Total testosterone declines by approximately 1–2% per year from the age of 30. By 60, average levels are 30–40% lower than at peak. This decline is real, measurable, and has consequences for muscle mass, bone density, energy, mood, and cardiovascular health.
But the rate and severity of that decline is highly variable — and much of that variability is explained by lifestyle factors that are within your control.
Sleep: the most underappreciated factor
Testosterone is primarily produced during sleep, concentrated in the REM and early slow-wave sleep stages. A single week of sleeping 5 hours per night reduces testosterone levels by 10–15% in young healthy men. Chronic sleep restriction produces sustained suppression.
Training: what works, what doesn't
Resistance training acutely and chronically elevates testosterone. The strongest stimulus is compound, heavy lifting — squats, deadlifts, presses — with moderate to high volume. Excessive endurance training (particularly high-volume running) can suppress testosterone, likely through cortisol elevation and energy deficit.