I spent a long time optimising everything except sleep.
I was tracking macros, timing workouts, taking magnesium, reading about peptide stacks — and getting five or six hours a night because life was busy. Work was busy. The kids were busy. Sleep felt like dead time. I'd deal with it later.
Then I actually looked at the data and felt like an idiot.
The Study Every Man Over 40 Should Know
In 2011, researchers at the University of Chicago ran a study that should've been front-page news. Leproult and Van Cauter, published in JAMA, took healthy young men — average age 24, no health problems — and restricted their sleep to five hours per night for one week. Not a month. One week.
Testosterone dropped by 10 to 15 per cent.
To put that in perspective: testosterone declines at roughly 1% per year from age 30. One week of poor sleep caused the hormonal equivalent of a decade of ageing. That's not a rounding error. That's the entire point of this site happening in a single bad week of sleep.
And young, healthy men in a controlled setting managed five hours. Most men over 40 are running on less than that during stressful periods — consistently, chronically, for years.
Why Your Body Produces Testosterone at Night
This is the mechanism, and once you understand it, the priority calculus changes.
Most of your daily testosterone production happens during sleep — specifically during the first few sleep cycles, tied closely to deep sleep (slow-wave sleep, stage 3). Your testes are relatively quiet during waking hours. At night, stimulated by pulses of luteinising hormone from the pituitary, they ramp up production significantly.
Andersen and Tufik's 2008 review in Sleep Medicine Reviews documented this bidirectional relationship clearly: poor sleep reduces testosterone, and low testosterone impairs sleep quality. Once that cycle starts, it compounds. You sleep badly, your T drops, you recover less well, sleep quality worsens further.
The point is: if you're not getting into deep sleep — or not sleeping long enough to cycle through it multiple times — you're simply not producing the testosterone you're capable of producing. No supplement fixes this. There isn't a pill you can take to compensate for consistently cutting short the one process where most of your production happens.
What "Deep Sleep" Actually Means
Not all sleep is equal, which is worth understanding practically.
You cycle through sleep stages roughly every 90 minutes. A complete cycle includes light sleep, deep slow-wave sleep, and REM. In the early part of the night, the cycles are weighted toward deep sleep. In the second half of the night, they weight toward REM.
Both matter, but deep sleep is where testosterone production and growth hormone release peak. Men over 40 naturally get less deep sleep than younger men — it's a real physiological change. That makes the other variables — sleep timing, sleep environment, things you can control — even more important to get right.
Alcohol in the evening is particularly damaging here, because while it might help you fall asleep faster, it actively suppresses deep sleep architecture. You'll clock eight hours and feel like you slept four. That's not subjective — the testosterone data backs it up.
Morning Light: Start Optimising at 7 AM, Not 10 PM
The most counterintuitive thing about sleep optimisation is that the highest-leverage intervention happens in the morning, not at bedtime.
Andrew Huberman's work at the Huberman Lab at Stanford — drawing on established circadian biology, including research by Czeisler and colleagues on morning light entrainment — makes this clear. Getting outside within 30 minutes of waking and spending 10–20 minutes in natural daylight (no sunglasses, facing toward the light source) anchors your circadian rhythm.
Your suprachiasmatic nucleus — the brain's master clock — uses morning light to set the timing of your entire hormonal cascade. When that light signal is calibrated correctly, melatonin rises earlier in the evening (making you naturally sleepy at a sensible time), and your deep sleep phases are longer and earlier in the night.
When it isn't — when you wake up, never see outdoor light, stare at screens all day, then look at your phone at midnight — the entire system gets pushed later. You fall asleep at 1 AM, can't wake up without an alarm, and wonder why you're exhausted.
On overcast UK days, this still works, just with less intensity. In winter, a 10,000 lux light therapy lamp within an hour of waking does the job.
This is free. It requires walking outside. It's also, in my experience, one of the most impactful changes you can make.
