Perhaps I should be more intellectually vigilant but this claim strikes me as so likely to be true that I wouldn’t bother trying to find a citation for it.
I didn’t make it into anything and I don’t take it as axiomatic, I just wouldn’t spend time looking it up. It also sounds true to me based on my knowledge of biology, upon which I get to draw inferences I think are reasonable.
In my experience, the people who are frequently sleep deprived for a few years don't seem to be worse for it afterward.
My main sources of anecdote for this are grad school students with hectic school and advisor setups (who often are partly sleep deprived for much of 3+ years), and parents who have several children in short succession (ensuring their sleep is ruined for roughly 2 years).
In neither case do those groups seem to suffer significant long-term effects that are obviously from the sleep deprivation.
