Or you could take magnesium with the calcium. Magnesium regulates proper calcium absorbtion.
Actually it has to do with the action of vitamin d3 and vitamin k2 on a specific protein. One (d3) does ‘step one’, the other (k2) does ‘step two’. Both steps have to be completed or the calcium stays in the wrong places.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4566462/
“Vitamin D and K2 Work in Tandem to Slow Arterial Calcification
Story at-a-glance
Taking vitamin K2 along with vitamin D slowed the progression of arterial calcification, whereas vitamin D alone did not
Vitamin K2 engages in a delicate dance with vitamin D, and you need both in adequate amounts for optimal health
Vitamin D and vitamin K2 work together to produce and activate Matrix GLA Protein (MGP), which congregates around the elastic fibers of your arterial lining, guarding them against calcium crystal formation
If you take oral vitamin D, you need to also consume in your food or take supplemental vitamin K2
By Dr. Mercola
As I’ve discussed on numerous occasions, vitamin D is a critical nutrient for optimal health and is best obtained from sun exposure or a safe tanning bed.
However, many are taking oral vitamin D, which may become problematic unless you’re also getting sufficient amounts of vitamin K2.
Vitamin K2 engages in a delicate dance with vitamin D, and you need both in adequate amounts for optimal health. The importance of this was once again highlighted in a new study…
Vitamin D and Vitamin K2 Slow the Progression of Arterial Calcification
The study was designed to compare the effect of oral administration of vitamin K2 (MK-7) plus vitamin D, or vitamin D alone, on the progression of coronary artery calcification score and carotid intima media thickness (the lining of the main arteries in your neck that feed blood to your brain), which are hallmarks of potentially lethal heart disease and stroke.
The data revealed a slower progression of calcification in those taking both vitamin K2 and vitamin D compared to those taking vitamin D alone.1 The study’s lead author said:
“In this study, the K2 and D protected against cardiovascular calcification, while the D group alone did not. Clearly, this has positive implications for human health.”
This makes sense because whereas vitamin D provides improved bone development by helping you absorb calcium, there is new evidence that vitamin K2 directs the calcium to your skeleton, while preventing it from being deposited where you don’t want it.”
https://articles.mercola.com/sites/articles/archive/2013/10/19/vitamin-d-vitamin-k2.aspx