Menstrual cycle-related variation in autonomic nervous system functioning in women in the early menopausal transition with and without insomnia disorder

Insomnia is considered a hyperarousal disorder, in which several psychophysiological domains including the autonomic nervous system (ANS) are over-activated, potentially contributing to increased risk for cardiovascular (CV) disease. Here, we aimed to determine whether insomnia that develops in the context of the transition to menopause (menopausal transition insomnia, MTI) is similarly characterized by autonomic arousal. We also took into account modulation of the ANS by the hormonal changes of the menstrual cycle, a factor that has not previously been considered in studies on insomnia. Twenty one women with insomnia (49.0 ± 3 y) and 25 controls (48.8 ± 2.6 y), also in the menopausal transition, had overnight laboratory-based polysomnographic recordings, including electrocardiograph, during the follicular and/or luteal (progesterone ≥ 3 ng ml−1) phases of the menstrual cycle, with 21 women having recordings in both phases. Nocturnal time and frequency-domain heart rate variability (HRV) measures were calculated. Heart rate (HR) was significantly elevated (by ∼4 bpm) in MTI compared to controls in both follicular and luteal phases, across hours of the night, including during undisturbed periods of NREM and REM sleep (p < 0.05). A higher HR tended to be associated with lower frequency- and time-domain vagal HRV indices in MTI compared with controls. In both groups, HR was significantly higher and total and high frequency HRV measures were lower in the luteal phase compared to the follicular phase (p < 0.05). In addition, REM compared to NREM sleep was characterized by increased HR coupled with decreased vagal modulation and increased sympathovagal balance (p < 0.01). Insomnia in the menopausal transition is characterized by nocturnal autonomic hyperarousal during both follicular and luteal phases of the menstrual cycle, which could be a factor in the etiology of MTI as well as a potential CV risk factor.