometimes my health is a moving target that needs an AIs help to juggle all the potentialities.

Another thing to consider is that the body may only absorb 500 mg at a time of calcium then the rest is secreted or goes places where you don't want it to go. So if you do decide to supplement with calcium, based on your doctor's recommendations and after checking your diet/supplements on cronometer, then do so in just 500 mg doses at a time. Also, ask your doctor about adding in Vit k2 in an appropriate amount for you and your body.

Now once the research and studies are out of the way then the question arises, if I take calcium and vit k2 to help protect my cardio system what kind of K2? This is where most of the discussion has arisen in the Inspire community. Mk7 or mk4 and how much? Mk7 makes the most logistical sense and depending on cronometer results for your diet the range may run from 180 to 360 micrograms, another good question for your doctor to check within your medical history context.
Discussions about Vit K and some other supplements, what Inspire posters use and why:
So I tried to take all those discussions and replies and put them into a compilation post and here are several:
Vitamin K:
https://www.inspire.com/groups/bone-health-and-osteoporosis/discussion/mk-4-mk-7-and-osteoporosis/
https://www.inspire.com/groups/bone-health-and-osteoporosis/discussion/vitamin-k-supplement-what-kind/
https://www.inspire.com/groups/bone-health-and-osteoporosis/discussion/vit-k-again-a-danger-or-needed-for-osteoporosis-patients/
A general post of various supplements for bone health:
https://www.inspire.com/m/Kathleen1314/journal/7ed0c4-supplements-calcium-vit-k-collagen-etc/
I hope this helps, happy researching! 🙂