You upgraded your mattress. Track your sleep score religiously. Clock a solid eight hours of shuteye a night. But you may be overlooking one of the most important sleep metrics of all: when you actually go to bed and wake up.
Sure, the number of hours you get matters. But even if you’re in the seven-to-nine hour sweet spot, constantly shifting when you snooze means you’re not crushing your ZZZ’s quite as hard as you think.
Why sleep consistency matters
Keeping consistent sleep and wake times may be just as important as getting enough sleep—and perhaps even more so, says Eric Zhou, PhD, a sleep medicine clinician-researcher and associate professor at Harvard Medical School.
Your body thrives when it knows what time it is. “The body runs on a circadian clock that helps regulate blood pressure, glucose metabolism, hormone release, and even autonomic nervous system activity,” says M. Taruj Ali, MD, a board-certified sleep and obesity medicine physician and medical director of sleep medicine at Mary Washington Healthcare. “When sleep and wake times keep shifting, those systems are repeatedly being asked to operate at the wrong biological time.” The fallout can extend well beyond feeling tired. Keep throwing that clock off, Dr. Ali says, and the effects can ripple throughout the body. Think more inflammation and worse cardiometabolic health.
There’s a name for this circadian whiplash: social jet lag, which could leave you feeling as though you’ve stepped off a cross-country flight without even leaving your bedroom. “Even though you may have slept for hours and hours, you still feel ragged and disoriented when you wake up. That’s because the change in timing throws your body into a spin cycle,” says Zhou. Need proof your body hates a schedule change? Consider the curveball of moving your clock an hour forward each spring. Studies have linked the change to a temporary uptick in heart attacks and hospital admission in the days after. And that’s just a one-hour shift once a year—not a nightly occurrence.
What the research shows
Feeling groggy is one consequence of keeping your sleep schedule out of whack. But that might be the least of your worries.
In a 2024 study of over 60,000 adults in the UK, higher sleep regularity was associated with as much of a 48% lower risk of all-cause mortality, a 39% lower risk of cancer mortality, and a 57% lower risk of cardiometabolic mortality. But that’s not all. A 2025 review of 59 studies linked sleep-timing irregularity with a higher risk of depression and anxiety, elevated body-mass index (BMI), insulin resistance, hypertension, and cardiovascular events—plus a 26 to 53% increase in dementia risk. Another large UK study found that irregular sleep was associated with a higher risk of developing type-2 diabetes—even in those who slept seven-plus hours a night. On a brighter note, a 2025 study from Japan found that higher sleep regularity was associated with higher cognitive function and higher levels of brain-derived neurotrophic factor (BDNF), a protective protein that supports neuroplasticity and mental health.
Most of these studies are observational, so none of this ensures that a consistent sleep schedule is a cheat code for dodging disease (or death). “Still, the signal is remarkably consistent, and the evidence is strong enough that consistency should be considered one of the basic pillars of healthy sleep,” says Dr. Ali.
How to make your sleep schedule more consistent
For some, it’s easy to keep regular sleep-wake times. But for others—say, night owls, insomniacs, or those without a 9-to-5—sticking to a schedule is easier said than done.
