“Sleep is that golden chain that ties health and our bodies together.”
- Thomas Dekker, 16th century playwright“Sleep is a biological necessity, and insufficient sleep and untreated sleep disorders are detrimental for health, well-being, and public safety.”
Getting a good night’s sleep is foundational for our health. However, as with other foundational recommendations, it comes with a few often ignored or unknown caveats. Just as there are the early-to-rise “Mourning Doves” and late-to-rise “Night Owls,” countries show significant differences in their aggregate sleep. Japan anchors the Mourning Doves France the Night Owls; the difference is a bit over 1.5 hours.
It is unclear why this is the case; scientists have considered underlying biological and cultural differences. Latitude has been found to correlate with sleep; those living further from the equator generally sleep longer. Globally, sleep duration and health are believed to have a strong relationship. However, if that is the case,
“Then countries with shorter sleep duration would be expected to have worse health outcomes while controlling for other relevant variables.”
A new study in PNAS attempts to shed some light on sleep and health. The researchers began by considering average national sleep durations with health conditions for 71 countries. For each country, as we would anticipate, better health correlated with a nutritious diet and greater wealth, as measured by GDP. However, no significant correlation existed between sleep duration and heart disease, diabetes, or life expectancy. The only significant correlation was that countries with longer sleep durations had more obesity.
What National Averages Get Wrong About Sleep and Health
Before we party hearty and let our freak flag fly into the late night over their conclusions, let’s talk about a classic research trap: the ecological fallacy. Here’s the gist: just because something is true at the group level doesn’t mean it’s true for individuals within that group. These country-level aggregates can hide huge differences. Japan has its share of night owls, and France has its share of mourning doves. While the research findings are clear, they are incomplete. To address the ecological fallacy, the researchers turned to self-reported, individual-level data on sleep duration and health based on a global survey of 5000 participants across 20 countries [1]
- While “optimum” sleep duration varied from country to country, an individual’s view of the ideal amount of sleep was strongly correlated, “suggesting that average sleep durations tend to conform with local cultural norms.”
- Unlike the country-level aggregates, for individuals, longer sleep was associated with self-reported better mental health, lower depression, fewer chronic health conditions, and better subjective health.
- However, for individuals believing sleep improves health, getting a “last night’s sleep” more distant from the cultural average was linked to worse self-reported health outcomes! Why might that be?
As with many biological effects, up to a point, health improved with more sleep, after which it declined; the Nike swoosh of a
nonlinear relationship. Sleep has a “Goldilocks” range, not too little nor too much. However, sleeping in sync with our cultural expectations benefits our well-being; whether there is some placebo effect or these expectations reflect the wisdom of the crowd remains unknown. Finally, as the media often reports, the research found we do not get enough sleep – the sweet spot for optimal sleep and health was higher than each country’s average sleep time, suggesting most people sleep less than what’s ideal.
Aggregate sleep averages do not predict health, nor is there an “ideal” amount of sleep. But culture plays a significant role, and this finding leads us to consider cultural consonance.
Sleeping Like Everyone Else Might Be Good for You
Cultural consonance bridges the gap between the shared knowledge of a society and the individual’s lived experience. It refers to the extent to which a person’s beliefs and behaviors align with the collectively held cultural models of how life should be lived, offering a measurable and biologically meaningful link between culture and health. In this instance, the difference between the culturally appropriate amount of sleep and the actual sleep we get.
When individuals can approximate these cultural ideals in their daily lives, they tend to enjoy better health outcomes. For instance, in a Brazilian study, individuals with higher cultural consonance in lifestyle and social support had significantly lower systolic blood pressure than those with low consonance, even when controlling for factors like age, sex, BMI, and socioeconomic status. Other factors, besides consonance or dissonance, can be at play. For example, night shift workers experience an alien infrastructure geared more toward daytime activity and generally have poorer health. Genetics also plays a role.
"Despite the common advice to get eight hours of sleep, our findings suggest that sleep recommendations need to be adjusted based on cultural norms. There is no one-size-fits-all amount of sleep that works for everyone."
- Dr. Steven Heine, Professor of Social and Cultural Psychology, University of British Columbia
There is no magic number when it comes to sleep—only a Goldilocks zone shaped by biology and culture. Sleep duration is best understood not as a standalone metric but as part of a broader story involving expectations, identity, and lifestyle. In the end, it’s not about hitting eight hours; it's about finding your personal, biological sweet spot and, to some degree, aligning with your cultural rhythm.
[1] The survey characterized sleep as “typical” and “last night’s,” with the latter being a better predictor of health.
Source: Healthy Sleep Durations Appear To Vary Across Cultures PNAS DOI: 10.1073/pnas.241926912
Chuck Dinerstein, MD, MBA
Director of Medicine
Dr. Charles Dinerstein, M.D., MBA, FACS is Director of Medicine at the American Council on Science and Health. He has over 25 years of experience as a vascular surgeon.
