I looked up the number and it is currently listed at about
25% (PDF) for the US. Depending on whether we get better at fighting heart disease, cancer, or other diseases, that number will rise or fall. It is high right now because of the reduction of deaths due to accidental causes or simple infections.
Not to mention other diseases, that used to kill people, such as measles, whopping cough, small pox, pneumonia,
cholera, typhoid, tuberculosis, etc., etc., etc.!