Professor Thomas Seager says his testosterone went from 750 to 1,180 nanograms per deciliter after incorporating cold plunging into his routine. That's a 57 percent increase in a man in his mid-fifties. The headline is compelling, the numbers are real, and the mechanism he points to — mitochondrial optimization — is genuinely well-supported. But this is also a single person's experience, and it's worth understanding what the research actually says before you start treating cold water as a testosterone clinic.
The knowledge base has a few relevant threads here. One article references a neuroscientist claiming a 250 percent increase in testosterone from cold showers — a figure that would require extraordinary evidence to believe. Seager's numbers are more modest and more plausible. A 2026 recovery study in the database shows meaningful increases in both testosterone and cortisol after repeated exercise stress, which aligns with a broader principle: hormetic stress, applied consistently, tends to upregulate the systems you're stressing.
The mitochondrial angle is where Seager is on firmest ground. Cold exposure triggers mitophagy — the clearance of damaged mitochondria — and stimulates mitobiogenesis, the generation of new ones. Healthier mitochondria produce ATP more efficiently. And because testosterone synthesis in the Leydig cells of the testes is an energy-intensive process, mitochondrial health and androgen production are genuinely linked. It's not a straight line from "cold water" to "more testosterone," but the pathway is real.
The biggest point of contention isn't whether cold exposure affects testosterone — it's when you do it. Seager's protocol involves cold before exercise. That's important. Cold exposure after resistance training suppresses the inflammatory cascade that drives muscle protein synthesis. You're essentially signaling your body that the damage is already repaired, before the adaptation has a chance to happen. Studies consistently show that cold-after-lifting reduces hypertrophy over time. If you're training for strength or muscle mass, cold is a morning tool, not a post-workout one.
If you're interested in the testosterone angle, timing matters. Cold plunge in the morning, before any strength training, or on rest days. Aim for water between 40 and 55 degrees Fahrenheit, two to four minutes, three to five times per week. The frequency builds the adaptation. A single heroic plunge does less than a consistent moderate practice over months.
Seager's line — "a man is only as old as his mitochondria" — sounds like a soundbite, but it points at something profound. Mitochondrial decline is one of the most consistent biological signatures of aging across every tissue we've studied. Sauna research in the knowledge base shows similar mitochondrial benefits through heat shock proteins. Cold and heat are operating on the same underlying system from opposite directions. One stresses the cell with cold, one with heat. Both trigger clearance of damaged components and stimulation of new ones. The contrast therapy protocol — alternating between the two — may be more powerful than either alone, not because of the temperature swing, but because you're hitting the same mitochondrial renewal pathway twice in one session.