iAge

Changing how we see aging

How Old Are You?

Our bodies are in a constant frenzy of renewal

Just under 11 years old should be the answer. Seriously. Biologically our body averages about 11 years old.

Jonas Frisen, a stem cell biologist at the Karolinska Institute in Stockholm developed a method for determining the age of each organ. Although some cells remain with us the duration of our life--neurons of the cerebral cortex, cells of your inner lens in our eyes, muscle cells of your heart—the rest of our body is in a constant frenzy of change and rejuvenation.

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Even our brain changes and renews itself. Joseph Altman first discovered brain cell regeneration—or neurogenesis—in 1962. Recently Elizabeth Gould of Princeton University, reported that each day's memories might be recorded in the neurons generated that day. Our brain might be going through daily renewal and change. With white matter in the brain—the predominant matter—renewing itself faster then the grey matter—which just covers the surface of the cortex. While all these changes are going on in the brain everything else is changing and renewing itself.

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The youngest part of our body is our intestines that are only 2-3 days old, while our taste buds replenish themselves every ten days. Then within weeks, our skin and lungs completely replenish themselves (2-4 weeks). Every few months our liver is replaced (5 months) and nails (6-10 months). Then every four months, after travelling over 300 miles and going through the heart 170,000 times, 60 times per hour our red blood cells are given respite and are renewed.

Our annual makeover includes new hair (for those that have hair, every 3-6 years) new bones (every 10 years) and lastly, most of our heart (every 20 years).

So the question is why do we look so old if we are only 11 years old?

This is the central question in gerontology. As we renew each organ in our body—and we chronologically age—the rate of change decreases and we get more errors in new cells. There are many possible reasons for this, and all could apply. It could be that our genetic material gathers faulty changes and its information becomes gradually degraded. Like a cassette tape that is repeatedly copied.

It could also be because the cells themselves becomes less efficient at cleaning after themselves leaving behind them a lot of cellular trash. It could be that our stem cells—that exist even in older adults—eventually become less efficient with age as they are bombarded with toxins, harmful rays and temperature changes. Sometimes when we damage an organ—for example damaging our lungs by smoking—the scaring tissue cannot be renewed and replaced. We in effect stop our body from staying young.

This is why looking younger also means that you are younger and live longer. In the Danish Twin study Axel Skytthe and his colleagues reported that among monozygotic twins who share the same genes—the twin that looked younger is more likely to live longer. But there are no short cuts. Undergoing plastic surgery does not result in longer life because there is also the Hayflick Limit…each of our 30 trillion cells in our body has a time bomb. At some point the cells reach their own individual lifespan and stop reproducing.  

© USA Copyrighted 2014 Mario D. Garrett 

Mario Garrett, Ph.D., is a professor at the school of social work, San Diego State University.

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