Part of the Longevity Metrics Series: Auditing My Health as I Turn 55

My 55th birthday is June 19th. And as it approaches, I've been doing something I've been doing for decades before I take my next turn around the sun: auditing myself. This year I'm looking  at ten health metrics predictive of longevity, one by one. Then I want to use the next year to move the needle on the ones that need it.

Last week was grip strength. This week: sleep.

I chose sleep second because every other metric I'll examine over the coming month is directly affected by how well you sleep. It made no sense to discuss any of them without establishing this foundation first.

Why Sleep Quality Matters More Than Sleep Duration

We've spent a decade being told that eight hours is the goal. Get eight hours. Protect your eight hours. And yes, total sleep time matters. But what the research increasingly shows is that it's not just how long you sleep but what your brain is actually doing while you're there.

Sleep is not a passive state. It's one of the most metabolically active and neurologically complex things your body does. And the quality of that activity, measured by how much time you spend in specific sleep stages, determines outcomes that show up everywhere else in your health data.

My Oura ring scores typically sit in the high 70s to low 80s. For context, Oura considers 85 and above optimal, and 70 to 84 good. I'm consistently in the solid range. But when I look beyond the headline score at what's actually happening inside those roughly seven hours, the picture gets more interesting.

What Deep Sleep Does (And Why You're Probably Not Getting Enough)

Deep sleep, also called slow wave sleep or N3, is the most physically restorative stage of the night. This is when growth hormone peaks. Blood pressure drops to its lowest point. The immune system consolidates. Muscle and tissue repair happens. Metabolic waste begins to clear.

It's also the stage where declarative memory (facts, events, personal experiences) gets transferred from the hippocampus (short-term storage) to the cortex (long-term storage). Sleep spindles, the bursts of brain activity generated during deep NREM sleep, are the mechanism. Without enough of them, what you learned or experienced during the day doesn't stick the way it should.

Adults need roughly 15 to 25 percent of their total sleep in deep sleep. For someone sleeping seven hours, that translates to approximately 75 to 105 minutes. My average over the past year has been 50 minutes, trending down from 54 minutes to 43 minutes over the most recent 90-day window. That decline is the thing I'm paying attention to.

Part of this is biology. We lose approximately two percent of our deep sleep capacity per decade starting in our 30s. By 55, this is an active trend that requires active countermeasures. It doesn't have to be the story, but ignoring it makes it one.

What REM Sleep Does And Why Losing 1% Raises Dementia Risk by 9%

REM sleep is where the cognitive and emotional restorative work happens. The brain during REM looks, on an EEG, almost identical to the brain during waking. It's not resting. It's processing.

Emotional memories are replayed and integrated during REM, but the emotional charge is stripped in the process. Matthew Walker, author of "Why We Sleep" (which I think should be required reading for all humans) describes this as "overnight therapy." Procedural memory (skills, patterns, motor sequences) is consolidated here. Creative and associative thinking is generated as the brain makes novel connections across disparate memory networks.

The cardiovascular system goes through dramatic cycling during REM: massive activation, then silence, then activation again. This cycling is considered essential for cardiovascular health, though it is one of the least discussed functions of this stage.

Then there is the dementia data. Research published in JAMA Neurology and cited by Harvard Health found that for every one percent reduction in REM sleep, dementia risk increases by approximately nine percent. That's not a marginal signal. A person sleeping seven hours with 10 percent REM instead of 20 percent is carrying meaningfully higher neurological risk, all else equal.

My average REM over the past year has been approximately one hour, trending down from 66 minutes to 55 minutes over the most recent 90 days. One hour represents about 14 percent of my total sleep. The target is closer to 20 to 25 percent, roughly 90 to 110 minutes at my sleep duration. I have room to improve here, and the trajectory is moving in the wrong direction. That's useful information.

How Sleep Cleans Your Brain: The Glymphatic System

This is the piece of sleep science that changed how I think about the whole thing.

