Earlier bedtime misalignment is associated with increased severity of chemotherapy-induced hot flashes in premenopausal women with breast cancer.

Chemotherapy-induced hot flashes (CIHFs), a vasomotor symptom that has been demonstrated to impair the quality of life in breast cancer patients, have been associated with circadian rhythms. While circadian misalignment has been shown to contribute to chemotherapy-related adverse effects, the link between bedtime misalignment (BM) and these effects remains unclear. The objective of this study was to evaluate BM based on objective measurements and determine whether CIHF severity differs according to BM. A total of 35 premenopausal women with breast cancer awaiting chemotherapy were evaluated for BM using actigraphy. Participants were categorized into the earlier misaligned group ("going to bed earlier than preferred bedtime") and the aligned/later misaligned group ("going to bed at or later than preferred bedtime"). CIHF was assessed using 7-day diaries at baseline, at one month post-chemotherapy (T1), and at nine months post-chemotherapy. The habitual bedtime (p = 0.032) and the degree of BM (p < 0.001) measured by actigraphy differed between the earlier misaligned group and the aligned/later misaligned group. The earlier misaligned group reported significantly higher burden of CIHF, including total hot flash score (p = 0.004), daytime and nighttime sweating scores (both p < 0.001), and daytime hot flash frequency (p = 0.007) compared with the aligned/later misaligned group at T1. Premenopausal women whose habitual bedtime was earlier than their preferred bedtime experienced greater burden of CIHF. Our findings indicate the potential for BM to contribute to vasomotor vulnerability in patients with breast cancer. Further studies are needed to elucidate the mechanisms by which BM contributes to CIHF.