We tend to hear we need a "good night's sleep" if we want to be healthy. But there's evidence now that it's not how much you sleep—it's how you sleep. A huge study of more than 88,000 individuals has identified six specific sleep characteristics with the risk of developing 172 separate diseases, and this indicates that poor sleep rhythms can be much more harmful than we ever imagined.Investigators at Peking University and the Army Medical University in China examined data from the UK Biobank, tracking participants for a median of 6.8 years. They didn’t just track how long people slept—they examined six core sleep traits:Sleep lengthSleep onset (bedtime)Sleep rhythm (regularity of sleep-wake cycles)Extent of sleepSleep efficiencyFrequency of night wake-upsTheir findings, published in Health Data Science, show that sleep rhythm—how consistently you go to bed and wake up—was the single strongest predictor of health outcomes.Why Sleep Rhythm Is Important Your Health?Participants with the most irregular sleep rhythms faced up to a 2.8-times higher risk of Parkinson’s disease and a 1.6-times higher risk of type 2 diabetes compared to those with the most regular patterns.Sleep rhythm was associated with nearly half of the 172 diseases identified—three times as many disease links as sleep duration or bedtime alone. That list included hypertension, COPD, acute kidney failure, depression, and several metabolic and cardiovascular conditions.“Time we broaden our definition of good sleep beyond just duration,” says Shengfeng Wang, senior author and epidemiologist at Peking University.Why Bedtime Is More Crucial Than You Might Expect?The research also uncovered significant bedtime-related risks. People who routinely went to bed after 12:30 a.m. were 2.6 times more likely to develop liver cirrhosis than those who went to bed before 11:30 p.m.Meanwhile, low sleep efficiency—time spent actually sleeping versus just lying in bed—was linked to a nearly 1.8-fold increase in respiratory failure risk.Why Wearable Data Changes the Game?This study stands out because it used both self-reported surveys and objective wearable sleep monitor data. And that revealed an important truth: we’re not always accurate about our own sleep. Nearly one in four people who claimed to be “long sleepers” actually slept fewer than six hours a night when measured objectively.This discrepancy matters because previous studies relying solely on self-reported sleep may have underestimated—or overestimated—the role sleep plays in various diseases.The researchers explain, “Some participants with difficulty falling asleep or keeping stable sleep may have spent a long time in bed but have short real sleep.” That misclassification skews results and may mask the impact of poor sleep patterns.Traditionally, public health advice has focused on getting seven to nine hours of sleep per night. But this research indicates that sleep quality, timing, and regularity could be as significant—if not more so—than duration alone. For instance:Consistent sleep rhythms seem to lower risk across neurological, cardiovascular, and metabolic illness.Earlier bedtimes could guard against liver health issues.High sleep efficiency could lower respiratory and cognitive decline risk.Whereas the research can't establish causation—it demonstrates correlations, not cause-and-effect per se—the size of the dataset makes the results difficult to ignore. The researchers also confirmed the findings using a different large database, the U.S. National Health and Nutrition Examination Survey (NHANES), further bolstering the evidence that these sleep characteristics are associated with general health outcomes.If verified by subsequent research, these results may redefine sleep health policy and contribute to guided interventions for vulnerable populations.Disease was once recognized as a consequence of poor sleep, but this study puts a different spin on the discussion. It implies that we may need to consider sleep as much as we consider diet—not merely the "amount" (calories or hours), but the "quality" and "consistency" count as much.As Dr. Wang and collaborators say, the aim should be to "expand our definition of good sleep" to encompass rhythm, timing, and efficiency. At least for the moment, that could entail establishing a regular bedtime, steering clear of late-night screen exposure, and tracking patterns with wearable devices—rather than merely hours slept.