The brain has its own waste clearance system, called the glymphatic system. It's a network of fluid channels that flushes metabolic waste, including amyloid-beta and tau proteins, out of the brain and into the bloodstream. It operates almost exclusively during sleep, primarily during deep sleep, when brain cells shrink by approximately 60 percent to allow cerebrospinal fluid to flow more freely through the spaces between them.

Amyloid-beta and tau are the two proteins that accumulate in Alzheimer's disease. A 2025 study published in Nature Communications, a randomized crossover trial with 39 participants, confirmed that glymphatic clearance during normal sleep measurably increased plasma levels of these proteins compared to sleep deprivation, meaning the proteins were being moved out of the brain. When sleep was restricted, clearance was impaired.

Short sleep duration and poor sleep quality are associated with greater amyloid and tau pathology even before any clinical symptoms of cognitive decline appear. This doesn't mean that poor sleep causes Alzheimer's in isolation. But it does mean that chronic impairment of this nightly cleaning process appears to accelerate the accumulation of the proteins we most want to keep cleared.

I think about it this way: every night of good deep sleep is a cleaning crew for my brain. Every night of fragmented or shortened sleep leaves more of that work undone. Over years and decades, that accumulation matters.

What My Oura Data Actually Shows

A note on the tool before the data: the Oura Ring is currently the most validated consumer sleep tracker on the market, tested against polysomnography (the clinical gold standard) at Brigham and Women's Hospital. Its sensitivity for detecting deep sleep is 79.5 percent and for REM is 76 percent. It consistently underestimates REM by four to six minutes. I'm not treating these numbers as clinical diagnoses. I'm treating them as directionally reliable trend data, which is exactly what they are. Trends are what I am managing.

Here's what my full year of data shows:

My sleep duration has been remarkably consistent: between 6 hours 45 minutes and 7 hours 10 minutes most months, going to bed around 10:30 pm and waking at 6am. Consistency is one of the most important variables in sleep quality, and this is genuinely a strength. My circadian rhythm is anchored.

My sleep scores in October and January were my strongest, averaging above 80 with my longest sleep durations of the year. March and April dipped into the high 70s, coinciding with travel across time zones and some of my lightest deep sleep and REM months. The correlation is clear: when deep sleep and REM compress, the whole system softens. My HRV scores told the same story in those months.

The 90-day trend is what I am addressing now. Deep sleep declining from 54 minutes to 43 minutes. REM declining from 66 minutes to 55 minutes. Total sleep holding steady, meaning the issue isn't duration. It's stage distribution. Something is compressing the most restorative phases of my night.

I have a reasonable hypothesis about part of it. More on that in the improvement section.

Why My Numbers Are Trending Down, And What Is Actually Driving It

The age factor is real and worth naming honestly. The loss of deep sleep capacity after 50 is documented and significant. This is not a failure. It's biology that requires a response.

But age isn't the whole story here. When I look at my data honestly, a few other variables stand out.

Alcohol is one. I know from direct observation in my own data that more than one glass consistently disrupts my sleep architecture, specifically the second half of my night, which is when most REM occurs. Alcohol sedates the first half of the night and fragments the second, suppressing the long REM periods that should be accumulating in hours five, six, and seven. This is well established in the research, and I see it clearly in my own numbers on nights when I've had more than a single drink. I manage this, but not always perfectly.

Travel is another legitimate variable. Multiple time zone shifts across the year compressed my averages in ways that a domestic schedule would not. I account for this when reading my data.

How to Get More Deep Sleep: What the Research Actually Supports

There’s a lot of noise in the sleep optimization space, but these are the interventions with the strongest evidence now.

The warm bath or shower, timed correctly. A meta-analysis in Sleep Medicine Reviews found that passive body heating one hour before bed increases slow wave sleep by 15 to 36 percent across age groups. That's one of the largest effect sizes of any non-pharmacological sleep intervention in the literature. The mechanism: warming the body triggers compensatory cooling through vasodilation in the hands and feet, which is one of the primary physiological signals for sleep onset and deep sleep entry. The timing matters. It needs to be 60 to 90 minutes before sleep, not immediately before, to allow the cooling response to develop. I've been aware of this research for some time, but haven't been consistent about applying it because showering just before bed is more convenient. That changes now.

