Monthly variation of hot flashes, night sweats, and trouble sleeping: effect of season and proximity to the final menstrual period (FMP) in the SWAN Menstrual Calendar substudy

Abstract

Although reproductive function is influenced by season, few studies have evaluated seasonal effects on menopausal symptoms. We assessed the impact of season and proximity to the final menstrual period (FMP) on frequency of symptom reporting. 955 participants in the Study of Women’s Health Across the Nation recorded whether or not they had experienced menopausal symptoms on a monthly menstrual calendar over a 10-year period. We modeled the log-odds of presence of a given symptom each month using a logistic mixed effects model, assuming a 3 rd -order polynomial before the FMP and a different 3 rd -order polynomial after the FMP. We assumed sine and cosine functions for month of the year. 5–10 years prior to the FMP, ~20% of women reported hot flashes and night sweats while ~40% reported trouble sleeping. Prevalence rose ~4 years before the FMP with a sharp jump in hot flash (~60%) and night sweats (~40%) prevalence coincident with the FMP. Peaks in hot flashes and trouble sleeping were observed in July with troughs in January. The peak and trough in night sweats occurred about one month earlier. Odds of hot flashes, night sweats and trouble sleeping were 66%, 50% and 24% greater, respectively, at the seasonal peak versus the seasonal minimum. Menopausal symptoms exhibit seasonal variation associated with the summer and winter equinoxes. Seasonal increases in night sweats precede increases in hot flashes. Prospectively recorded monthly symptom data demonstrate that hot flashes and night sweats increase notably coincident with the FMP.