~ Young At Heart

NY Post, 06-21-06

THINK you've got the body of someone half your age? Turns out you're right. If you're in your late 30s, your muscles are only around 15 years old, say scientists. And some of your parts aren't much older than a newborn's - your eyelashes are only 2 months old, while the surface of your skin has been around a mere two weeks.

That's the word from scientists in Sweden uncovering new information about the way the body breaks down and renews itself. They found that as you get older, your cells are constantly dying off and being regenerated, meaning many parts of your body are years younger than your chronological age.

Your tastebuds? New every 10 days. Your bones? Ten years old, on average.

Your cerebellum? It's roughly three years younger than you are, which is something to consider next time you're tempted to shave a few years off the age in your online dating profile.

Scientists have long wondered about these matters, but answers have been hard to come by. The breakthrough of Swedish neurologist Jonas Frisen, as reported in this month's New Scientist magazine, was figuring out how to use carbon-14 dating - used to measure the approximate age of archeological finds - to precisely gauge the age of body cells.

To pull this off he had an unlikely ally: the Cold War. The technique measures the amount of carbon-14, a radioactive isotope, in a sample of organic matter. That level decays steadily over time, so the amount that remains determines how old it is - but only within a 30- to 100-year margin of error.

What enabled Frisen to improve his accuracy was the fact that at the peak of Cold War nuclear testing, there was double the usual amount of this isotope in the atmosphere - a "bomb spike" that started declining when a partial test ban treaty took effect in 1963. Comparing the level of carbon-14 in a cell to the level in the atmosphere when Cold War testing was at its peak allowed Frisen to determine the age of various body parts.

The cells that work the hardest have the shortest life spans, he and his team found. Red blood cells, for example, last only 120 days. The lining of your gut renews itself the quickest, with the cells regenerating every five days. (Your actual guts are older - close to 16 years, or slightly older on average than your muscles.)

Ultimately the researchers hope to figure out if and how brain cells regenerate. Studies are also being done to learn more about heart, liver, eye and fat cells.

Such work could help with treatments for a number of diseases, including Parkinson's, Alzheimer's, heart disease, depression - even obesity. (Scientists don't know if obese people have more fat cells, or just fatter ones.)

Parkinson's may be related to cells not being created adequately to replace the ones that die. As for depression, a Columbia neurologist, Rene Hen, demonstrated that mice became depressed if the stem cells in a particular region of the brain weren't making enough new neurons. (Prozac works in part by stimulating their growth.)

There are still a lot of questions researchers hope to answer. For example, does all of your body eventually get renewed?

How many bodies do you go through over the course of your life?

By the end of your life is any of the body you were born with still left?

And lastly, if you really have the body of a teenager, how come you're not getting more dates?

Of course the research is likely to generate other questions among readers - like, for example, why don't I have the ripple-free skin of an eight-year-old?

For the record, the answer is that your mitochondrial DNA ages at the same rate you do. If scientists ever figure out a way to slow its aging down, or repair it, they might be able to delay the effects of aging.

Until then, there's always Botox.

chris.erikson@nypost.com


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