The influence of sexual activity on sleep: A diary study

Aiming to promote overall health and well‐being through sleep, the present studies examine to what extent sexual activity serves as a behavioural mechanism to improve sleep. The relation between sexual activity, i.e., partnered sex and masturbation with or without orgasm, and subjective sleep latency and sleep quality is examined by means of a cross‐sectional and a longitudinal (diary) study. Two hundred fifty‐six male and female participants, mainly students, completed a pre‐test set of questionnaires and, thereafter, a diary during 14 consecutive days. The cross‐sectional study was analysed using analysis of covariance and demonstrated that both men and women perceive partnered sex and masturbation with orgasm to improve sleep latency and sleep quality, while sexual activity without orgasm is perceived to exert negative effects on these sleep parameters, most strongly by men. Accounting for the repeated measurements being nested within participants, the diary data were analysed using multilevel linear modelling (MLM). Separate models for subjective sleep latency and sleep quality were constructed, which included 2076 cases at level 1, nested within 159 participants at level 2. The analyses revealed that only partnered sex with orgasm was associated with a significantly reduced sleep latency (b = −0.08, p < 0.002) and increased sleep quality (b = 0.19, p < 0.046). Sexual activity without orgasm and masturbation with and without orgasm were not associated with changes in sleep. Further, no gender differences emerged. The present studies confirm and significantly substantiate findings indicating that sexual activity and intimacy may improve sleep and overall well‐being in both men and women and serve as a directive for future research.


| INTRODUCTION
Healthy sleep is essential for physical and mental well-being and for the quality of life. Short and disturbed sleep are associated with negative health outcomes, including obesity, hypertension, diabetes mellitus, and mortality (e.g., Anothaisintawee et al., 2015;Itani et al., 2017;Bertisch et al., 2018). Insomnia symptoms, i.e., difficulties initiating or maintaining sleep, constitute an established risk factor for the development of diverse mental disorders, such as depression, anxiety, and posttraumatic stress disorder (Hertenstein et al., 2019), and may aggravate psychopathology and impede recovery (e.g., Belleville et al., 2011;Gee et al., 2019;Ho et al., 2016;Scott et al., 2021).
Further, insomnia symptoms negatively impact quality of life (Lee et al., 2022) and increase the risk for suicidal behaviours (Winsper & Tang, 2014). Research indicates that over 30% of the general population experiences insomnia symptoms and $6% suffers from insomnia disorder (Ohayon, 2002). Considering the large proportion of people affected by poor sleep and its negative effects on health and quality of life, investigations of behaviours and interventions that may improve sleep are paramount.
It is a widely held notion that sexual behaviour, and particularly orgasm, have a positive influence on subsequent sleep. However, only a few studies have aimed to establish the association between sexual activity and sleep (Brisette et al., 1985;Lastella et al., 2019;Pallesen et al., 2020). Brisette et al. (1985) investigated the effects of bedtime sexual activity, in the form of masturbation with and without orgasm, on polysomnographically recorded sleep but did not find differences in sleep latency or sleep duration compared with reading neutral texts.
Recently, three cross-sectional studies examined the perceived influence of sexual behaviour on subjective sleep variables. A large Norwegian population survey found that masturbation and, even more so, sexual activity with a partner (herein referred to as "partnered sex") resulting in orgasm were experienced to exert positive effects on "subjective sleep latency" and "subjective sleep quality" (Pallesen et al., 2020). These effects were significantly stronger in men than in women. Sexual activity without achieving orgasm was reported to have negative effects on both sleep variables. This negative association was stronger in men and diverges from the previous findings of Lastella et al. (2019), who found that sexual activity is perceived to improve subjective sleep latency and sleep quality, independent of whether orgasm occurred. When asked about the perceived influence of partnered sex with orgasm, comparable proportions of men and women reported a positive impact. A survey among U.S. college students on the sleep-promoting properties of sexual activity revealed that intercourse, particularly with orgasm, reportedly increases sleep propensity in both men and women. Although there was no gender difference in experienced somnolence following masturbation, men were more likely to use masturbation to promote sleep (Gallop Jr et al., 2021). Thus, research consistently shows that sexual activity with orgasm positively affects sleep, but several discrepancies have emerged from the scarce literature. Namely, it remains to be ascertained to what extent the type of sexual activity (i.e., partnered sex versus masturbation) impacts the effects on sleep, whether having an orgasm is necessary for such effects to become apparent, and lastly, whether the effect of sexual activity on sleep differs between men and women. Moreover, the subjective effects of sexual behaviour on sleep were evaluated retrospectively and may be influenced by heteronormative expectations as well as recall bias, thereby limiting the validity of earlier findings. The aim of the present study is to investigate the effects of sexual behaviours on sleep more thoroughly by combining a cross-sectional survey based on the previous work by Pallesen et al. (2020) and Lastella et al. (2019) with a longitudinal design in the form of a diary study. Based on the literature, it was hypothesised that sexual activity decreases sleep latency and increases sleep quality. These effects are suggested to be stronger if sexual activity involves a partner, relative to masturbation. Moreover, it is anticipated that this effect is stronger in men than in women, and only detectable if sexual activity resulted in orgasm.

