Vitamin D (specifically D3, the form you get from the sun) is essential for proper calcium absorption. Without D3, you may be missing out on benefits from the calcium in your diet.
While vitamin D ensures calcium is absorbed, vitamin K2 (specifically as MK-7, the most bioavailable form) directs it to bones instead of arteries, where calcification or other issues could occur.
ULTRA CAL is a calcium supplement used to magage calcium deficiency and can be helpful to those with calcium deficient diets or where the bodies need for calcium out weighs calcium intake. It contains Nano calcium, and MCHA microcrystalline calcium, combined with the co-factors Vitamin K2 and D3 and other minerals to help provide and support the absorption of calcium.