Two to three minutes in water below 4°C lowered young men's testosterone by about 19%
A 2025 PLoS One study put 13 Polish physiotherapy students with no winter swimming experience into an ice-water tub inside a refrigerated truck and drew blood before and after.
The paper
Single immersion in cold water below 4 °C: A health hazard in young healthy men?
Teległów A, Cicha I. PLOS One, 2025;20(5):e0324502.
See the study at a glance
- Design
- Single-group before-and-after study
- People
- 13 young men (12 analyzed)
- Who they were
- Healthy male physiotherapy students aged 21–25 in Poland. None had winter swimming experience.
- What they did
- Two to three minutes in a tub of water below 4°C inside a refrigerated truck with air at −15°C. The whole cold exposure lasted about 5 minutes, and blood was drawn before and within 7 minutes after.
- How long
- One session
These numbers came out of it
−19%
Total testosterone fell from 21.22 to 17.27 nmol/L. The average stayed within the normal range.
No change
Cortisol and thyroid-stimulating hormone (TSH) showed no significant change after the dip.
31.55°C
The paper reports a body temperature of 31.55°C after the dip and gives no method or measurement site.
The researchers did this
Thirteen young men who had never swum in winter sat for 2–3 minutes in a tub of water below 4°C. The tub stood inside a refrigerated truck at −15°C. Counting the time in the truck, the whole cold exposure lasted about 5 minutes. A record holder supervised the dips.Source 1 · Clinical trialSingle immersion in cold water below 4 °C: A health hazard in young healthy men?Teległów A, Cicha I. PLOS One, 2025.Read the paper ↗PubMed ↗ The researchers drew blood before the dip and within 7 minutes after it, and 12 men had usable results.
Total testosterone fell from 21.22 to 17.27 nmol/L. That drop of about 19% left the average within the normal range.Source 1 · Clinical trialSingle immersion in cold water below 4 °C: A health hazard in young healthy men?Teległów A, Cicha I. PLOS One, 2025.Read the paper ↗PubMed ↗ Cortisol's shift from 18.91 to 17.45 µg/dl wasn't significant, and TSH held steady.
Several other blood markers moved but stayed within healthy limits. Urea, creatinine, uric acid and chloride fell. Bilirubin and HDL cholesterol rose, as did enzymes such as CK and AST.Source 1 · Clinical trialSingle immersion in cold water below 4 °C: A health hazard in young healthy men?Teległów A, Cicha I. PLOS One, 2025.Read the paper ↗PubMed ↗ The paper reports body temperature falling from 36.45°C to 31.55°C and calls that moderate hypothermia. It doesn't say how or where the temperature was measured, and a person's core can't plausibly cool that much in 2–3 minutes.
The study can't tell you these things
- It had no control group, so each man's results are compared with his own from minutes earlier.
- Blood was drawn within 7 minutes of the dip, and shifts in plasma volume (the fluid part of the blood) could change hormone concentrations by themselves.
- The temperature reading behind the reported hypothermia has no stated method or site.
- It tested one dip in young men, so it can't say what regular plunging does to testosterone.
We cited these sources
- 01Teległów A, Cicha I. Single immersion in cold water below 4 °C: A health hazard in young healthy men?. PLOS One. 2025;20(5):e0324502. doi:10.1371/journal.pone.0324502 PMID 40408371