It needs to be only small enough to swallow. It is easily reduced when it hits the very strong acid in the stomach. Most "absorption" is by such chemical reaction and not a mechanical entry into the blood if it is small enough. For example, some fibers can be ground as fine as you want and they still pass from the gut because they are not very subject to the chemistry required for absorption. Some retail calcium pills come from shells.
Quoted message said:
I read that ground eggshells are a dietary source for calcium. How finely must it be ground for absorption and how much calcium would it have? regards andrew vecsey