| Participants
A total of 256 participants was recruited using availability sampling. The majority (n = 201) consisted of undergraduate psychology students, who received course credits as compensation for their participation. The remaining participants (n = 55) were randomly recruited by means of social media platforms such as Facebook and LinkedIn. Participants who did not have a stable internet connection (n = 3), were under 18 years of age (n = 1), or had indicated that they were diagnosed with and were currently in treatment for a psychological, sexual, or sleep disorder (n = 14) were excluded. An additional n = 14 participants had to be excluded as they had not given informed consent. The statistical analysis of the crosssectional study was conducted on the remaining sample of 224 participants (67 men, 153 women, 4 other), aged between 18 and 58 years (M = 21.93, SD = 6.46). For analysis of the diary data, participants who had completed less than 50% of the diary (i.e., < 7 days), took antidepressant medication, or indicated the use of hard drugs (i.e., cocaine, mushrooms, MDMA, speed) were excluded (n = 65). Thus, 2076 cases nested within 159 individuals (103 women, 53 men, 3 other, age M = 22.01, SD = 6.52) were analysed. The study was approved by the Ethics Committee of the Behavioral and Social Sciences (ECP: PSY-2021-S-0024).

| Procedure
All participants received the pre-test including the informed consent, as well as the daily diary, via Qualtrics ® (Qualtrics, 2014). If inclusion criteria were met, the participants were asked to enter their email address before the remaining items of the cross-sectional questionnaire were made available to them. Via email, eligible participants received information concerning the study procedure immediately after sign-up.
From the following day on, a daily reminder email including an individualised survey link was sent to every participant at 5 a.m. for 14 days, starting the day after pre-test administration. Thus, the diary was completed once a day upon awakening. Qualtrics generated an individual code for each participant to ensure anonymity, enabling deletion of all email addresses once data collection had come to an end. If inclusion criteria were not met, participants immediately received an email explaining the reason(s) for their exclusion, after which no further emails were scheduled, and no data were stored.

| Cross-sectional study
The cross-sectional study consisted of items assessing gender, age, email address, available internet connection, diagnosis, and current treatment of mental health or sleep disorder or sexual dysfunction, use of hormonal contraception, medication, and habitual alcohol and caffeine consumption. Insomnia was measured using the Insomnia Severity Index (ISI; Morin et al., 2011), a 7-item self-report questionnaire assessing insomnia symptoms during the past two weeks. The items are rated on a 5-point Likert scale ranging from 0 (no problem) to 4 (very severe problem). The total score (0-28) can be interpreted as: ≤7 no insomnia; 8-14 sub-clinical insomnia; ≥15 clinical insomnia (≥22 very severe insomnia).
To enable partial replication of the results appraised by Pallesen et al. (2020), their self-constructed cross-sectional survey (see Appendix S1: Supplement 1) was employed to assess how sexual activity is retrospectively perceived to impact sleep. The survey consists of eight items on the perceived effects of sexual intercourse and masturbationÀ both with and without orgasm À on subsequent sleep latency and sleep quality. Response options ranged from À2 ("much longer than without sex" for sleep latency and "much worse than without sex" for sleep quality) to 2 ("much shorter than without sex" for sleep latency and "much better than without sex" for sleep quality). For an overview of all items of the cross-sectional study, see Appendix S1: Supplement 2.

