You might think getting 8 hours of sleep is all that matters. But the time you go to bed can make or break how rested you feel in the morning.

Your Body Runs on a Rhythm

Your body follows an internal clock called your circadian rhythm. This 24-hour cycle controls when certain hormones rise and fall, including the ones that tell you when to sleep and wake up.

One of those hormones is cortisol. Cortisol gets a bad reputation as a stress hormone, but in healthy amounts, it plays a key role in your daily rhythm. It naturally rises in the morning to help you wake up and drops at night to help you rest. This pattern is known as your daily cortisol curve.

How Staying Up Late Affects Sleep Quality

Cortisol’s natural drop in the evening helps your body prepare for sleep. But when you stay up late, you push past this natural wind-down, and that can throw off your whole rhythm.

It also affects your deep sleep, the stage of sleep that helps your body repair and recover. Deep sleep mostly happens in the first few hours after you fall asleep. Your body is set up to start that deep sleep earlier in the night. So when you delay bedtime, your body doesn’t fully shift the deep sleep window to match. Instead, you might miss out on part of it. The result? Less repair, less recovery, and more grogginess in the morning.

If you want to understand more about how your cortisol rhythm affects your energy throughout the day, check out our article: “The Secret to Regaining Your Energy? Reset Your Daily Cortisol Curve.”

How to Support Better Sleep Timing

• Aim for a consistent bedtime. Going to bed and waking up at the same time helps regulate your rhythm.
• Dim the lights in the evening. This signals to your brain that it’s time to wind down.
• Avoid caffeine at least 6 hours before bed. Caffeine too late in the day can keep you from falling asleep.
• Get bright light exposure in the morning. Natural light within 30 minutes of waking helps set your body clock for the day.

Bottom Line

It’s not just how much you sleep, it’s also when. Going to bed in sync with your body’s natural rhythm helps you get more deep, restorative sleep so you can wake up feeling truly refreshed.