The body is constantly changing, no matter what age. It has to maintain homeostasis, or balance at all times or illness/death occurs. If your body is weakened, it then becomes harder to maintain this state. If one component goes out of balance; ie, water content, it affects the whole body. Swelling(edema) CHF(serious heart problem) kidneys may be overtaxed/unable to release the extra fluid. As the body ages organs naturally become less efficient, therefore making homeostasis more challenging.