Why You're Still Tired After 8 Hours of Sleep (How to Fix it)

I did everything right. I went to bed at the same time every night. My room was cold. My phone was in another room. I wasn’t eating late. I was getting a full eight hours.

And my Oura ring kept scoring me in the 70s.

The kind of score that makes you stare at your phone at 6am while your tea steeps and think, well, I guess this is just my life now.

I spent a few months like that. Sleeping enough hours but never waking up feeling like sleep had done its job. If sleep were an employee, I would have started documenting performance issues.

So I started digging.

Your body has to get cold to fall into deep sleep. Your actual core body temperature needs to drop about 1 to 1.5 degrees for your brain to shift into slow-wave sleep, which is the stage where your body does its real repair work. Cellular cleanup and muscle recovery. The stuff you assumed was happening while you slept but wasn’t.

The way your body pulls this off is surprisingly mechanical. Blood vessels in your hands and feet dilate, warm blood rushes to your extremities, and your core cools down. Your brain reads that temperature drop as the green light to go deep.

When that cooling process stalls, you stay in lighter sleep stages. All night. You can clock eight full hours, and your body barely touches the sleep that matters. It’s like sitting in a parked car for three hours and calling it a road trip.

For women in midlife, this gets worse. Estrogen plays a role in thermoregulation, and as levels shift during perimenopause, your body’s internal thermostat gets less precise. You don’t have to be having hot flashes for this to affect you. The disruption can be subtle enough that you’d never connect it to sleep quality. You just know you’re tired.

Glycine is the simplest amino acid your body makes. But production can fall short, especially under stress or when your diet isn’t covering the gap. When you take it before bed, it crosses the blood-brain barrier and acts on NMDA receptors in your brain’s master clock, the suprachiasmatic nucleus. (I know. The name sounds like a dinosaur. Stay with me.) Those receptors trigger vasodilation, which is the fancy way of saying your blood vessels open up and heat moves out of your core. The exact sequence your body needs to enter deep sleep.

In clinical trials, 3 grams of glycine before bed improved both how quickly people fell asleep and how much time they spent in restorative sleep stages. It also reduced daytime fatigue the next day. The primary researchers worked for a company that manufactures glycine, which I want to be transparent about. But the mechanism has been independently validated through research at Stanford’s sleep lab, and the safety data is solid.

How to take it: 3 grams, about 30 to 60 minutes before bed. I’ve taken it two hours before bed and it worked just as well. It’s cheap and tastes slightly sweet. Dissolves in water, but I take it with a little bit of strawberry kefir for a probiotic boost.

Since I started taking it, my Oura scores went from the 70s to the mid-90s. I wake up feeling like a new woman.

Who it’s for: Women who are doing the sleep hygiene basics and still not getting restorative sleep. If your body isn’t cooling down properly at night, glycine gives it the nudge it needs.

Who should skip it: Anyone on clozapine, anyone with kidney or liver disease, and anyone who is pregnant or breastfeeding. If you’re on blood sugar medication, talk to your doctor first, because glycine can affect glucose levels. You should always talk to your doctor before taking new supplements, of course.

I spent years thinking I was just a bad sleeper. Turns out my body had forgotten one step. It needed to get cold, and it couldn’t do it on its own anymore. Three grams of a boring little amino acid fixed that.