BACKGROUND AND PURPOSE:

• Core temperature is reduced in menopause
• A current theory maintains that slight elevation in core temperature will trigger a hot flush
• Jones et al. (Menopause, 2019) examined whether the above view is correct regarding the core temperature increase as a cause of hot flushes

METHODS:

• Secondary analysis of 5 previous studies
• Participants
  • symptomatic postmenopausal women
• Exposures
  • Resting state: Wearing a tube-lined suit, perfused with 34°C water
  • Mild heat stress: Suit perfused with 48°C water
• Measurements (continuous) of the following
  • Sweat rate | Skin blood flow | BP | Heart rate | Skin temperature | Core Temperature
• Hot flush definition
  • Abrupt, spontaneous increase in sternal sweat rate during rest and mild heat stress 
• A subset of women underwent whole-body passive heating for 60 minutes
  • Threshold studies: Temperature at which cutaneous vasodilation (core body temp) and/or sweating (mean body temp) begins
  • Sensitivity studies
    • For sweating, slope of relationship between sweat rate and body temperature
    • For vasodilation, slope of relationship between skin blood flow change and core temperature
  • Compared to premenopausal women

RESULTS:

• 72 postmenopausal women | 108 hot flushes
  • Mean age: 45.8 ± 5.1 years
  • BMI: 25.9 ± 4.5 kg/m²
• Spontaneous hot flush
  • In the 20 minutes before a spontaneous hot flush, core temperature increased by 0.03 ± 0.12°C (P < 0.05)
  • Only 51% of hot flushes were preceded by an increase in core temperature
• Mild heating
  • 76% of hot flushes were preceded by an increase in core temperature
• Subset analysis of postmenopausal vs premenopausal women undergoing passive heating for 60 minutes
  • Sweating thresholds: Similar between post and premenopausal women
  • Vasodilatory threshold was higher in postmenopausal women (P = 0.06)
    • Postmenopausal: 37.1 ± 0.2°C
    • Premenopausal: 36.8 ± 0.3°C

CONCLUSION:

• The authors conclude that the evidence does not support core temperature as a trigger of hot flushes based on the following
  • Not all hot flushes are preceded by change in core temperature
  • Similar sweating thresholds between post and premopausal women
• Postmenopausal women need a higher core temperature before vasodilation occurs, suggesting that this cohort may be less efficient at dissipating heat
• The authors state that exercise has been shown to reduce the frequncey and severity of hot flashes and in addition

…recommendations for women to avoid conditions that may increase their core temperatures and to avoid/not perform exercise should be reconsidered 

Learn More – Primary Sources:

Is core temperature the trigger of a menopausal hot flush?

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