Introduction: In the US, 1.3 million women enter menopause yearly: ~80% experience hot flashes (HFs), 40-60% report insomnia, and 83% report HF-related sleep interference with daytime productivity. Often, menopausal symptoms are treated with hormone replacement therapy (HRT), including HFs, which often occur due to a narrowing hypothalamic thermoneutral zone and hyperactive temperature-sensitive brain neurons. Previously, we showed that the Eight Sleep Pod, an actively temperature-regulated mattress cover (ATR), can reduce HFs by ~52%. However, we did not explore potential mechanisms driving this reduction. We hypothesized that sleeping with ATR might increase thermoneutral zone duration, thus reducing HFs. Objective: This study explored whether ATR reduced HFs by lowering core and skin temperatures during sleep. We also explored whether HRT use modified the relationship between HFs and reported menopausal symptoms. Methods: Peri- and post-menopausal women (n=98, 54.1±6.7 y; HRT n=35; non-HRT n=51) completed 7 nights each of ATR OFF (temperature regulation disabled) and ATR ON (all-night active temperature regulation) in randomized (n=60) or fixed (n=38) order (1,964 total nights). During each ATR condition, n=60 postmenopausal women recorded core temperature via gastrointestinal pill (Tc) on Night 3 out of 7, along with foot and chest temperatures on Nights 2-4. The distal-proximal-gradient (DPG), a marker of skin temperature uniformity during sleep, was calculated by subtracting the chest from foot temperature. Daily outcomes included reported nocturnal HF frequency and perceptual ratings. After each week of ATR ON and OFF, participants completed the Menopause Rating Scale and Pittsburgh Sleep Quality Index. Paired comparisons (t-tests, Wilcoxon signed-rank tests) evaluated differences between ATR conditions. Linear mixed-effects models examined how temperature parameters (Tc and DPG) impacted HFs. Results: ATR ON reduced nocturnal HFs by 57% on average, independent of HRT use (means±SD: HRT= -57±39.4%; no HRT= -58±34.6%). ATR ON increased time spent with Tc < 36.5°C by 23.8±3.6% and DPG < -1°C by 28.4±3.5% (both means±SE; P< 0.001). With ATR ON, 23% (12/53) and 24% (14/59) of women spent at least 50% more sleep time with DPG < -1°C and Tc < 36.5°C, respectively. During ATR ON, overall menopause symptom severity decreased by 2.8±5.0 out of 44 points, and sleep quality increased by 1.4±2.5 out of 21 points (both P< 0.001); improvements were observed regardless of HRT use. On nights with fewer HFs, women reported more comfortable body temperatures (r= -0.6) and higher sleep satisfaction (r= -0.5, both P< 0.01). Conclusion: Independent of HRT use, sleeping with ATR ON reduced nocturnal HFs by more than half, improved sleep quality, and alleviated menopausal symptom severity. Our data indicate that one mechanism by which ATR reduces HFs is by increasing the time spent maintaining a wider gradient (DPG) between the foot and chest temperatures and TC. This is the first study we are aware of that demonstrates two thermal mechanisms by which ATR reduces HFs. This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.
Holm et al. (Fri,) studied this question.