How does sauna increase growth hormone?

Repeated sauna heat exposure, interspersed with cooling breaks, can act as a stressor that stimulates growth-hormone release. In one study, subjects used an 80°C (176°F) sauna for 30 minutes four times in a day, with cooling rest between sessions; growth hormone rose as much as 16-fold. 1

• Heat-responsive neurons: The hypothalamus regulates temperature, and the proposed mechanism is that heat-responsive hypothalamic neurons activate growth-hormone-releasing pathways to the pituitary, which then releases growth hormone. 2
• Response diminishes with repetition: In the study, the increase was roughly 3–4-fold by day three, compared with 16-fold on day one; the response declined as the body adapted to repeated heat exposure. 3
• Hot-cool transitions: Alternating sauna exposure with cooling breaks is part of the repeated-heat protocol; the heat-and-cool transitions were described as engaging a process that can build the growth-hormone response. 4