Heat exposure elevates plasma immunoreactive growth hormone-releasing hormone levels in man.
Level 3 - non-randomized controlled study
Non-randomized comparative physiological cohort study with an age-based comparator group
PubMed 3117831 · doi:10.1210/jcem-65-5-1035
What was done
Twelve healthy men—six younger (31–46 years) and six older (49–66 years)—underwent acute heat exposure for 15 minutes in a Finnish sauna bath at an ambient temperature of 72°C. Rectal temperature was monitored, and serial plasma samples were collected to measure growth hormone (GH) and immunoreactive growth hormone-releasing hormone (GHRH) via radioimmunoassay after Sep-Pak C18 cartridge purification (recovery 62 ± 10%). Circulating GHRH molecular forms were characterized using reverse-phase high-pressure liquid chromatography (RP-HPLC).
What was found
In younger men, 15 minutes of sauna exposure raised rectal temperature by 0.2°C. Plasma immunoreactive GHRH increased from 9 ng/L at baseline to 36 ng/L at 5 minutes post-exposure (P < 0.05) before returning to baseline by 45 minutes. Plasma GH increased from 2 µg/L to 5 µg/L at 30 minutes (P < 0.01). In older men, no significant increases in plasma GH or GHRH levels were observed after heat exposure. RP-HPLC analysis indicated that the predominant circulating form was GHRH-(1-40).
Why it matters
This study provides physiological evidence in humans that acute heat-induced growth hormone release is mediated upstream by GHRH, and shows that this neuroendocrine response is blunted or lost with aging.
Limits
The sample size is very small (n = 12 total, 6 per age group), restricted exclusively to men, and lacks a time-matched non-heat control condition. Somatostatin and other regulatory hormones were not measured.
Cited by
- supports Deliberate heat exposure in a sauna increases growth hormone levels.
- supports Exercise, deliberate heat exposure, and intermittent fasting have all been shown to increase growth hormone.
- supports Higher sauna temperatures and longer durations produce a more robust growth hormone response, up to 200° Fahrenheit.