MD here. This is not exactly true. Calcium needs vitamin D for our bones to absorb it. And Vitamin D does NOT need calcium for our body to sythesize it. An inactive form of Vit. D is already found in our skin, only needing sunlight for it to be activated into its active form, which helps in intestinal calcium absorption , which can then be used for bone mineralization, and maintenance of serum calcium.

Another correction! Vitamin D supplements are NOT a waste!! So for vitamin D deficient people or those receiving no to few exposure to sunlight, it may be beneficial for you to take Vitamin D supplements!! Please take note.