A 2007 study published in the journal Archives of Internal Medicine, found that a habitual midday nap was associated with a reduction of over 30% in mortality caused by cardiovascular problems.

The reasons for the study's findings are currently unclear - and research is ongoing.

Epidemiological studies on the relations between cardiovascular health and siesta have led to conflicting conclusions, possibly because of poor control of confounding variables, such as physical activity. It is possible that people who take a siesta have different physical activity habits, for example, waking earlier and scheduling more activity during the morning."

Source :Wikipedia

Note : Since 2007, several other studies have investigated other possible benefits of a daytime nap. See the study below regarding improved cognitive performance. (Again, the reasons for the apparent benefits are not clear.)

Despite the fact that our meta-analyses included almost exclusively laboratory studies, daytime napping in the afternoon improved cognitive performance with beneficial effects of early nap. More studies in real work condition are warranted before implementing daytime napping at work as a preventive measure to improve work efficiency."

Source :Effects of a Short Daytime Nap on the Cognitive Performance: A Systematic Review and Meta-Analysis Int J Environ Res Public Health, v.18(19); 2021 Oct PMC8507757