You say that "...the level of carbon-14 in a living cell's DNA is directly proportional to the level in the atmosphere at the time it was born, minus a tiny amount lost to radioactive decay" (17 June, p 50). Isn't this only applicable if the cell was made using carbon that had just been absorbed from the atmosphere?
If so, Frisén is actually measuring the time elapsed since the carbon in the DNA left the atmosphere. For vegetarians eating fresh vegetables, the extra time would be quite short, but for meat-eaters the carbon has gone from the atmosphere into plants, which were eaten by animals which in turn lived for some time before being eaten.
Hmm, time for lunch. If I have a salad rather than a steak, will I feel younger?
To continue reading this article, subscribe to receive access to all of newscientist.com, including 20 years of archive content.