“Sleep regularity is…a stronger predictor of all-cause mortality than sleep duration.”
The Snapshot: Sleep advice usually starts with duration. The strongest evidence-based starting point is often regularity—keeping sleep/wake timing consistent—because day-to-day variability is linked to meaningful health outcomes and may predict risk beyond duration in objective data. (Sletten et al., 2023; Windred et al., 2024)
The Featured Resource
National Sleep Foundation: Sleep Time Duration Recommendations
Definitions you can actually use
Sleep duration: Total time asleep (not just time in bed). (Watson et al., 2015)
Sleep regularity: Day-to-day consistency in sleep timing (bed/wake). (Sletten et al., 2023; Windred et al., 2024)
Sleep efficiency: Percent of time in bed spent asleep (commonly used clinically). (Edinger et al., 2021)
The Research:
What the Evidence Actually Supports
Sleep regularity (Tier 1–2)
A National Sleep Foundation consensus statement concludes that consistency of sleep onset and offset timing is important for health, safety, and performance. (Sletten et al., 2023).
In a large prospective cohort with objective sleep measures, sleep regularity predicted all-cause mortality more strongly than sleep duration in equivalent statistical models. (Windred et al., 2024)
Verdict: Treat regularity as a first-line target—not just a “nice to have.”
Sleep duration (Tier 1–2)
Adult consensus recommends ≥7 hours per night on a regular basis to promote health. (Watson et al., 2015)
NSF consensus ranges provide age-based “appropriate” bands (e.g., adults generally 7–9 hours). (Hirshkowitz et al., 2015)
Verdict: Duration matters—especially avoiding chronic short sleep—but “optimal” isn’t one number for everyone.
Why timing matters (the Two-Process model) (Tier 2)
The two-process model explains sleep as an interaction between a homeostatic sleep drive (pressure builds with time awake) and circadian timing (your internal clock). (Borbély, 2016; Borbély, 2022)
Borbély, 2016/2022 overview of the model
❝Verdict: If your schedule is erratic, you can “have time in bed” and still miss quality sleep because your clock and sleep drive are misaligned.
(Borbély, 2016)
Sex differences in “optimal” sleep duration
The Question: Do women need more sleep than men?
What the evidence supports: Women average slightly longer sleep in population data and report more insomnia/sleep disturbance, but adult duration recommendations are not sex-specific. (Watson et al., 2015; Burgard & Ailshire, 2013; Nowakowski et al., 2013)
Claim | Evidence Tier | Verdict | What to do |
|---|---|---|---|
Adult sleep-duration recommendations differ by sex | Tier 2 (consensus) | Not supported. Same baseline target (≥7h) for adults. (Watson et al., 2015) | Use ≥7h as baseline; personalize based on symptoms/function. (Watson et al., 2015) |
Women sleep more than men on average | Tier 2 (national diary data) | Supported (small effect).(Burgard & Ailshire, 2013) | Treat as a population average, not a rule. (Burgard & Ailshire, 2013) |
Women “need more” sleep biologically (as a general rule) | Tier 3 (interpretive) | Overstated. Higher insomnia risk ≠ universal more-hours requirement. (Nowakowski et al., 2013) | Focus on regularity + insomnia treatment when indicated. (Edinger et al., 2021; Nowakowski et al., 2013) |
“Optimal duration” differs by sex | Tier 2 (observational, outcome-specific) | Sometimes small/model-dependent. (Ungvari et al., 2025) | Don’t convert outcome curves into universal rules. (Ungvari et al., 2025) |
The Red Flags
How to spot sleep BS
These patterns signal low-quality sleep claims (and map onto the same manipulation patterns you’ve used in prior issues):
One weird hack beats physiology (sleep is regulated by homeostatic + circadian processes). (Borbély, 2016)
Screens don’t matter (they can delay timing/suppress melatonin). (Chang et al., 2015)
Caffeine “doesn’t affect me” (people often underestimate effects; objective disruption exists). (Drake et al., 2013)
The Framework:
The “Circadian Anchor” plan (what to do first)
This is the simplest implementation of the strongest levers: regularity → light timing → caffeine timing → duration floor. (Sletten et al., 2023; Gooley et al., 2011; Drake et al., 2013; Watson et al., 2015)
Step 1 Anchor wake time (most days) | Step 2 Protect light timing (evening) | Step 3 Move caffeine earlier than you think | Step 4 Hit the duration floor |
|---|---|---|---|
Set a wake time you can hit most days (including weekends as much as feasible). Regularity is the lever with the strongest “signal” across the literature. | Even normal room light before bed can suppress melatonin and shift internal timing; bright screens can do the same. | A controlled study found caffeine can meaningfully reduce sleep even when taken 6 hours before bedtime. | Use ≥7 hours as the adult floor target; if you can’t reach it yet, prioritize consistency first, then gradually extend opportunity for sleep. |
If sleep is chronically bad: what’s actually evidence-based?
For chronic insomnia disorder, an AASM clinical practice guideline recommends behavioral/psychological treatments (CBT-I components such as stimulus control and sleep restriction therapy are supported). (Edinger et al., 2021)
Verdict: If you’ve had persistent insomnia symptoms, don’t “biohack harder”—use validated treatment pathways. (Edinger et al., 2021)
Verify This
Sleep regularity and mortality: Windred et al., 2024 (SLEEP)
Sleep regularity consensus: Sletten et al., 2023 (Sleep Health)
Adult sleep duration ≥7h consensus: Watson et al., 2015 (SLEEP/PMC)
NSF duration bands: Hirshkowitz et al., 2015
Light and melatonin: Gooley et al., 2011
Screens and circadian delay: Chang et al., 2015
Caffeine timing: Drake et al., 2013
Insomnia treatment guideline: Edinger et al., 2021
Coming Next Week
Week 7: Flexibility
This series will continue to move through Physical Wellness, as we make our way through all of the dimensions of wellness. Next week we will cover the topic of flexibility, what stretching can change (and what it can’t), and how to stop chasing “mobility hacks” that don’t generalize.
Editor's Note
Sleep is one of the easiest topics for wellness content to overpromise: one supplement, one tracker, one trick.
The actual science keeps pointing back to fundamentals: regularity, timing inputs (light/caffeine), duration floor, and evidence-based treatment when sleep is persistently impaired.
—Brian
About the author: Brian S. Dye, Ed.D., is the founder of Applied Wellness, an evidence-based wellness education platform focused on helping people cut through wellness noise and apply credible guidance in real life. Learn more →
References
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Borbély, A. (2022). The two-process model of sleep regulation: Beginnings and outlook. Journal of Sleep Research, 31(4), e13598. https://doi.org/10.1111/jsr.13598
Burgard, S. A., & Ailshire, J. A. (2013). Gender and time for sleep among U.S. adults. American Sociological Review, 78(1), 51–69. https://doi.org/10.1177/0003122412472048
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