Heat stress and cardiovascular, hormonal, and heat shock proteins in humans.

Plain-language summary

This study set out to see whether heat on its own triggers some of the same responses in the body as exercise. Twenty-five healthy young adults, 13 men and 12 women, sat in a heat chamber at 73 degrees Celsius, which is 163 degrees Fahrenheit, for 30 minutes, and on a separate day sat in the same chamber with no heat at 26 degrees Celsius, which is 79 degrees Fahrenheit. Heart rate, blood pressure and blood markers were measured before and after each. The heat raised core body temperature by 0.8 degrees Celsius, which is 1.4 degrees Fahrenheit, raised heart rate, lowered blood pressure, and pushed up norepinephrine, prolactin (a pituitary hormone that suppresses testosterone when it runs high, so a steady level is the one you want) and heat shock protein 72 (HSP72, a protein cells make to protect themselves under stress). Nothing moved on the no-heat day, which is what makes the heat the cause of the changes rather than the sitting.

Key findings

• Core body temperature rose 0.8 degrees Celsius, which is 1.4 degrees Fahrenheit, after 30 minutes at 73 degrees Celsius, which is 163 degrees Fahrenheit.
• Heart rate rose to 131 beats per minute.
• Systolic blood pressure fell by 16 mm Hg and diastolic by 5 mm Hg.
• On the no-heat control day at 26 degrees Celsius, which is 79 degrees Fahrenheit, none of the heart or blood measures changed at all.