Let's say you are funneling chia seeds like it's your fucking JOB in order to get more calcium. Then you go to your doctor and find out you have a calcium deficiency. WHAT GIVES?
If you aren't getting a good amount of Vitamin D then all of your calcium building efforts will be in vain. In short: you need the D.
But the calcium/Vitamin D relationship isn't the only dependency here. The mos basic rule is that some vitamins are fat soluble, meaning that your body needs fat to absorb and dissolve them, and some are water soluble.
FAT SOLUBLE: Vitamin A, D, E and K
WATER SOLUBLE: Vitamin C, B1, B2, B3, B6, B12, Bitoin, Pantothenic Acid
The rest are trickier, so to make things easy I made you guys a chart:
Some credit goes to THIS website, some of the knowledge I've just acquired over the years.