Resistance training. Of all exercise modalities, resistance training produces the strongest evidence for increasing deep sleep specifically. Moderate aerobic exercise also helps.

For multiple reasons I'll discuss throughout this series, resistance training is something I need to do more of. The caveat is timing: high-intensity training within three to four hours of bed can elevate cortisol and delay deep sleep onset.

Consistent wake time above all else. Sleep pressure, the accumulation of adenosine in the brain during waking hours, is the primary driver of deep sleep depth. A consistent wake time builds predictable sleep pressure. This is more important than bedtime, and it's something I already do well.

Glycine, 3 grams before bed. This is the supplement I'm adding. Multiple controlled trials show that 3 grams of glycine before bed shortens the time to reach slow wave sleep, improves subjective sleep quality, and improves next-day cognitive performance. The mechanism overlaps with the warm bath: glycine lowers core body temperature. I already take magnesium glycinate, which helps, but the glycine dose in magnesium glycinate is lower than the therapeutic 3-gram dose used in the research. These work through complementary pathways and are worth stacking.

Magnesium glycinate. Already in my protocol. A 2025 randomized controlled trial found significant improvements in insomnia severity within 14 days with 250mg elemental magnesium and 1,523mg glycine combined. My magnesium glycinate with Chelamax covers the magnesium side well.

How to Improve REM Sleep: The Most Underestimated Lever

The single most impactful thing most people can do for REM is protect total sleep time, particularly the last 60 to 90 minutes of the night. REM is loaded into the back end of the sleep cycle. Cutting sleep short by even one hour eliminates a disproportionate amount of REM: not deep sleep, not light sleep, but specifically the long REM periods that should be accumulating in the final cycles.

For someone sleeping 10:30pm to 6am, going to bed earlier a few nights per week would add meaningful REM time. Small extension, significant impact on the stage that matters most for brain health.

The other levers with strong evidence:

Reduce alcohol, especially on consecutive nights. The mechanism is specific: alcohol suppresses REM in the second half of the night as blood alcohol drops, triggering a rebound of lighter fragmented sleep precisely when deep REM periods should be occurring. Even one to two drinks produces measurable disruption. I'm not advocating abstinence. I am saying the data is clear about what a consistent single glass versus two or three does to my own REM numbers, and I find that useful information to hold.

Evening light environment. Research published in PMC found that blue-light-depleted evening environments significantly increase REM duration and reduce REM fragmentation. I already log off tech by 7:30 to 8pm most nights. This is one of the better habits I have, and the data likely reflects it.

Stress processing and nervous system state before bed. Unresolved physiological stress, measurable as low pre-sleep HRV, directly fragments REM. This is where breathwork, HeartMath coherence practice, and whatever helps you genuinely downregulate before sleep become relevant. I use a GABA-l-theanine product on nights when I feel more alert than I'd like. The research on GABA and l-theanine for sleep onset is solid. Timing matters: 30 to 60 minutes before sleep is the effective window.

Hormone Replacement Therapy. A note on my progesterone: progesterone is a natural GABA-A receptor agonist, meaning it supports the same inhibitory pathway that sleep medications and GABA supplements work through. I've recently added progesterone as part of my HRT protocol and it's likely contributing meaningfully to my sleep quality in ways my scores will reveal. This will come up again when I talk about HRT and longevity. 

The Sleep - Heart Rate Variability (HRV) Connection

HRV is the next metric in this series. I want you to understand, going in, that it's not an independent variable. It's partly a readout of how well you are sleeping.

My Oura data shows something I want to name explicitly before we move on: months with lower deep sleep and REM correlate directly with a softening of my HRV. March and April, my lightest sleep months, also showed the most HRV readings in the "Good" or "Fair" range rather than "Optimal."

This isn't a coincidence. Poor sleep quality directly suppresses HRV by increasing sympathetic nervous system activity. Fragmented sleep means more nighttime awakenings, each one producing a spike of sympathetic activation that lowers HRV. Once sleep improves, HRV likely improves with it.

The birthday approaches! The audit continues.

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