Wellness Check: Sleep

2 Minute Medicine is pleased to announce that we are launching Wellness Check, a new series dedicated to exploring new research evidence focused on wellness. Each week, we will report on articles examining different aspects of wellness, including (but not limited to) nutrition, sleep, reproductive health, substance use and mental health. This week, we explore the latest evidence-based updates in sleep. 

Hormonal fluctuations in the menstrual cycle may affect sleep and memory performance

1. In this study, women with regular periods and in the luteal phase of their cycle significantly improved their memory performance overnight in comparison to women taking oral contraceptives and in the follicular phase of their cycle.

2. Women with higher levels of progesterone or progestin had more speed spindles during non-rapid eye-movement stage 2 (NREM2) sleep in comparison to naturally cycling women in their follicular phase, with lower levels of progesterone.

Evidence Rating Level: 2 (Good)

Previous studies suggest sex hormones, such as progesterone, may have a role in memory consolidation during sleep. In particular, changes in sleep spindle activity during non-rapid eye-movement stage 2 (NREM2) sleep have been associated with memory consolidation. Levels of progesterone naturally fluctuate during the menstrual cycle; they are elevated during the luteal phase and decreased in the follicular phase. In contrast, women on oral contraceptives (OC) have low levels of endogenous progesterone but have elevated potent synthetic progestin. The objective of this study was to investigate the effect of progesterone levels in three groups of women (natural cycling women in the luteal phase; naturally cycling women in the follicular phase; women using OCs) on sleep spindle density (during NREM2) and declarative memory consolidation.

This study included women with a regular menstrual cycle or who used OCs. Exclusion criteria included: travelling over 3 time zones within the last 3 months, current or past drug abuse, coffee consumption exceeding 3 units/ days, and diagnosis of a neurological or endocrine disorder. Women participated in a 7-day study period during which study outcomes assessed salivary progesterone levels and sleep spindle density (via polysomnography), as well as declarative memory performance (via a word pair association task pre and post experimental night).

Results showed memory improvement and an increase in density of fast spindles in women in their luteal phase and women using OC, compared to women in the follicular phase. Progesterone levels were highest in naturally cycling women who were in their luteal phase. However, this study was limited by lack of measurement of synthetic progestin levels in women using OCs, and lack of control for dosing of synthetic hormones in the OC group. Nonetheless, this study suggests that cyclical hormone fluctuations may affect memory performance, which could have clinical implications in the future.

Automatic positive airway pressure may be used as alternative therapy amongst bariatric patients with obstructive sleep apnea

1. In this randomized controlled trial, there was no significant difference in adherence between automatic positive airway pressure therapy (APAP) compared to continuous positive airway pressure therapy (CPAP) amongst patients with obstructive sleep apnea (OSA) awaiting bariatric surgery.

2. There was no significant difference in efficacy of treatment or safety profile between CPAP or APAP therapy.

Evidence Rating Level: 1 (Excellent)

Obstructive sleep apnea (OSA) is a condition prevalent amongst the bariatric population characterized by dynamic upper airway obstruction during sleep. Continuous positive airway pressure (CPAP) therapy is an effective treatment, however patients often fail therapy because of discomfort and inability to sleep. Automatic positive airway pressure (APAP) therapy may be better tolerated in certain patients. The objective of this study was to compare adherence to APAP with CPAP therapies amongst obese patients with OSA awaiting bariatric surgery.

In this randomized controlled trial, obese patients with newly diagnosed OSA awaiting bariatric surgery were included. Patients with a diagnosis of severe cardiovascular, respiratory, or neurological disease, as well as central sleep apnea were excluded. Fifty participants were randomized in a 1:1 ratio to either APAP therapy or CPAP therapy. Study outcomes assessed difference in adherence to APAP and CPAP, as well as treatment efficacy, adverse effects, quality of life, and adherence at one month.

In this study, there was a significant difference in compliance to therapy when expressed as a percentage of overall nights therapy was used (96.9% adherence to APAP compared to 86% adherence to CPAP, p = 0.47). However, in terms of percentage of nights with longer than 4 hour use, there was no significant difference in adherence to either therapy.  Furthermore, there was no significant difference in adherence at one month, treatment efficacy, adverse effects, peri-operative complications, or quality of life. This study was limited as it was underpowered in assessing per-operative complications. Furthermore, considering imminent bariatric surgery is an incentive for patients to adhere to OSA therapy, the results of this study may not be extrapolated. Nonetheless, this study suggested there was no difference in adherence to APAP versus CPAP therapy amongst OSA patients awaiting bariatric surgery.

High sleep reactivity may negatively impact the relationship between night shift work and insomnia symptoms

1. Sleep reactivity to stress was a moderator in the association between the number of night shifts and insomnia symptoms amongst participants in safety-sensitive professions (such as physicians).

2. With low to moderate sleep reactivity to stress scores, there was a positive relationship between number of night shifts worked per month and symptoms of insomnia. 

Evidence Rating Level: 2 (Good)

Sleep reactivity to stress is a concept describing the impact of low coping abilities on sleep. Studies have suggested that physicians experiencing higher sleep reactivity to stress are at increased risk of burnout. The objective of this study was to observe if sleep reactivity to stress may act as a moderator in the association between number of night shifts over the period of one month and insomnia.

In this study, an online survey was widely distributed and targeted towards participants in safety-sensitive professions (such as physicians). Participants first answered questions related to socio-demographics, caffeine intake, work experience, and cigarette smoking. Subsequently, participants completed two standardized scales: sleep reactivity to stress was assessed by the Ford Insomnia Response to Stress Test (FIRST) (high FIRST scores indicating high sleep reactivity to stress); symptoms of insomnia and the degree to which it affected daily function was assessed with the Insomnia Severity Index (ISI).

Results showed that sleep reactivity to stress was a significant moderator in the association between number of night shifts worked per month on symptoms of insomnia. Specifically, high sleep reactivity to stress (high FIRST scores) was correlated with poor sleep, despite working a low number of night shifts per month. Furthermore, at low and medium sleep reactivity to stress, there was a significant positive relationship between the number of night shifts worked and insomnia symptoms. Participant demographics such as age, caffeine intake, cigarette use, and work experience did not significantly impact insomnia symptoms. This study was limited by the fact that the survey was internet-based, participants were self-selected, and more women participated than men. Therefore, results may not be extrapolated to the general population. Nonetheless, this study demonstrated a relationship between insomnia, sleep reactivity and number of night shifts worked, which should be addressed in those more vulnerable working in shift work systems.

Image: PD

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