Sleep
Following the cross-sectional study, participants completed a daily diary assessing sleep and sexual activity for the next 14 days. To assess sleep variables, the Core Consensus Sleep Diary (CCSD; Carney et al., 2012) was utilised. Participants were asked about various aspects of their sleep, including sleep latency and sleep quality. Furthermore, the CCSD was supplemented with items measuring alcohol consumption, the presence of menstruation, and whether unusual events had occurred that might have influenced participants' sleep during the past 24 h.

Sexual activity
Within the same time period, the participants were first asked whether any kind of sexual activity had taken place during the preceding 24 h. If sexual activity had occurred, a 9-item self-constructed sexual activity scale was displayed, assessing how often and at which times of the day, and whether sexual activity had taken place within 2 h of going to sleep. Four items served the appraisal of the type(s) of sexual activity participants had engaged in (masturbation or partnered sex with oral/vaginal/anal sex) and whether an orgasm had occurred. To achieve homogeneity between the cross-sectional and longitudinal study, the items were constructed so that their structure resembled the cross-sectional survey assessing the perceived influence of sexual activity on sleep of Pallesen et al. (2020). If sexual activity had taken place more than once, participants were asked to refer to the last sexual encounter or activity that day. On day 14, additional items were presented assessing the honesty and social desirability of the answers given, the occurrence of life-altering events, and the perceived influence of their study participation on sexual activity and sleep-wake behaviour (for items, see Appendix S1: Supplement 3 and 4).

| Cross-sectional study
To determine whether the perceived effect of sexual activity on sleep differs between men and women, an analysis of covariance (ANCOVA) with ISI total score as covariate was conducted. In line with Pallesen et al. (2020), follow-up analyses consisted of the calculation of weighted means (separately for men and women) with 95% confidence intervals to evaluate whether sexual activity was perceived to improve sleep latency and sleep quality.

| Longitudinal study
Accounting for the time-nested structure of the diary data, analyses were conducted using multilevel linear modelling (MLM; Singer & Willett, 2003). Two models were constructed using SPSS Linear Mixed Models, version 28, to investigate whether partnered sex with orgasm, partnered sex without orgasm, masturbation with orgasm, and masturbation without orgasm prior to sleep possess predictive qualities regarding subjective sleep latency (Model 1) and sleep quality (Model 2). Gender was added as a level 2 predictor, and an interaction effect between gender and partnered sex with orgasm was included to test whether the relationship between sexual activity and sleep is moderated by gender. Outcome variables were checked for multivariate normality, which was violated in sleep latency data. Therefore, subjective sleep latency was log-transformed.
For each outcome variable, a two-level random-intercept model was built. Random intercepts were added to account for random between-subject variance at the mean level of subjective sleep latency and sleep quality. Other predictors were entered as fixed effects. To ensure that differences between models did not result from differences in the covariance structure of the repeated measures factor, models were tested with a diagonal covariance structure (i.e., heterogeneous variances with zero correlations), compound symmetry (i.e., constant variance and covariance), and AR1, which is a first-order autoregressive structure with homogenous variances. The model of best fit according to Akaike's Information Criterion (AIC) values was used. Before adding predictors to the model, the intraclass correlation (i.e., the ratio of variance between individuals to variance within individuals) was calculated to establish whether measurements were significantly clustered within individuals, which justifies the use of MLM instead of aggregating scores and analysing the data on a single level. To analyse whether a model including predictors provides a better fit than the intercept-only model (i.e., a random-intercept model with no predictors) and therefore predicts dependent variables better than chance, the X 2 Likelihood-ratio test of difference was used. Relevant covariates were determined by predicting each outcome variable by alcohol, caffeine, menstruation, insomnia, and contraception. Significant predictors were used as control variables in respective models.

