The Relationship Between Sleep Duration and Longevity

Sleep is an important aspect of overall health and wellness. While this is typically well known, according to the National Sleep Foundation, over 35% of all US adults report sleeping less than seven hours per night. [1] How much and how well you sleep impacts metabolism, energy levels, mood, and immune health. And sleeping poorly has well-established connections to depression, type 2 diabetes, obesity, and cardiovascular disease (CVD). [2,3] So it’s no surprise that research also shows that optimal sleep duration and sleep quality are associated with lifespan and longevity. This article unpacks the scientific evidence behind the associations between sleep and longevity and dives into the factors that may positively or negatively affect that relationship.



What is the optimal sleep duration for longevity? 

Many large meta-analyses (pooled-analysis of multiple studies) investigate the impact of sleep duration and sleep quality on all-cause mortality. All-cause mortality is defined as the death rate from all causes of death for a population in a specified time period. This outcome is often measured in large cohort studies to determine how specific inputs (like sleep duration) impact health at a population level. Because longevity is defined as the duration of one’s life, the risk of death from all causes is a common way to generate hypotheses on factors that can improve longevity. 

Researchers of a meta-analysis of 16 prospective cohort studies with a combined 1.3 million participants investigated the impact of sleep duration on all-cause mortality. [4] This study found that short sleep duration (defined here as less than six hours per day) was associated with a 12% greater risk of death than those who sleep between six and nine hours. Interestingly, this study also showed that long sleep duration (greater than nine hours a day) was also associated with a 30% greater risk of death than their 6-9 hour sleeping counterparts.

A meta-regression of 40 prospective cohort studies with over 2.2 million total participants found that sleeping less than seven hours a day was associated with an increased risk of all-cause mortality. [5] Compared to sleeping for seven hours a day, the following average sleep durations were significantly associated with an increased risk of all-cause mortality: [5]

• 4 hours: 5% increased risk 
• 5 hours: 6% increased risk
• 6 hours: 4% increased risk
• 7 hours: (Reference group) 
• 8 hours: 3% increased risk
• 9 hours: 13% increased risk
• 10 hours: 25% increased risk 

Similarly, a meta-analysis including 67 studies of over 3.5 million participants found that both short and long sleep was associated with an increased risk of all-cause mortality and CVD. [6]

Based on these large meta-analyses, the optimal sleep duration for healthy adults appears to be 7-9 hours per night, an optimal range that the Sleep Foundation also recommends. [7]*

*The Sleep Foundation comprises 18 experts who review and synthesize hundreds of validated studies related to sleep. 



Are there dangers associated with too much sleep? 

You may have noticed from the list above that more isn’t always better—and the research is consistent with this finding.   

Studies show that there is either a U-shaped or a J-shaped curve between hours slept and risk for all-cause mortality—clearly indicating that there’s a sweet spot for how long you should sleep for health and longevity. [8]

One study found that a sleep duration of 10+ hours was associated with a 34% increased risk of all-cause mortality in men and a 48% increased risk of all-cause mortality in women compared to those who sleep an average of seven hours a day. [8]

So, why is sleeping longer not always better for health? Researchers hypothesize that prolonged sleep duration may sacrifice sleep quality. When sleeping for 10 or more hours a night, the body may not be getting quality, restful sleep. Low-quality sleep may leave you feeling tired throughout the day, waking up during the night, and spending more time trying to fall asleep. Quality sleep is crucial for the body’s repair processes necessary for longevity-promoting effects. [9]

Confounding factors in the relationship between sleep duration and longevity 

As with any scientific topic, there are additional—or confounding—factors that can contribute to the relationship observed between sleep duration and longevity. Here are a few examples. 

