Hot flashes and circadian rhythms of body temperature, rest/activity and mood in post-menopausal women

Introduction: Menopause marks the end of fertility in women. Besides mood changes at the end of the menstrual cycles in middle-aged women, some start presenting hot flashes. Objective; verify possible correlations between peripheral temperature, rest/activity and mood rhythms and the presence of hot flashes in post-menopausal women. Methods: We studied three groups of women, two of which comprised patients from the Hospital das Clínicas de São Paulo; i) post-menopausal women with hot flashes (n=13), on average 55 (±4) years old; ii) post-menopausal women without hot flashes (n= 6) 59 (±1.5) years old. A control group featured 10 women on average 36 (±4) years old. For 30 consecutive days volunteers recorded motor activity of the arm, wrist skin temperature and hot flashes episodes by Tempatilumi; in addition, the subjects kept a sleep diary, and two visual analog scales (anxiety and joy) for self-evaluation of mood states every 3 hours and in the moment of a hot flash. All subjects completed the Horne-Ostberg questionnaire of chronotypes. Data for motor activity, temperature, hotflash occurrence and mood were submitted to spectral analysis. Rhythmic parameters were determined by the Cosinor or Rayleigh method. The program El Temps was used to draw actograms to visual inspection of the variable over time. Comparisons between groups were quantified by the t-test, or nonparametric alternatives where necessary. Correlations between variables were quantified by Pearson's r or Spearman’s Rho. A significance level of 5% was assumed in all trials. Results: In 5 women with hot flashes we notice the presence of a significant circadian component in the occurrence of hot flashes, together with periods greater than 24 hour. Visual inspection of hotflash timeseries suggest an acrofase of hotflashes in the late afternoon, between 16 and 18h. Conclusion: Initial analyses of hotflash occurrences correspond to findings in the literature. The next steps aim at identifying possible correlations with other physiological variables like body temperature, and motor activity, as well as with the recorded behavioural observables. Publication History Article published online: 16 June 2026 © 2009. Brazilian Sleep Academy. This is an open access article published by Thieme under the terms of the Creative Commons Attribution-NonDerivative-NonCommercial License, permitting copying and reproduction so long as the original work is given appropriate credit. Contents may not be used for commercial purposes, or adapted, remixed, transformed or built upon. (https://creativecommons.org/licenses/by-nc-nd/4.0/) Thieme Revinter Publicações Ltda. Rua Rego Freitas, 175, loja 1, República, São Paulo, SP, CEP 01220-010, Brazil