Couples who sleep next to one another promote REM sleep

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In many countries, sharing a bed with a partner is common practice. Yet, research investigating the relationship between bed sharing and sleep quality is both scarce and contradictory.

Most studies have compared co-sleep to individual sleep in couples by only measuring body movements. However, Dr. Henning Johannes Drews of the Center for Integrative Psychiatry (ZIP), Germany and colleagues overcame these limitations by also assessing sleep architecture in couples that shared a bed.

Researchers conducted the study among 12 young, healthy, heterosexual couples who spent four nights in the sleep laboratory. They measured sleep parameters both in the presence and absence of the partner using dual simultaneous polysomnography, which is a “very exact, detailed and comprehensive method to capture sleep on many levels — from brain waves to movements, respiration, muscle tension, movements, heart activity” says Dr. Drews.

Additionally, the participants completed questionnaires designed to measure relationship characteristics (e.g., relationship duration, degree of passionate love, relationship depth, etc.)

The results showed that rapid-eye movement (REM) sleep is both increased and less disrupted in couples sleeping together compared to when they slept individually.

This finding is particularly relevant because REM sleep, which is associated with vivid dreams, has been linked to emotion regulation, memory consolidation, social interactions and creative problem solving.

The team also found that couples synchronize their sleep patterns when sleeping together. This synchronization, which is not linked to the fact that partners disturb each other during the night, is positively associated with relationship depth.

In order words, the higher participants rated the significance of their relationship to their life, the stronger the synchronization with their partner.

The researchers propose a positive feedback loop in which sleeping together enhances and stabilizes REM sleep, which in turns improves our social interactions and reduces emotional stress.

Although researchers did not specifically measure these possible effects, Dr. Drews says that “since these are well known effects of REM sleep, it is very likely that they would be observed if testing for them.”

Interestingly, researchers found an increased limb movement in couples who share the bed. However, these movements do not disrupt sleep architecture, which remains unaltered. Dr. Drew states that “one could say that while your body is a bit unrulier when sleeping with somebody, your brain is not.”

Although results are promising, many questions remain to be answered. “The first thing that is important to be assessed in the future is whether the partner-effects we found (promoted REM sleep during co-sleep) are also present in a more diverse sample (e.g., elderly, or if one partner suffers from a disease)” says Dr. Drew.

Despite the small sample size and the explorative nature of some of the analyses, this research furthers our understanding of sleep in couples and its potential implication for mental health. Dr. Drews adds that “sleeping with a partner might actually give you an extra boost regarding your mental health, your memory, and creative problem-solving skills.”


Impact of chronotypes
Morningness–eveningness preferences are seen and understood both as a personality trait and as a trait based on biological factors (Duarte et al., 2014). The trait aspect is especially interesting for human mating behavior. Before couples even get closer together, chronotypes seem to be an important factor in assortative mating.

Two extreme chronotypes with different circadian rhythmicity are unlikely to meet because of their small overlap in their preferred active time. However, low dissimilarity in morningness–eveningness is not linked to higher relationship satisfaction (Randler & Kretz, 2011).

Nevertheless, women would prefer a partner with a similar chronotype. Randler et al. (2014) compared the sleep–wake behavior of women with that of their actual partners and that of a hypothetical, preferred partner.

They could show that, given the choice, females would prefer a partner closer to their own sleep–wake rhythm, indicating that assortative mating according to sleep–wake rhythm may exist.

Among various sleep–wake measures, women particularly prefer a partner going to bed at the same time. It should be noted that these preferences may depend on the phase of a woman’s menstrual cycle.

Chronotypes and gender preferences also have consequences for a couple’s sexual activity. Jankowski et al. (2014) have shown that there is a general major evening peak of sexual activity and desire in females, regardless of their chronotype.

Whereas in males, the greatest need for sex occurred either in the morning or evening hours according to their chronotype (evening types at 9:00–12:00 and 18:00–3:00 and in morning types at 6:00–12:00 and 18:00–24:00).

As a possible consequence, couples with mismatched chronotypes have more marital conflicts and less sexual intercourse than matched couples (Larson et al., 1991).

Chronotype can not only impact the timing of desire and sexual activity, but also the number of sexual partners: In males, eveningness seems to be associated with a higher number of sexual partners and while there was no such correlation found in females, associations between eveningness and behavioral traits that are instrumental in short-term mating strategies are stronger for women than men (Maestripieri, 2014).

One possible explanation for this connection of eveningness and number of sexual partners may be that evening types tend to display higher risk-taking propensities which may be causally or functionally linked to their propensities for sensation- and novelty-seeking, impulsivity, and sexual promiscuity (Ponzi et al., 2014).

Furthermore, gender-specific differences concerning chronotypes can be found in the literature: Girls and women are significantly more morning oriented than boys and men, while men have a more pronounced eveningness preference (Randler, 2007).

