Maybe unpopular opinion, but after reading Why We Sleep and a dozen articles like this one, I've become increasingly skeptical of sleep research, especially in context of the reproducibility/replication crisis.

There's no dispute there are deleterious effects of sleep deprivation and accruing sleep debt, and that people would be better off with a full 8 hours of sleep. Lack of sleep is harmful for cognition, the cardiovascular, digestive, and endocrine systems, mood regulation, etc. Memory and attention suffering as a consequence after sleep deprivation is undeniable, as we all know. Most of the claims of negative health impact are quantitatively and qualitatively demonstrated to a degree, no debates there.

However, it's the _magnitude_ and severity of the effect, and especially the claims around the mechanics of sleep debt, that warrant skepticism when considering large-sample observations in the real world. Sleep debt supposedly accumulates semi-indefinitely (the research on the "max" limit of sleep debt is lacking), allegedly takes 4+ days to recover per hour of deprivation, and cannot at all be repaid in "lump sums" by for example sleeping in on weekends regularly.

While this may be true to some degree consider someone who averaged 7 hours of sleep on average through high school and college, 6.5 hours in the first 4 years of their career, and 5 hours for the following two years, after getting married and having children before finally reading an article such as this and deciding to eliminate their sleep debt. If it truly accumulated semi-indefinitely, took multiple days per hour of debt, and had a ceiling on "repayment rate", this person (who honestly sounds quite typical and near the median) would either celebrate their 100th birthday, or declare bankruptcy so to speak before becoming debt-free. It's not great science to make these partial claims on the attributes of sleep debt which are incomplete.

Further, if you read Why We Sleep, the logical conclusion (from the case effectively being made) if sleep debt were really as bad as claimed would entail that the 40% of the population in modern society would have hardened arteries, moderate to severe hormonal and mood dysregulation and other significant mental and physical issues by middle-age. Yet we don't observe this in anywhere near 40% of the population; not even in the majority of those individuals averaging 5 hours of sleep or less nightly.

Conditions like severe obstructive sleep apnea, defined as 30+ hypoxic events per hour, are certainly correlated with hypertension and heart issues. But sufferers should be hardly functioning, cognitively or physiologically, were sleep deprivation to be as harmful as advertised* and you'd wonder how anyone with the condition could get a diploma or maintain a job according to the sleep researchers. Many OSA sufferers can literally go without a single sustained hour of sleep, ever, over the majority if not the entirety of their lives. It's true there's a higher incidence of cardiovascular issues in this population, but the condition is also comorbid with obesity, which has a greater impact on cardiovascular health.

And finally, the majority of studies and meta-analyses finding increases in general mortality rate amongst people who sleep under 7 hours a night, also produce the same finding amongst people averaging over 9 hours a night.

*The one claim which is well-supported and cannot be disputed is that sleep debt does result in significant sleepiness and delayed reaction time, as we sadly see on a yearly basis in many countries that practice daylight savings, with a spike in fatalities and severe bodily harm from car crashes like clockwork the Monday the clocks are shifted forward.

**Also, there is another claim that is true - prolonged, absolute sleep deprivation results in fairly rapid total system failure and inevitable death, much more quickly than the majority of chronic diseases, including heart, kidney, or lung disease (which people can live with for years or decades). It's on par with the most aggressive forms of cancer. Please don't mistake this post as stating sleep deprivation/debt is "not a big deal", it certainly is. However the science does not, in my opinion, appear to be nearly as robust, and has many more exaggerated claims than other areas of physiological/health research.