Possible Clues:

• Element taken in supplements
• Element in bones
• White metallic element found in most animals and plants, Ca
• Essential constituent of bones and teeth
• Soft greyish-white metallic element
• Chemical element in bones, basis of lime
• By the sound of it, see a symbol for this
• You could make C a short for this
• Chemical element in bones and teeth
• Element, component of bones and teeth