Factors:
Over active cells that become cancerous
Sun damage
Those are the two main ones I know of
I see you don't have any answer listed. However, I'll add a few that I feel are important to achieve good physical fitness. The first key one would be exercise. We need to keep our body's blood moving as well as our joints, muscles, ligaments and bones all in good condition. When we do things such as cardio, aerobic exercises and those similar, it helps with our heart, lungs and various other things. Now, part two of this would be proper nutrition. We're unable to meet our full potential with our bodies if we only do one and not the other. Proper nutrition is key to maintaining a healthy body and needed just as much as exercising. Eating right will not only make us feel better but make our body better as well!
So, when you combine proper nutrition and exercise, anyone can achieve good physical fitness. Hope this helped!
