Cell Regeneration Slows to a Crawl As We Age

You’re feeling pretty good about yourself. You exercise. You watch what you eat. Your parents lived into their 80s, and your children insist you’re going to beat that and live to be 100.

Now consider:

With each passing day, your heart muscle thickens and your arteries stiffen. Your breathing capacity declines and your brain gradually loses its ability to remember, say, where you put your car keys.

What’s more, each of the more than 10 trillion cells in your body sustains damage 50,000 to 100,000 times every day from aggressive compounds, many of which your body produces in the normal course of living. Keeping in mind that survival depends on your body’s ability to repair and regenerate cells, that disconcerting fact is enough to make you say to heck with it and reach for the brownies.

Welcome to the world of aging, where the unavoidable processes within our body combine with our sometimes-detrimental lifestyles to lead us ever closer to life’s inevitable conclusion — death.

“It’s many, many different interactions between the environment and our gene pool that cause us to age,” says Dr. Jeffrey Ross, chairman of the pathology department at Albany Medical Center Hospital. “But one thing that’s absolutely a guarantee: To date, every human being that has been born has aged. It’s ubiquitous, not preventable currently, and has been demonstrated on everyone who has walked the planet.”

The good news

Fortunately, the news isn’t all grim. Humans are living longer than ever. Life expectancy in the United States has risen in the past century from 47 to 78. That promises to keep rising with continued advances in research, medical care and public awareness of healthy lifestyles.

Someone alive today will become the first human to live to be 150, says Steven Austad, one of the country’s foremost experts on aging and author of “Why We Age: What Science Is Discovering About the Body’s Journey Through Life.”

But first, that person, and the rest of us, must survive the constant assaults on our cells and the gradual deterioration of our body’s mechanisms for keeping us vital.

Aging involves every molecule, cell and organ in the body, and it’s not completely understood. But basically, the experts say, like the aging of a house or car, it’s a maintenance problem.

“What happens is, everything falls apart,” says Austad, professor of cellular and structural biology at the University of Texas Health Science Center. “If you think of us as something capable of repair when damage occurs inside our bodies, then what aging is, is the gradual failure of repair.”

Free radicals

One of the most vivid examples is how our bodies constantly battle a greedy molecule known as the oxygen free radical. Free radicals are a byproduct of burning oxygen in our cells. We ensure their production by eating food and breathing air. Pollution, radiation and cigarette smoke also produce free radicals.

When the body breaks down an oxygen atom during its production of energy, the reaction strips away an electron. Electrons are electrically charged particles that spin around atoms and molecules, usually in pairs.

Free radicals lack one electron, and that’s where the trouble starts. (Under certain conditions, however, free radicals do good things, such as help the body fight infection.) But now, unstable without its mate, it “steals” electrons from other molecules, in the process damaging DNA, the protein inside cells, and even the membrane-enclosing cells.

That damage accumulates in cells and tissues, triggering many of the changes that occur as we age, according to the National Institutes of Health. Free radicals have been implicated in nearly every major disease and malady.

“Everything in your cell is basically damaged by these oxygen radicals,” Austad says. “All that damage is repaired to a certain extent, just like when you get cut, it’s repaired to a certain extent. But it’s not repaired perfectly; you get a little scar.”

Breaking down

The unrepaired damage not only mounts, but the body’s ability to counteract free radicals also diminishes with age. Meanwhile, cells wear out and die. Other cells lose their ability to divide.

“You’ve got slightly different problems depending on whether you’re talking about the brain, the heart, the kidneys, the skin, the immune system,” Austad says. “The thing that unifies them all is that the cells are not working as well as you get older as they were when they were younger.”

This breakdown in cellular function compounds the maintenance problem and lessens the body’s ability to fight disease, leading to aging and, eventually, death. Although scientists have slowed the aging process in laboratory animals by altering genes associated with growth hormones and other procedures, they have yet to find ways to do it with humans.

“There’s nothing that we can really put our finger on right now to say ‘This is how to slow aging in people,’ Austad says. “But progress is moving along so many different directions now. It’s just a matter of time until we figure out what works for humans.”

Three part series begins today

We are living longer than ever before. And scientists are studying ways to keep us alive, healthy and active even longer. Starting today, we are launching a three-part series taking a look at human longevity.

Today we peek into the complicated process of aging, the science of how and why we age.

Tuesday we examine the major advances in medicine and changes in lifestyle that are allowing us to live longer.

And Wednesday we look for what you need to know to live to be 100, including tips from those who’ve made it.

Individuals age at extremely different rates. In fact even within one person, organs and organ systems show different rates of decline. However, some generalities can be made, based on data from the Baltimore Longitudinal Study of Aging.

HEART thickens with age. Maximal oxygen consumption during exercise declines in men by about 10 percent with each decade of adult life and in women by about 7.5 percent. This decline occurs because the heart’s maximum pumping rate and the body’s ability to extract oxygen from blood both diminish with age.

ARTERIES tend to stiffen with age. The older heart, in turn, needs to supply more force to propel the blood forward through the less-elastic arteries.

LUNGS maximum breathing capacity may decline by about 40 percent between the ages of 20 and 70.

BRAIN loses some of the structures (axons) that connect nerve cells (neurons) to each other as we age, although the actual number of neurons seems to be less affected. The ability of individual neurons to function may diminish with age.

KIDNEYS gradually become less efficient at extracting wastes from the blood (and bladder capacity declines).

BODY FAT gradually increases in adulthood until individuals reach middle age. Then it usually stabilizes until late life, when body weight tends to decline. As weight falls, older individuals tend to lose both muscle and body fat. With age, fat is redistributed in the body, shifting from just beneath the skin to deeper organs.

MUSCLE mass declines without exercise, an estimated 22 percent for women and 23 percent for men between the ages of 30 and 70.

BONE MINERAL is lost and replaced throughout life; loss begins to outstrip replacement around age 35. This loss accelerates in women at menopause. Regular weight-bearing exercise — walking, running, strength training — can slow bone loss.

EYES can have difficulty focusing close up, beginning in the 40s; the ability to distinguish fine details may begin to decline in the 70s. From 50 on, there is increased susceptibility to glare, greater difficulty in seeing at low levels of illumination, and more difficulty in detecting moving objects.

HEARING becomes more difficult in higher frequencies with age. Even older individuals who have good hearing thresholds may experience difficulty in understanding speech, especially in situations where there is background noise. Hearingdeclines more quickly in men than in women.

Source: http://www.nia.nih.gov