The Way We Age Now

[Guest guest]

Relevant to recent discussions regarding aging:

The Way We Age Now

http://www.newyorker.com/reporting/2007/04/30/070430fa_fact_gawande?

currentPage=1

Medicine has increased the ranks of the elderly. Can it make old age

any easier?

Extracts provided:

The hardest substance in the human body is the white enamel of the

teeth. With age, it wears away nonetheless, allowing the softer,

darker layers underneath to show through. Meanwhile, the blood supply

to the pulp and the roots of the teeth atrophies, and the flow of

saliva diminishes; the gums tend to become inflamed and pull away

from the teeth, exposing the base, making them unstable and

elongating their appearance, especially the lower ones. Experts say

they can gauge a person's age to within five years from the

examination of a single tooth—if the person has any teeth left to

examine.

Scrupulous dental care can help avert tooth loss, but growing old

gets in the way. Arthritis, tremors, and small strokes, for example,

make it difficult to brush and floss, and, because nerves become less

sensitive with age, people may not realize that they have cavity and

gum problems until it's too late. In the course of a normal lifetime,

the muscles of the jaw lose about forty per cent of their mass and

the bones of the mandible lose about twenty per cent, becoming porous

and weak. The ability to chew declines, and people shift to softer

foods, which are generally higher in fermentable carbohydrates and

more likely to cause cavities. By the age of sixty, Americans have

lost, on average, a third of their teeth. After eighty-five, almost

forty per cent have no teeth at all.

Even as our bones and teeth soften, the rest of our body hardens.

Blood vessels, joints, the muscle and valves of the heart, and even

the lungs pick up substantial deposits of calcium and turn stiff.

Under a microscope, the vessels and soft tissues display the same

form of calcium that you find in bone. When you reach inside an

elderly patient during surgery, the aorta and other major vessels

often feel crunchy under your fingers. A recent study has found that

loss of bone density may be an even better predictor of death from

atherosclerotic disease than cholesterol levels. As we age, it's as

if the calcium flows out of our skeletons and into our tissues.

To maintain the same volume of blood flow through narrowed and

stiffened blood vessels, the heart has to generate increased

pressure. As a result, more than half of us develop hypertension by

the age of sixty-five. The heart becomes thicker-walled from having

to pump against the pressure, and less able to respond to the demands

of exertion. The peak output of the heart decreases steadily from the

age of thirty. People become gradually less able to run as far or as

fast as they used to, or to climb a flight of stairs without becoming

short of breath.

Why we age is the subject of vigorous debate. The classical view is

that aging happens because of random wear and tear. A newer view

holds that aging is more orderly and genetically driven. Proponents

of this view point out that animals of similar species and exposure

to wear and tear have markedly different life spans. The Canada goose

has a longevity of 23.5 years; the emperor goose only 6.3 years.

Perhaps animals are like plants, with lives that are, to a large

extent, internally governed. Certain species of bamboo, for instance,

form a dense stand that grows and flourishes for a hundred years,

flowers all at once, and then dies.

Today, the average life span in developed countries is almost eighty

years. If human life spans depend on our genetics, then medicine has

got the upper hand. We are, in a way, freaks living well beyond our

appointed time. So when we study aging what we are trying to

understand is not so much a natural process as an unnatural one.

Inheritance has surprisingly little influence on longevity.

Vaupel, of the Max Planck Institute for Demographic Research, in

Rostock, Germany, notes that only six per cent of how long you'll

live, compared with the average, is explained by your parents'

longevity; by contrast, up to ninety per cent of how tall you are,

compared with the average, is explained by your parents' height. Even

genetically identical twins vary widely in life span: the typical gap

is more than fifteen years.

If our genes explain less than we imagined, the wear-and-tear model

may explain more than we knew. Leonid Gavrilov, a researcher at the

University of Chicago, argues that human beings fail the way all

complex systems fail: randomly and gradually. As engineers have long

recognized, many simple devices do not age. They function reliably

until a critical component fails, and the whole thing dies instantly.

A windup toy works smoothly until a gear rusts or a spring breaks,

and then it doesn't work at all. But complex systems—power plants,

say—have to survive and function despite having thousands of critical

components. Engineers therefore design these machines with multiple

layers of redundancy: with backup systems, and backup systems for the

backup systems. The backups may not be as efficient as the first-line

components, but they allow the machine to keep going even as damage

accumulates. Gavrilov argues that, within the parameters established

by our genes, that's exactly how human beings appear to work. We have

an extra kidney, an extra lung, an extra gonad, extra teeth. The DNA

in our cells is frequently damaged under routine conditions, but our

cells have a number of DNA repair systems. If a key gene is

permanently damaged, there are usually extra copies of the gene

nearby. And, if the entire cell dies, other cells can fill in.

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Carruthers

Wakefield, UK