Over recent years, rest has gained increasing importance in relation to health, to the point that the American Heart Association has included sleep as one of the new fundamental pillars for maintaining good cardiovascular health.
How can we achieve quality rest?
It is important to understand the key foundations that must be respected to achieve quality rest. To do so, we must highlight its two main characteristics: sleep duration and sleep quality. Sleep duration refers to the number of hours we sleep, while sleep quality refers to the depth and restorative capacity of that rest.
But what does scientific evidence say about shorter or longer sleep duration—is it healthy?
A group of Japanese and American researchers from the Pittsburgh Sleep Medicine Institute and the Universities of Medicine of Tokyo, Kyoto, and Oita conducted two of the most robust studies to date on sleep duration and health.
The first study, focused on short sleep duration, analyzed data from no fewer than 5,171,710 participants. This study examined associations between sleeping 6 hours or less and mortality, diabetes mellitus, hypertension, cardiovascular disease, coronary disease, and obesity. The results showed that the risk of developing all of the conditions mentioned above increased significantly when participants had such short sleep duration. However, no dose–response relationship was found; simply sleeping less than 6 hours was enough to increase the risk.
Knowing that sleeping too little may be associated with these complications, logic would suggest that sleeping more is better—but is that true?
Let’s look at the second study conducted by this research group, this time focused on long sleep duration. This study evaluated a total of 5,134,036 participants and examined associations between sleeping more than 9 hours per day and mortality, diabetes mellitus, cardiovascular disease, heart attacks, coronary heart disease, and obesity. The results also showed strong associations with these outcomes and, moreover, demonstrated a dose–response relationship: the more excessive the sleep duration, the greater the increase in risk.
So what would be ideal?
Sleeping within the 7–9 hour range recommended by professional associations, in order to avoid the risks associated with both excessive and insufficient sleep.
That said, there are some interesting observations related to sleep. Certain studies highlight that individuals with shorter sleep duration but good sleep quality had greater neural tissue density, as well as greater cognitive persistence and functioning. However, this does not exempt them from the previously mentioned risks.
Regarding sleep quality—the feeling of being rested and energized to face the day—one of the most powerful scientific studies, conducted on 3,340,684 participants across multiple centers in the United Kingdom, emphasized that poor subjective sleep quality significantly increases the risk of coronary heart disease, a major threat to cardiovascular health. However, it did not increase mortality or other outcomes that were associated with sleep duration, as previously discussed.
And what does genetics say?
Finally, it is important to understand that our genetics can significantly influence our sleep. For example, genetically driven insomnia has an estimated heritability of 40%. In addition, both sleep duration and quality may be influenced by genetics, predisposing individuals to shorter or longer sleep, or to better or poorer sleep quality, along with all the associated risks. Understanding genetic risk, as well as factors such as chronotype or circadian rhythm tendencies, can help us significantly improve sleep and overall health.
References
- Lloyd-Jones DM, Allen NB, Anderson CAM, et al. Life’s Essential 8: Updating and Enhancing the American Heart Association’s Construct of Cardiovascular Health: A Presidential Advisory From the American Heart Association. Circulation. 2022;146(5):e18-e43. doi:10.1161/CIR.0000000000001078
- Itani O, Jike M, Watanabe N, Kaneita Y. Short sleep duration and health outcomes: a systematic review, meta-analysis, and meta-regression. Sleep Med. 2017;32:246-256. doi:10.1016/j.sleep.2016.08.006
- Jike M, Itani O, Watanabe N, Buysse DJ, Kaneita Y. Long sleep duration and health outcomes: A systematic review, meta-analysis and meta-regression. Sleep Med Rev. 2018;39:25-36. doi:10.1016/j.smrv.2017.06.011
- Watson NF, Badr MS, Belenky G, et al. Recommended Amount of Sleep for a Healthy Adult: A Joint Consensus Statement of the American Academy of Sleep Medicine and Sleep Research Society. Sleep. 2015;38(6):843-844. doi:10.5665/sleep.4716
- Kwok CS, Kontopantelis E, Kuligowski G, et al. Self-Reported Sleep Duration and Quality and Cardiovascular Disease and Mortality: A Dose-Response Meta-Analysis. J Am Heart Assoc. 2018;7(15):e008552. doi:10.1161/JAHA.118.008552
- Takeuchi H, Taki Y, Nouchi R, et al. Shorter sleep duration and better sleep quality are associated with greater tissue density in the brain. Sci Rep. 2018;8(1):5833. doi:10.1038/s41598-018-24226-0
