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."