Does acute heat stress alter lactation performance in postpartum mothers?

Abstract

Introduction: Heat stress has been shown to acutely decrease lactation performance in various mammalian species, however whether a similar effect is present in humans remains largely unexplored. Objective and hypothesis: The objective of the present study was to determine whether an acute whole-body heat stress reduces lactation performance in postpartum mothers in the proceeding 24 h. Methods: To date, 9 postpartum mothers (32±4 y; 1.6 ±0.1 m; 67±13 kg; 8±3 months postpartum) have participated in the study. During the 24 h period before and after the acute passive heat stress, participants were asked to record their voluntary fluid intake and their milk production defined as the volume of expressed milk and/or breastfeeding volume based on the baby’s weight before and immediately after nursing, accounting for evaporative water losses. The passive heat stress protocol involved participants laying supine while donning a tube-lined garment continuously perfused with 49°C water for 60 minutes. Rectal temperature and heart rate were measured during the passive heat stress intervention to confirm thermal strain, and whole-body sweat losses were calculated as the net difference in body mass following passive heat stress. Results: The 60-minute passive heat stress protocol increased rectal temperature by 0.4±0.3°C, increased heart rate (17±12 BPM), and resulted in a whole-body sweat loss of 278±201 g. The frequency of lactation was similar during the 24 h before (5.4±1.6 times) and 24 h after (5.1±1.1 times, P=0.20) acute passive heat stress. The total volume of human milk production in the 24 h prior to heat stress was not different to the 24 h following heat stress (pre: 327±123 ml, post: 312±148 ml, P=0.33). Maternal fluid intake was higher during the 24 h after passive heat stress (1561±73 ml) in comparison to the 24 h before (1377±244 ml, P=0.05). Conclusion: Preliminary data suggests that an acute bout of whole-body heat stress does not modulate lactation performance in postpartum mothers. This research was supported by Dr. Ravanelli’s Natural Sciences and Engineering Research Council of Canada Discovery Grant (PIN#2022-05096). This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.