I mention in our masterclass about Greek population study.
"A case-control studyTrusted Source of a Greek population found that those who took a nap were at a lower risk of developing coronary heart disease than those who did not. The study appeared in 1988, and it set the tone for much of the ensuing research on napping. Later, a large cohort study, also of a Greek population, confirmed the findings. It suggested that those who napped regularly had a 37% lower riskTrusted Source of death from coronary heart disease than those who did not nap."