These differences could stem from a different interplay between the circadian pacemaker and the sleep–wake cycle processes, which could in turn help to make the circadian system in males more flexible and more able to adapt to environmental change than that in females, whereas the genetically programmed circamensual rhythm in women may contribute to making their circadian systems less flexible and less adaptable to environmental change (Adan & Natale, 2002) (Table 2).

Despite genetic predispositions, chronotypes seem to be able to change and adapt depending on the social circumstances: women are more morning-oriented than men until the age of 30, whereas women older than 45 years are more evening-oriented than men.

The phase-delay of adolescents and the phase-advance of the elderly seem to be more present in men than in women (Duarte et al., 2014). Also social zeitgeber like the scheduling by children and family has a very large impact on a mother’s lifestyle and sleep–wake rhythm, far beyond the first months of life. Children seem to be an even more important social factor than the male partner (Leonhard & Randler, 2009).

Table 2.

Literature on circadian preferences and sleep concordance.

AuthorsYearTitleType of paperMain findingsSample sizePopulation background
Jankowski, Diaz-Morales, & Randler2014Chronotype, gender, and time for sexOriginalChronotype can have an impact on the time of day when humans feel the greatest need for sex and the time of day they actually undertake sexual activity.565 
Maestripieri2014Night owl women are similar to men in their relationship orientation, risk-taking propensities, and cortisol levelsOriginalNight-owl pattern is more prevalent in men than in women, particularly between puberty and menopause. Eveningness may have evolved relatively recently in human evolutionary history and may be advantageous in pursuing short-term mating strategies. Eveningness in males seems to be associated with a higher number of sexual partners, but associations between eveningness and behavioral traits that are instrumental in short-term mating strategies are stronger for women.501Master’s students
Ponzi, Wilson, & Maestripieri2014Eveningness is associated with higher risk-taking, independent of sex and personalityOriginalHigher risk-taking propensities among evening types may be causally or functionally linked to their propensities for sensation- and novelty-seeking, impulsivity, and sexual promiscuity.172 
Fabbian et al.2016Chronotype, gender and general healthReviewAssociations of eveningness with negative outcomes in various domains may be stronger for women that for men.  
Hida et al.2012Individual traits and environmental factors influencing sleep timingOriginalThe sleep timings of a couple are mainly associated with the chronotypes of the husband and wife, but also significantly influenced by certain environmental factors.450Married Japanese couples, living together for >1 year
Gunn, Buysse, Hasler, Begley, & Troxel2015Sleep concordance in couples is associated with relationship characteristicsOriginalWives’ marital satisfaction is associated with couples’ sleep concordance, measured by actigraphy, regardless of husbands’ attachment style (anxious or avoidant).96Heterosexual, healthy, married couples, sharing beds
Hasler & Troxel2010Couples’ nighttime sleep efficiency and concordanceOriginalIn men, higher diary-based sleep efficiency predicted less negative partner interaction the following day. Vice versa for women, less negative partner interaction during the day predicted greater actigraphy-based sleep efficiency that night.58Heterosexual couples, sharing beds
Meadows et al.2009Exploring the interdependence of couples’ rest–wake cyclesOriginalThe variables of sleep most significantly interdependent in couples are actual bed time, sleep latency, light/dark ratio and wake bouts.72Heterosexual couples
Randler & Kretz2011Assortative mating in morningness–eveningnessOriginalTwo extreme chronotypes are unlikely to meet each other because they have the smallest overlap in their preferred active time during the day due to the circadian rhythmicity.96Heterosexual couples
Randler et al.2014Women would like their partners to be more synchronized with them in their sleep–wake rhythmOriginalAssortative mating according to sleep–wake rhythm exists, but for long-term pair-bonds, women would like their partners more synchronized.167Women

Finally, when considering gender as a moderating variable, according to a recent review of the literature by Fabbian et al. (2016), associations of eveningness with a number of negative outcomes in the domains of physical and psychological health, sleep and achievement may be stronger for women than for men.

Effect on relationships
Sleep problems and relationship problems tend to co-occur, particularly during times of significant life events or transitions, such as adjustment to an illness, the birth of the first child, or relationship dissolution (Troxel, 2010).

Thus, the link between sleep and relationship quality is supposed to be bidirectional, reciprocal and dynamic. The model of dynamic association between relationship functioning and sleep by Troxel et al. (2007) is based on reciprocal pathways and gives a possible theoretical framework of the interplay between sleep and relationship quality.

In a healthy relationship, a partner serves as a successful stress-buffer by providing downregulating physiological and psychological stress responses and counteracting health behaviors that could have a negative impact on sleep.

In contrast, stressful relationships lead to increased physiological and emotional arousal, poor health behaviors, and a greater risk for sleep disturbance and disorders. Empirically there seem to exist some gender differences: for females, less negative partner interaction during the day predicted greater sleep efficiency in the following night, whereas vice versa for males, higher sleep efficiency predicted less negative partner interaction the following day (Hasler & Troxel, 2010).

