Circadian rhythm of objectively recorded hot flashes in postmenopausal breast cancer survivors

Objective: Similar to the circadian rhythm of core body temperature, hot fl ashes have been found to exhibit a circadian rhythm in healthy, naturally p ostmenopausal women, with a peak in frequency at 18:25 h. However, to date, no studies have evaluated whether this same pattern is found among breast cancer survivors reporting hot flashes. Design: Daily hot flash frequencies were measured among 21 postmenopausal b reast cancer survivors using validated 24-h sternal skin conductance monito ring. Results: Hot flashes were noted in all women, ranging in frequency from 1 t o 30 per 24-h period. A majority of the sample (86%) experienced greater th an or equal to 1 nighttime hot flash, with 48% exhibiting greater than or e qual to 3 but less than or equal to 7 nighttime hot flashes. For the total sample, a modest circadian rhythm was noted with a peak in hot flash freque ncy occurring at 16:10 h. However, significant variability was observed acr oss individual women, and, as a whole, breast cancer survivors demonstrated distorted to obliterated rhythms. Conclusions: Data suggest that hot flashes in postmenopausal breast cancer survivors do not follow the same circadian pattern as previously seen in he althy, naturally postmenopausal women. Findings have implications for (1) u nderstanding the potential for sleep disturbances and fatigue in breast can cer survivors experiencing hot flashes, and (2) future research examining c ircadian rhythms of core body temperature and hot flashes in breast cancer survivors.