I Tracked My Cortisol and Testosterone for 90 Days — Here's What Stress Actually Does to Your Hormones

Ninety days ago I had my cortisol tested on a whim, alongside the standard testosterone panel my doctor runs annually. The testosterone came back at 412 ng/dL — technically “normal,” technically fine. But the cortisol was 23 mcg/dL at 8am, and my DHEA-S was in the bottom quartile for my age group.

That combination told a story the single testosterone number was hiding.

The Axis Nobody Explains to You

The hypothalamic-pituitary-adrenal (HPA) axis and the hypothalamic-pituitary-gonadal (HPG) axis share real estate in the brain. When the HPA axis runs hot — chronic work stress, poor sleep, high training volume without adequate recovery — it releases cortisol. That cortisol, at chronically elevated levels, has a measurable suppressive effect on LH (luteinizing hormone), the upstream signal that tells your testes to produce testosterone.

A 2021 meta-analysis in Frontiers in Endocrinology reviewing 19 studies found that sustained cortisol elevation above 18 mcg/dL was associated with a 15–22% reduction in free testosterone even when total testosterone stayed within range. This is the critical distinction most conventional hormone panels miss: total testosterone can look fine while free testosterone — the biologically active fraction — is quietly suppressed.

Cortisol also upregulates sex hormone-binding globulin (SHBG), the protein that binds testosterone in the bloodstream and makes it unavailable to tissues. A Stanford study on endurance athletes found that four weeks of training overreach (volume without adequate recovery) raised SHBG by 18% and reduced free testosterone by 24%, without meaningfully changing total testosterone.

What I Tested For 90 Days

I’m not a doctor. I’m a 38-year-old who spent a decade in competitive cycling before pivoting to desk work and watching my energy, sleep quality, and recovery slowly degrade. My doctor was satisfied with a number on a lab sheet. I wasn’t.

The protocol I ran, loosely based on work from Dr. Molly Maloof’s longevity clinic and adapted from research by Kyle Gillett, MD (a hormone specialist who publishes detailed protocols on his podcast), involved four levers:

1. Cortisol blunting via sleep architecture The first two weeks I made zero changes to diet or exercise. I focused only on sleep: 10pm lights out, no alcohol, blackout curtains, keeping the room at 67°F. The goal was increasing slow-wave sleep, which is when the bulk of testosterone pulse secretion occurs. Using my Oura Ring to track, I went from averaging 52 minutes of deep sleep to 81 minutes over two weeks.

2. Training structure shift I dropped my weekly Zone 2 volume from 8 hours to 5 hours and added two sessions of heavy compound lifting (squat, deadlift, bench, press). Research from the Journal of Strength and Conditioning Research confirms that heavy resistance exercise acutely raises testosterone and GH, while excessive steady-state cardio without recovery days reliably suppresses it.

3. Zinc and vitamin D optimization I was vitamin D deficient at baseline — 24 ng/mL. A randomized controlled trial published in Hormone and Metabolic Research (Pilz et al., 2011) found that supplementing vitamin D3 in deficient men raised total testosterone by an average of 25% over 12 months. Zinc depletion (common in endurance athletes through sweat loss) impairs the enzymatic conversion of cholesterol to testosterone. I added 5,000 IU D3 with K2 and 15mg zinc glycinate daily.

4. Intermittent fasting reframe I had been skipping breakfast and training fasted — a popular biohacking practice that, for people under significant cortisol load, appears to compound the problem. A 2022 study in Nutrients found that prolonged fasting windows in stressed individuals raised morning cortisol AUC (area under the curve) by 14%. I switched to eating within 90 minutes of waking.

The Numbers at Day 90

I ran a full panel through Marek Health at the 30-day and 90-day marks. Here’s what changed:

The total testosterone number looks modest — 412 to 503, roughly a 22% increase. But the free testosterone jump is more meaningful: from 9.1 to 14.8 pg/mL is a 63% increase in the hormone that actually reaches androgen receptors and does things. The main mechanism wasn’t testosterone production going up dramatically — it was SHBG going down and cortisol coming down, freeing up more of what was already there.

What This Means If You’re Testing “Normal”

The normal range for testosterone on most US lab reports is 300–1000 ng/dL. That range was derived from a population sample that included sedentary men, men with metabolic syndrome, and men across a 50-year age span. “Normal” is not the same as “optimal.”

If you’re in the 350–500 range with symptoms — low energy, slow recovery, brain fog, reduced libido, difficulty maintaining muscle — the number alone isn’t enough information. You need:

• Free testosterone (calculated or direct) — not just total
• SHBG — elevated SHBG can explain low free T even with adequate total T
• Morning cortisol — ideally a four-point salivary cortisol test, though a single 8am blood draw gives a rough signal
• DHEA-S — the adrenal precursor; often suppressed alongside cortisol dysregulation
• Vitamin D — deficiency is independently associated with testosterone suppression in multiple RCTs

None of this requires a specialist. What it requires is knowing what to ask for.

The Variables I Didn’t Control

This was an n=1 experiment with real limitations. I changed multiple things simultaneously, so I can’t attribute the improvements to any single intervention. Vitamin D correction alone may account for a significant portion of the testosterone increase, based on the Pilz study. The sleep changes may have driven the cortisol shift more than the fasting window adjustment.

What I can say is that the intervention bundle worked, and each component has independent RCT support. The subjective experience — energy, mood, recovery — shifted noticeably around weeks five and six, before the second blood draw confirmed anything numerically.

Where to Start If You Want to Run Your Own Version

If you’re a man over 35 experiencing these symptoms, the lowest-effort, highest-yield starting point is:

1. Get a full hormone panel that includes free testosterone, SHBG, DHEA-S, and vitamin D. Use Marek Health, Blokes, or Maximus Labs if your PCP won’t order them.
2. Fix your sleep before changing anything else. No supplement stack outperforms 80+ minutes of deep sleep.
3. Check vitamin D. If it’s below 40 ng/mL, supplement. This is one of the clearest hormone interventions in the RCT literature.
4. Audit your training load. Chronic cortisol elevation from overtraining is a direct suppressor of the testosterone axis.

The hormonal system isn’t a single dial you can turn up. It’s a network, and the variables that drive it down are often things you don’t associate with hormones at all — stress, sleep debt, low vitamin D, and too much cardio with too little recovery.

Understanding that changed the way I approach the whole system.