Biological sex

One study found that men had higher risks of CVD mortality than women with sleep durations less than 5 hours or 10+ hours. On the other hand, women were at a significantly increased risk of CVD mortality with sleep durations of eight and 9 hours, indicating that women, unlike men, may have a dose-dependent risk increase for sleep durations that exceed 7 hours of sleep. [8]

Another study showed that there might be sex differences in risk of death based on sleep duration between men and women. The risk of death was not statistically significant in men, although prolonged sleep maintained statistical significance. This result differed compared to women, where women were at an increased risk of death at both short and long sleep duration. [5]

Chronological age

Participants’ age proved to statistically significantly modify the association between sleep duration and mortality risk in multiple studies. In a study of nearly 145,000 men, age significantly modified the relationship between sleep and all-cause, cancer, and other-cause mortality. The study showed that younger but not older men who, on average, sleep for less than 7 hours per 24-hours had a significantly increased risk of all-cause mortality compared to their older male counterparts. [8]

Being physically active strengthens the relationship between sleep and longevity?

Some lifestyle factors may strengthen the relationship between sleep and longevity—meaning study participants who had an optimal sleep duration and had certain additional factors were less likely to die from all causes.  

The relationship between sleep and longevity was strengthened based on self-reported physical activity. Participants with a low physical activity level showed a strengthened death risk reduction compared to those who are moderately and very physically active. [10] This finding may seem counterintuitive, as being physically active is a well-established longevity-promoting lifestyle factor. Therefore, researchers hypothesize that perhaps getting regular quality sleep may potentially counteract the impact of low physical activity on longevity. However, further research is certainly needed to unravel this hypothesis. 

Why InsideTracker?

Based on up-to-date research, the consensus is that optimal sleep duration and quality can influence longevity. Based on multiple meta-analyses of large cohort studies, the optimal sleep duration for healthy adults is 7-9 hours per night. Sleeping fewer than seven hours and greater than nine hours per night was associated with an increased risk of all-cause mortality in several studies. All of this being said, prioritizing sleep quality is easier said than done. 

Here’s how InsideTracker approaches optimizing sleep. The InsideTracker sleep goal tracks and analyzes the blood biomarkers associated with sleep including vitamin D, magnesium, and cortisol. If a sleep-related biomarker is unoptimized on your most recent blood test, you’ll receive science-backed recommendations to improve that biomarker level, which can then improve your sleep. The relationship between sleep and biomarkers is reciprocal—meaning improving sleep quality can also improve blood biomarker levels and improving those biomarker levels may also improve your sleep quality. 



InsideTracker customers can connect their fitness trackers (currently, Oura Ring, Garmin, Fitbit, and Apple Watch) to the InsideTracker mobile app. Customers who integrate their fitness tracker can unlock deeper, more meaningful insights into their health. The app tracks and analyzes the trends in your sleep—because we know that bad nights of sleep happen. Analyzing trends over time can help you understand and take action. 

Be sure to turn your push notifications on to receive InsideTracker ProTips, nuggets of evidence-based recommendations that are actionable based on your recent data. For example, your sleep duration may indicate that you need to alter caffeine intake, or your deep sleep may demonstrate the benefits of a supplement. Connecting your fitness tracker to InsideTracker can help you make sense of your data and take action. Want to refer back to a previous ProTip? You can view your previous InsideTracker ProTips in the notification center.

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References

[1] ps://www.sleepfoundation.org/how-sleep-works/sleep-facts-statistics  [2] https://pubmed.ncbi.nlm.nih.gov/26118561/ [3] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5605599/ [4] https://pubmed.ncbi.nlm.nih.gov/20469800/  [5] https://pubmed.ncbi.nlm.nih.gov/27067616/ [6] https://pubmed.ncbi.nlm.nih.gov/28889101/   [7] https://www.sleepfoundation.org/how-sleep-works/how-much-sleep-do-we-really-need  [8] https://pubmed.ncbi.nlm.nih.gov/34477853/  [9] https://pubmed.ncbi.nlm.nih.gov/25009494/ [10] https://pubmed.ncbi.nlm.nih.gov/34237797/