How does heat affect prolactin?

Heat exposure, specifically through sauna use, significantly increases prolactin levels. Dr. Rhonda Patrick describes how heat stress leads to a substantial elevation of prolactin, which is known for its role in lactation and other functions including sleep regulation. For instance, men who stayed in an 80 degrees Celsius sauna until exhausted experienced a tenfold increase in prolactin levels, while women who spent 20 minutes in a dry sauna twice a week saw a 510% increase in prolactin levels after each session. These heightened prolactin levels last for a couple of hours and are suggested to help promote slow wave sleep, the deepest phase of non-REM sleep 1 .