A third theory on aging suggests that years of poor health habits contribute most to aging. Osteoporosis is a good example. Skin loses elasticity and becomes thinner with age, resulting in sagging and wrinkling. Fewer sweat glands are present, so temperature regulation is less efficient. The heart shrinks with age, and fatty deposits clog arteries.
Lungs lose some elasticity, so ventilation is reduced.
A reduced blood supply to the kidneys results in the kidneys becoming smaller and less efficient. The digestive tract may lose muscle tone but still absorbs nutrients efficiently. Normal aging results in the loss of few nerve cells. Short- term memory may decline, but overall cognitive skills remain. After age 50, there is a slow decline in the ability to hear higher frequencies, and the lens of the eye does not accommodate as well.