| Cross-sectional study
For the distribution of the answers for each item of the crosssectional study, broken down by gender, see Appendix S1: Supplement 5. When examining the means, it becomes apparent that both partnered sex and masturbation with orgasm resulted in reduced subjective sleep latency and increased subjective sleep quality compared with sexual activity without orgasm or no sexual activity at all. Table 1 presents the means and standard deviations of subjective sleep latency and sleep quality for all levels of sexual activity.
Further, the number of occurrences of sexual activity and masturbation with and without orgasm are displayed and depict differences between men and women. It is noteworthy that, despite women being overrepresented in the present sample (n = 153 women vs. n = 67 men), men reported higher numbers of sexual activities with orgasm than women. negative effect on sleep latency in men (p < 0.001), although women (p < 0.001) also reported prolonged sleep latency (see Table 3).

| Subjective sleep quality
When indicating whether subjective sleep quality changes following partnered sex with orgasm, both men (p < 0.001) and women (p < 0.001) reported an increase in sleep quality (p < 0.097). Further, also without significant differences between genders (p < 0.537), both men (p = 0.039) and women (p < 0.006) perceived partnered sex without orgasm to negatively affect sleep quality. Masturbation with orgasm was found to improve both men's (p < 0.001) and women's (p < 0.001) subjective sleep quality (p < 0.565). Masturbation without orgasm was perceived to have a negative effect on sleep quality in men (p < 0.002) and women (p < 0.001), albeit subjective sleep quality was affected more strongly in men (p < 0.034, see Table 4).  Note: À2 = strong negative effect, 0 = no effect, 2 = strong positive effect. *Significant at α =0.05.

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T A B L E 4 Effects of sexual activity on sleep quality in men and women including weighted means and confidence intervals Note: À 2 = strong negative effect, 0 = no effect, 2 = strong positive effect. *Significant at α = 0.05. gender, and gender was not included in the parsimonious model (see Table 5).

| Subjective sleep quality
The null model with subjective sleep quality as a dependent variable yielded an intraclass correlation of 0.24; therefore, it was considered valuable to proceed with building a multilevel linear model. Alcohol average, report a higher sleep quality than men (see Table 4), no significant interaction effect was found (F 1,1756 = 1.321, p = 0.267).
Thus, no evidence for gender moderating the relationship between partnered sex and subjective sleep quality emerged. Therefore, the final parsimonious model does not include gender as a variable (for an overview of the final Model, see Table 6). masturbation with orgasm did not affect the respective sleep variables. The effects of partnered sex without orgasm and masturbation without orgasm did not have strong enough effects on sleep latency or sleep quality to be detectable in the present design. Although women indicated a higher average sleep quality than men, gender was not found to significantly moderate the relation between sexual activity and sleep.

