The Skin or Flesh is no Different than the Bones structure !
In other words for strong Dense Bones the body must have the needed Basic Alkaline Minerals , starting with Calcium, and then have the needed Alkaline Trace Minerals to Cause the Density and Strength to be made !
It may be like in the steel alloy business, it takes the Alkaline Trace Minerals to build the Density and Strength into the steel !
So for a thin skin to tear and bruise easily, would mean that the body was Lacking in the needed Alkaline Minerals including some of the Alkaline Trace Minerals !