Subjective menopausal hot flashes in sleep disturbance: does the timing of hot flashes matter?

OBJECTIVES: Understanding the association between hot flashes and sleep disturbance is complicated, given that various dimensions of hot flashes (ie, occurrence, frequency, severity, timing) may have different associations with sleep. We evaluated the associations between various dimensions of momentary hot flashes and sleep disturbance (ie, sleep onset latency, sleep quality). We examined whether daytime, evening, and nocturnal hot flash frequency and/or severity predicted sleep disturbance. METHODS: Participants (N=99) completed self-report measures of hot flashes and sleep for seven consecutive days. Participants retrospectively reported the number and severity of daytime (reported each morning and afternoon), evening (reported each evening), and nocturnal (reported each morning) hot flashes they had, and completed a sleep diary each morning. We conducted a series of linear mixed-effects models regressing both sleep outcomes onto daytime/evening hot flash frequency/severity, and regressing sleep quality onto nocturnal hot flash frequency/severity. RESULTS: Results indicated that within-person evening hot flash severity was associated with sleep onset latency (Est=5.60, SE=2.48, 95% CI [0.75-10.46], P<0.05), and that within-person nocturnal hot flash frequency was associated with sleep quality (Est=-0.46, SE=0.06, 95% CI [-0.58 to -0.34], P<0.001). CONCLUSIONS: We found that more severe evening hot flashes predicted longer sleep onset latency that night, and that more frequent nocturnal hot flashes were associated with worse sleep quality that night. This may suggest that targeting hot flashes that occur at night-both in the evening before bed and nocturnally during sleep-may be useful in improving sleep in perimenopausal and early postmenopausal women.