| DISCUSSION
The present results largely support the hypothesis that sexual activity with orgasm results in reduced subjective sleep latency and increased subjective sleep quality in both men and women. While both studies found significant effects of partnered sex, masturbation though retrospectively perceived as sleep-promotingdid not exert detectable effects in the longitudinal study. As masturbation with orgasm was indeed perceived to effectively promote sleep when assessed in retrospect, the results may suggest that, in fact, both sex with a partner and masturbation impact sleep latency and sleep quality, while the effect of partnered sex may be stronger and thus more salient. This postulate aligns with findings by Brody and Krüger (2006), who have shown that orgasm following sexual intercourse results in a 400% higher post-coital prolactin surge than masturbation-induced orgasm. As prolactin promotes sleep and is part of a feedback loop communicating sexual satiety, the increased postcoital surge of prolactin may explain why partnered sex is often perceived as more satisfying than masturbation and why the sleepfacilitating effect of sexual activity with orgasm is more salient when a partner is involved, as also found by Pallesen et al. (2020) and Gallop et al. (2021).
The finding that both partnered sex and masturbation without orgasm yielded noor even negativeeffects on sleep point to the relevance of orgasm and its concomitant psychophysiological effects.
As orgasm is established to increase the heart rate and blood pressure and results in the release of oxytocin and prolactinhormones, both postulated to influence sleep (Brody & Krüger, 2006;Fekete et al., 2014;Gianotten et al., 2021;Lipschitz et al., 2015) neuroendocrine changes following orgasm may contribute to the reduction in sleep latency and increase in sleep quality following partnered sex with orgasm. The present observations are in accordance with earlier findings by Pallesen et al. (2020). Although Lastella et al. (2019) found that sexual activity is also reported to affect sleep when orgasm is not taken into consideration, the percentage of men and women reporting improved sleep latency and sleep quality increased when specifically asked about sex with orgasm. Further, reported gender differences indicating that perceived effects of sex on sleep are stronger in men were non-apparent when orgasm was assessed and may therefore emanate from a gap in orgasm frequency between men and women.
Therefore, the discrepancy in results may also stem from less nuanced wording of items applied by Lastella et al. (2019). In a more recent study, Sprajcer et al. (2022) found that orgasm frequency explained 3.1% of the variance in subjective sleep latency, as participants reporting an orgasm "every time" sexual activity occurs fell asleep on Abbreviation: σ 2 e = variance at level 1 (repeated measures); σ 2 u = variance at level 2 (individuals).
average 12 min faster than those who less frequently or never report orgasm.
Given that masturbation with orgasm did not produce significant changes in longitudinally assessed sleep, orgasm per se does not sufficiently explain the reduction of sleep latency and increased sleep quality following partnered sex with orgasm. Other factors accompanying partnered sex with orgasm may also contribute to its positive effects on sleep, such as the mere experience of intimacy with one's partner promoting couple bonding (Kruger & Hughes, 2011), wellbeing, and emotion regulation (Gianotten et al., 2021) and may thereby improve sleep. Germane to this, non-sexual touch and cuddling have been shown to have calming, sleep-promoting effects, especially for women (Dueren et al., 2022). Compared with masturbation, partnered sex is often associated with more intense and longerlasting physical activityresulting in a heightened relaxed state afterwardswhich may explain why partnered sex without orgasm resulted in a borderline-significant effect on sleep quality in the diary study despite being reported significantly less frequently than part- This negative perception, although not supported by the longitudinal findings, may be attributed to adjuvant emotions such as frustration, dissatisfaction, uncomfortable bodily sensations resulting from sexual arousal without orgasm, or confounding events that prevented sexual activity from resulting in orgasm.
The hypothesised gender difference suggesting that the effects of sexual activity on sleep are stronger in men than in women was not supported, as changes in subjective sleep latency and sleep quality following partnered sex with orgasm did not differ between men and women. This finding corresponds to results of Kruger and Hughes (2011), who also did not find any gender differences in the influence of sexual activity on sleep, and of Lastella et al. (2019), who did not find a gender difference when sex with orgasm had occurred. The absence of gender differences in the sleep effects of sexual activity with orgasm may be due to comparable endocrine processes following orgasm in men and women (Georgiadis et al., 2009;Mah & Binik, 2002). The widely held notion that men fall asleep faster than women after sexual activity may have emanated from the existing gender gap in achieving orgasm, i.e., women are less likely to reach orgasm during heteronormative sexual activity than men (Blair et al., 2018). Case numbers of the present study corroborate this notion, as although the sample consists of more than twice as many women as men, men reported a higher number of occurrences of both partnered sex and masturbation with orgasm. While following heteronormative scripts, women tend to engage in sexual activities that frequently result in orgasm for men but less often for women (e.g., vaginal penetration only, which does not suffice to achieve orgasm for most women; Lloyd, 2022). Research has further shown that the male orgasm frequently signifies the end of sexual intercourse (Opperman et al., 2014), which decreases the opportunities to achieve an orgasm for women. Women might simply reach orgasm less often and, therefore, less frequently benefit from the sleep-promoting effects of orgasm, which, in turn, may explain why society and cross-sectional research relying on self-report data postulate that men fall asleep faster following sexual intercourse with orgasm.  (1985). Another pathway could be to use a multi-modal machine learning approach implementing wearable devices to detect whether subjective and objective relations of sex and sleep patterns correlate.