Similarly, wives’ marital satisfaction is associated with couples’ sleep concordance measured by actigraphy, regardless of husbands’ attachment style (anxious or avoidant) (Gunn et al., 2015). The variables with the most significant couple interdependency are: timing of going to bed, sleep latency, light/dark ratio, and wake bouts (Meadows et al., 2009).

Over time, couples evolve interactional rules and sleep routines that bind them together. These behaviors need some time to emerge in a new relationship and often imply a modification of sleep behavior (Hislop, 2007).

Couple sleeping and sleeping disorders
Most of the literature about couple sleeping does not deal with this subject as a daily phenomenon but within a clinical context with regard to sleep disorders. Females sleeping with male snorers have decreased sleep quality and increased sleep fragmentation.

However, it cannot be suggested that objective sleep quality improves substantially in the female non-snoring partner when she sleeps alone for one night (Blumen et al., 2009). In a study conducted by Ulfberg et al. (2000) spouses of snorers also more frequently report sleeping problems, insomnia, daytime fatigue and sleepiness.

No differences were found between spouses of snorers who sleep in the same room and those who sleep in separate rooms. Wives of patients suffering from obstructive sleep apnea (OSA) perceive their marriages as more stressful, and they perceive no regeneration by social activities and leisure time.

Therefore, wives should be integrated in the treatment of their husbands suffering from sleep apnea (Cartwright & Knight, 1987). Patients suffering from OSA can improve their quality of life through continuous positive airway pressure (CPAP). Parish and Lyng (2003) showed that the use of CPAP also improves the quality of life in their sleeping partners in the domains of role-physical, vitality, social functioning, role-emotional and mental health. Moreover, wives can even have a supportive effect on the use of CPAP.

In a study by Cartwright (2008), treatment adherence was strongly related to the wife sharing the bed. After 2 weeks of CPAP, men’s score on the Sleep Apnea Quality of Life index improved and was significantly higher than the wife’s score, indicating that the man was better adjusted to his diagnosis and treatment than she was.

Husbands who slept separately used their CPAP machine less frequently than regular bed sharers. Furthermore, the sleep of the non-sharing wives was negatively impacted by their partners’ CPAP use.

Previous findings indicate that relationship quality plays an important role when diagnosing sleep disorders and that it may lead to important information concerning the etiology and maintenance of the disorder. Furthermore, a healthy relationship and a motivating co-sleeper may be an important motivating factor to initiate and adhere to treatment.

Conversely, if relationship problems are presumed to be a significant factor in the etiology or maintenance of a sleep disorder, couples’ counseling may be an important adjunct to treatment (Troxel et al., 2007).

Couple sleeping and mental health
Recent research indicates that there are some connections between couple sleep and mental health. El-Sheikh et al. (2013) investigated a possible intervening effect of mental health variables on interpartner psychological conflict and couple sleep in 135 couples.

The authors showed that depression and anxiety symptoms functioned as intervening variables and affected both the own and the partner’s sleep. Women being the recipient of interpartner psychological conflict had more symptoms of anxiety, which was associated with reduced sleep efficiency.

Results also indicate depression symptoms to be an intervening variable in the association of being recipient of interpartner psychological conflict and sleep quality. Also the perpetration of interpartner psychological conflict was found to be related to increased anxiety within the partner, which was related to longer sleep latencies for the actor.

Revenson et al. (2016) investigated associations between anxiety and depression symptoms and couple sleep in a sample of 543 middle-aged couples. Results indicate that high levels of anxiety and depression had an influence on the partner’s sleep duration.

The effect of the men’s mental health on their wives was stronger than vice versa, for example women with husbands showing high levels of depression had a shorter sleep duration one year later, while the reverse effect from husbands’ depression symptoms on their wives’ sleep duration was not significant.

Also a small moderating effect of sleep duration was found in the sample: in women with shorter sleep duration, depressive symptoms were more strongly related to depressive symptoms one year later than in those with longer sleep duration. Troxel et al. (2007) examined the relationship between attachment anxiety, marital status, bed-partner status, and sleep in 107 women suffering from recurring major depression.

Relationship measures had no main effect or interactional effect on subjective sleep quality, but a polysomnography indicated that women with a bed partner had better sleep efficiency. Married women showed shorter sleep latencies compared to never married women.

A reduced percentage of stage 3 and 4 sleep was found in anxiously attached women. In addition, a significant interaction was found between attachment anxiety and marital status: anxiously attached women who were divorced, separated or widowed displayed a particularly low percentage of stage 3 and 4 sleep.

Overall results indicate that depressed women are a high-risk group vulnerable to psychological and physical health threats. Past and current relationship experiences seem to have important implications for present sleep.

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