The Evening Protocol
Once you've sorted mornings, evenings become the maintenance side. The goal is to not undermine what you've set up.
No bright light after 9 PM. Blue-wavelength light is the main culprit — it suppresses melatonin more effectively than any other wavelength. Screens, overhead lighting, bright kitchens. Dimmers and side lamps are genuinely useful. Blue-light-filtering glasses are an option if you're using screens late, but ideally you're winding down without them.
Bedroom temperature: 18–19°C. Your core body temperature needs to drop 1–2°C to initiate and maintain sleep. A warm room works against this. This is one of the most evidence-supported sleep interventions and one of the most commonly ignored. Blackout curtains matter mainly because light exposure disrupts sleep stages — but temperature comes first.
Magnesium glycinate, 300–400 mg, 60 minutes before bed. Not oxide (causes GI issues), not citrate (works but less gentle). Glycinate. The evidence for magnesium supplementation improving sleep quality is solid — a 2012 trial by Abbasi et al. in the Journal of Research in Medical Sciences found significant improvements in sleep time, efficiency, and early morning awakening in older adults with insomnia. It's not a sleep drug. It supports the underlying processes. Think of it as removing friction, not forcing sedation.
No alcohol within three hours of bed. This one is difficult for a lot of men, myself included at times. The issue is specific: alcohol fragments sleep architecture. You'll be "asleep" but cycling through light sleep rather than reaching the deep stages where testosterone production happens. One large drink before bed and you've effectively lost 20% of your deep sleep. The research on this is not subtle.
HRV as Your Feedback Signal
Heart rate variability is the metric worth tracking if you want to know whether your sleep protocol is actually working.
HRV measures the variation in time between heartbeats. High HRV reflects good parasympathetic tone — your nervous system is recovered and resilient. Low HRV reflects stress, poor recovery, or inadequate sleep.
Most modern wearables measure it: Garmin, Oura Ring, WHOOP, Apple Watch. I use Garmin. After three weeks of consistent morning light and no alcohol before bed, my HRV baseline moved up by about 8 ms. That's a meaningful shift. More importantly, it's objective — not just "I feel better."
If your HRV is consistently below your personal baseline, your sleep isn't recovering you. That's the signal that something needs adjusting. It's a leading indicator, not a lagging one.
The Protocol — In Order of Impact
If you're going to change one thing at a time rather than overhauling everything at once:
1. Morning outdoor light — 15–20 minutes within 30 minutes of waking. Do this for two weeks. The downstream effect on evening sleep quality is real and noticeable.
2. Consistent sleep timing. Bed within the same 30-minute window every night, weekends included. More than an hour of variation between weekday and weekend sleep times fragments your rhythm significantly.
3. Room temperature: 18–19°C. Get blackout curtains too.
4. No screens after 9 PM, or blue-light glasses if unavoidable.
5. Magnesium glycinate, 300–400 mg, an hour before bed.
6. No alcohol after 7 PM if sleep quality matters to you.
7. Aim for 7.5–9 hours. That sounds like a lot. For men over 40, it usually isn't. You know you've got it right when you're waking up before the alarm and not fantasising about going back to sleep.
What Changes When You Actually Do This
The sequence, if you're consistent:
- Week 1: Falling asleep is easier. Less "wired but tired" at bedtime.
- Week 2: Morning energy is more reliable. The alarm isn't as brutal.
- Week 3: Workout recovery improves. You're not grinding through training sessions feeling half-dead.
- Week 4: Mood is noticeably more stable. Libido starts coming back online. Mental clarity is sharper.
These are testosterone and growth hormone effects. They're not placebo. Get a hormone panel before you start, run the protocol for eight weeks, retest. Most men see measurable improvement from sleep alone.
Everything else — training, nutrition, supplements, protocols — sits on top of this foundation. If the foundation is broken, you're fighting the biology rather than working with it.
Start tomorrow morning. Go outside.