On a gorgeous Spring day, I awoke to find birds singing and the sun shining. After rolling up a window shade and brewing a fresh pot of coffee, I was ready to tackle overnight emails and visit the great Twitter machine.
The first thing I saw?
("Your atoms?" Do I own my atoms? Does anyone? And doesn't that figure seem, well, a little high?)
OK, wait, I'm a scientist, so it's just in my nature to be skeptical. But with 50+ re-tweets, and 18 'favorites' already, I felt this 'fact' needed a bit of perspective. Surely a little digging (assisted by @doctorchemed and @Chemjobber, thanks!) will turn up the truth, right?
First, let's stop at the likely source for the factoid: this segment from a 2007 All Things Considered episode. It mentions the mysterious "98%" figure, and goes on to give a perfectly rational-sounding explanation, backed up by a scientist (Ph.D. = credibility). The reporters' comments tend towards the usual suspects - oxidative stress, dead skin cells, DNA copying errors. It's well known that several body tissues do indeed cycle through, so they leave another breadcrumb trail for us to follow: "...a study published in the Annual Report for Smithsonian Institution (huh?) in 1953..."
|"Mr. Isotope" Seal of Approval?|
Make sense yet? It's a funding appeal! The speech recounts the glory of the atomic age, from the Curies to the end of WWII, and the line about the "approximately 98 percent of the atoms in us..." (p. 232) serves as another brick in the staircase, built towards the temple of program renewal."We need more people trained in the use of isotopes — people who can apply this new tool to tomorrow's problems in medicine, science, and technology - more 'isotopologists'...We have hardly scratched the possibilities of scientific achievement."
Since Aebersold discloses no study or reference data, my skepticism mounts. If we really recycle almost our whole body, how could we detect blood contaminants, such as PFOA or BPA? How could teeth be stained, if you were always churning out new enamel? (you're not) How would "belly-button microflora" from different places still be detectable on you, if you were always throwing them away?
|George de Hevesy|
Source: Nobel Foundation
So, why all this focus on bones, bones, bones? Turns out, the skeleton in an average human being weighs somewhere around 12-18% of total weight. If 20% is renewed, that means 80% is not. Thus, without considering any other vital body system (neurons? scar tissue? cartilage?) the 98% exchange can't be correct - somewhere around 10% of your body's atoms stay unchanged every year!
(Readers, if you see factual or logical errors here, I welcome future impassioned discussions in the comments!)