Stop using drugs. :) hope that helped!
It's not hard to keep yourself healthy and in shape. the two most important things to keep yourself healthy is exersice and an appropriate breakfast. It's not nesessary to run a marathon or do a deep workout. A light jog is enough to keep you health everyday. Breakfast is important to keep your mind functioning properly. Making healthy life choices is also important.
Deficit of insulin, higher levels of glucose
Only one sperm cell makes it to the ovum
How badly the person is injured (how deep the cut or how bad the tear) and their body type.