Thanks for the answer I wasn't loosing sleep over it but its good to know!!
If it is calcium lactate, that is not what is in paint. Chalk is calcium carbonate, and can appear in many forms such as marble, limestone etc. Calcium is an element, which as Dave says, is necessary for bones, and probably many other things in the human body.
Not technically true, the chemical calcium lactate, Ca(C3H5O3)2 .5H2O, is found in milk, and can be added to skimmed milk. Calcium, as a form of chalk, is also used in white emulsion paints. But why worry. You drink water. Ships sail about the seas in water. It's just a different scare story. You need calcium, your bones would fall apart without it.