Actually, this is a bit more complicated than it first sounds.
Even most hydrogen atoms found commonly found here on Earth may have at one time been a part of a star, even it they weren't synthesized within the star. Large stars still contain mostly hydrogen and helium with much heavier elements in their core, up to iron. Eventually it goes supernova, producing even heavier elements. But still, most of that hydrogen and helium is just blown off.
But even if those atoms were around before the star was formed, they were at one time part of the star. Does that still not make the atoms "former star stuff"?
It gets more complicated. Let me summarize individual atoms.
Hydrogen:
Hydrogen is pretty abundant on Earth in heavier compounds molecules (e.g., water). Most hydrogen atoms here on Earth were created during big-bang nucleosynthesis. That said, those hydrogen atoms might have very likely been part of a star at some point in the past. A [STRIKE]little[/STRIKE] tiny amount of hydrogen here on Earth comes from [STRIKE]radioactive decay[/STRIKE] cosmic/gamma ray/neutron interactions involving of heavier atoms in the upper atmosphere, but I think that's a negligible amount.
Helium:
Much of the helium created in the universe was created during big-bang nucleosynthesis, although some can also be produced in stars too. But practically
none of that is here on Earth! That's right, nearly all the helium here on Earth
is not star stuff!* Most all the helium here on Earth is the result of radioactive decay (particularly alpha decay) of heavier elements such as thorium and uranium. The rest of the helium left our atmosphere a long time ago. So all the helium that we interact with (helium balloons for example) was formed relatively recently.
*(I say "
not star stuff," but technically it is the decay products of former star stuff.)
Lithium:
the current theory is that most of the lithium (on Earth and in the universe) was created during big-bang nucleosynthesis. The thing about lithium in stars is that it doesn't get produced very much. The nuclear fusion reactions that typically happen in stars skip over lithium for the most part. That's not entirely true, it is possible to produce lithium in certain nuclear reactions, but it is easier to "burn" lithium in nuclear reactions. Stars probably "burn" more lithium than they create, which is why it is thought that most lithium is from big-bang nucleosynthesis.
Beryllium:
Beryllium is weirder yet. Beryllium is another element that gets skipped over in the normal process of fusion in stars. It is believed that most of the stable beryllium in the universe was originally created in the interstellar medium when cosmic rays induced fission in heavier elements found in interstellar gas and dust. So Beryllium is
not star stuff (well, not created within stars anyway).
Boron:
Like beryllium, Boron is also created by by cosmic ray spallation and not by stellar nucleosynthesis. Boron is not created by stars.
Carbon on up:
Now we're talkin' star stuff (or decay products of former star stuff).
[Edit: oh, and
Oral B said:
I never gave it a second thought since obviously humans are created from a sperm and egg, which come from other humans, not stars.
Sperm and eggs are made up of molecules, and those molecules are made of atoms. The atoms in the sperm and egg are still star stuff.* That's what the sources are saying.
*(with the possible/arguable exceptions of the hydrogen atoms, and some of the other lighter atoms if any exist in the cell, that are discussed above.)]
