War of attrition

The human body can endure a stunning amount of wear and tear, but we have a job to do, too

human body

Feeling a bit old?

Could your body be telling you something about the wear and tear accumulated over the years?

Let’s look at a hypothetical man who is celebrating his 80th birthday. Even if he has shunned exercise during his entire life, his feet have absorbed the stress of more than 100 million steps.

His stomach and digestive tract have accepted and digested more than 30 tons of food. (In my own case, this would include about one ton of chocolate chip cookies.)

His heart muscle has contracted 3 billion times and his lungs have sucked in enough air to fill 1,000 blimps.

Consider the kidneys of this man. By age 80, they’ve filtered 4.5 million quarts of water, and tons of chemicals, from his blood.

The man has made a lot of trips to the bathroom, but his kidneys have been much busier than the amount of produced urine would suggest.

Ninety-nine percent of the filtered water has been reabsorbed by the kidneys’ collecting ducts, leaving about 65,000 quarts of urine that he’s had to eliminate.

Over his 80 years, the liver of our hypothetical man has produced hundreds of billions of chemical molecules needed to sustain his body’s metabolic processes, and it’s also destroyed billions of potentially toxic molecules.

And his brain has been vigilant, 24 hours a day, controlling not only every bodily function, but also his entire life.

Physical forces

It’s no secret that our bodies give out over time. Even if we avoid serious illness and disease, only 1 percent of us will live to age 100. And no one will live beyond age 110.

Advances in medical science have allowed more of us to live longer, but they haven’t extended our maximal possible life span.

Why do our bodies eventually fail? Lots of scientific theories exist, but the wear-and-tear theory is the most popular.

Since we’re accustomed to seeing things wear out over time (cars, refrigerators, clothes), it’s also the easiest to understand.

The wear-and-tear theory of human aging puts much of the blame on our physical environment: Like tires that wear out because of continued friction against the road, humans wear out by continued exposure to innumerable physical and environmental forces.

But what else?

Aging experts recognize that human senescence involves more than just wear and tear. Heredity plays a signifi- cant role.

Our complex genetic inheritance can explain why some of us live longer than others and why some of our individual body parts avoid the effects of wear and tear better than others. Some researchers believe we wouldn’t live beyond 110 years old even if we were blessed with the best of genes and somehow could avoid wear and tear.

They believe the natural replication and duplication of cells in our body — occurring on a daily and sometimes hourly basis to replace dying cells — is intrinsically an imperfect process. Eventually the life span of the new cells falls below the rate at which they can be replaced.

Accepting and adapting

We’re reminded every day that others consider us to be older adults. Our mailboxes are full of stuff promoting Medicare supplement insurance, estate planning, hearing aids, funeral arrangements and retirement apart- ments.

And the nice girl at the checkout counter offers us the senior discount.

Our bodies also remind us that we’re older adults — far too often.

Successful aging involves accepting and adapting to changes in our bodies and in our lives. But it also involves fighting back.

Exercising, eating right, staying off stools and ladders, having regular check-ups, and making new friends are just five of the 100 ways to fight back that I would discuss if I wrote a How to Live Longer book.

But the book really isn’t needed. We already know what to do.

The problem is doing it.

Dr. Michael Spilane, now retired, spent more than four decades practicing and teaching geriatric medicine in St. Paul. Send comments or questions to [email protected].