| Strengths and implications
As the first to build upon previously conducted cross-sectional studies while also including a longitudinal design, the present study corroborated and extended the evidence for a sleep-promoting effect of sexual activity on sleep. By conducting an analysis in which the data are not aggregated but analysed with respect to their nested structure using MLM, the present study offered the opportunity to clarify diverging results regarding gender differences, type of sexual activity (masturbation vs. partnered sex), and the role of orgasm appraised by prior research. Moreover, controlling for relevant covariates, especially alcohol consumption which appeared to obscure the relationship between sexual activity and sleep, was valuable in the present study and is recommended for future research. The 14-day duration of the diary study, that includes weekdays as well as weekends, demands increased commitment of participants and further increases the value of inferences.
By using a cross-sectional design resembling the study conducted by Pallesen et al. (2020), their main findings could be replicated. The present study shows that both men and women perceive sexual activity followed by orgasm to reduce sleep latency and increase sleep quality (Gallop Jr. et al., 2021;Lastella et al., 2019;Pallesen et al., 2020). The results of the diary study corroborate the finding that sexual activity improves sleep while highlighting the effect partnered sex has on sleep, compared with masturbation. The heightened effect of partnered sex may partly be explained by the increased neuroendocrine changes following intercourse-induced orgasm, in combination with the valuable effects of experiencing intimacy with one's partner. Penetration and sexual intercourse aligned to heteronormative scripts may not necessarily be required to experience the beneficial effects of sexual activity on sleep. This notion is supported by the borderline-significant effect of partnered sex without orgasm on sleep quality, which is frequently reported by women and shows that intimacy alone may be sufficient to experience positive effects on sleep.
The present discordance of results between the cross-sectional study measuring the perception of the effects and the longitudinal study measuring the actual experience underlines the importance of applying objective measures and prospective measures appraising the perceived effect to the concepts of interest, as the subjective experience of sleep was shown to be a strong predictor of physical and mental well-being and cross-sectional methods are prone to be influenced by expectations and norms surrounding sexuality. In general, the same heteronormative implications of sexuality that underlie the orgasm gap between women and men may influence conceptions about "normal" sexualitythereby resulting in confounded popular notions, such as men falling asleep first following sexual intercourse.
Therefore, culture-specific norms and beliefs surrounding sexuality warrant consideration when interpreting the results of subjective research on sexuality.
The outcomes of the present research have important implications for sleep-and sexual medicine, as they highlight the value of considering partnered sex, masturbation, orgasm, and intimacy as a means to promote good sleep. The establishment of a relationship between sexual activity and sleep serves as a directive for future research to identify possible underlying mechanisms, such as endocrine or social-psychological processes, and to attempt an establishment of the effect using objective measures.

| CONCLUSION
As the first to implement both cross-sectional and longitudinal measures to study the effects of sexual activity on sleep, the present study underpins the positive effect of sexual activity on sleep latency and sleep quality. Both studies found sexual activity involving a partner and resulting in orgasm to be perceived as sleep-promoting, while masturbation with orgasm was not found to significantly influence sleep in the longitudinal study. Sexual activity without orgasm was retrospectively reported to negatively affect sleep. While no gender differences in the positive effect of partnered sex with orgasm on sleep emerged, the negative effects of sexual activity without orgasm were stronger in men. The results of the present studies indicate that sexual activity, especially with a partner, may be a valuable behavior to promote good sleep and, thereby, overall health.