Two studies of menstrual synchrony: negative results

Physiological and pharmacological perspectives of melatonin

The pineal gland is a interface between light-dark cycle and shows neuro-endocrine functions. Melatonin is the primary hormone of pineal gland, secreted at night. The night-time melatonin peak regulates the physiological functions at dark. Melatonin has several unique features as it synchronises internal rhythm with daily and seasonal variations, regulates circadian rhythm and sleep-wake cycle. Physiologically melatonin involves in detoxification of free radicals, immune functions, neuro-protection, oncostatic effects, cardiovascular functions, reproduction, and foetal development. The precise functions of melatonin are exhibited by specific receptors. In relation to pathophysiology, impaired melatonin secretion promotes sleep disorder, cancer progression, type-2 diabetes, and neurodegenerative diseases. Several reports have highlighted the therapeutic benefits of melatonin specially related to cancer protection, sleep disorder, psychiatric disorders, and jet lag problems. This review will touch the most of the area of melatonin-oriented health impacts and its therapeutic aspects.

On the Communicative Function of Body Odors

Humans use multiple senses to navigate the social world, and the sense of smell is arguably the most underestimated one. An intriguing aspect of the sense of smell is its social communicative function. Research has shown that human odors convey information about a range of states (e.g., emotions, sickness) and traits (e.g., individuality, gender). Yet, what underlies the communicability of these states and traits via smell? We fill this explanatory gap with a framework that highlights the dynamic and flexible aspects of human olfactory communication. In particular, we explain how chemical profiles, associative learning (i.e., the systematic co-occurrence of chemical profiles with state- or trait-related information), and top-down contextual influences could interact to shape human odor perception. Our model not only helps to integrate past research on human olfactory communication but it also opens new avenues for future research on this fascinating, yet to date poorly understood, field.

Women Living Together Have a Higher Frequency of Menstrual Migraine

BACKGROUND

Menstrual migraine is a highly prevalent disorder among adult women, resulting in disability and loss of quality of life. Some studies have reported menstrual cycle synchrony among women living together. No study has reported whether there may also be a higher prevalence of menstrual migraine among these women. Thus, they reported here the prevalence of menstrual migraine in a group of women living together compared with a control group of women living alone, and discussed the possible factors involved.

METHODS

The study was conducted on female university students aged 18-30 years with a diagnosis of migraine according to the criteria of the International Classification of Headache Disorders III, beta appendix criteria. The subjects were divided into a group of women who lived together with two or more other students and a control group of age-matched students who lived alone, interviewed with a specific questionnaire and assessed for 3 months by means of a paper pain diary. The data evaluated included frequency of headache, presence of menstrual migraine, intensity of headache, medications used including contraceptives, and triggering factors such as diet, sleep deprivation, and stress. The menstrual data and data related to migraine were also investigated in the roommates.

RESULTS

A higher occurrence of menstrual migraine among women living together (9, 50%) compared with women living alone (3, 16.7%) (P = .03) was detected. After binary logistic regression analysis, this finding was not related to the main influencing factors detected, that is, use of a contraceptive, test stress, or sleep deprivation (P = .03, adjusted odds ratio: 7.87; 1.23-50.36). These women also showed menstrual cycle synchrony with their roommates (8, 44.4%) and the presence of headache crises during the menstruation of their colleagues (11, 61.1%).

CONCLUSION

The present study detected a higher occurrence of menstrual migraine among women who lived together. Since there was no previous description of this topic in the literature, it was believed that the present study could represent a step toward more elaborate investigations of this complex topic.

Possible evolutionary origins of human female sexual fluidity

I propose an evolutionary theory of human female sexual fluidity and argue that women may have been evolutionarily designed to be sexually fluid in order to allow them to have sex with their cowives in polygynous marriage and thus reduce conflict and tension inherent in such marriage. In addition to providing an extensive definition and operationalization of the concept of sexual fluidity and specifying its ultimate function for women, the proposed theory can potentially solve several theoretical and empirical puzzles in evolutionary psychology and sex research. Analyses of the National Longitudinal Study of Adolescent Health (Add Health) confirm the theory's predictions that: (i) women (but not men) who experience increased levels of sexual fluidity have a larger number of children (suggesting that female sexual fluidity, if heritable, may be evolutionarily selected); (ii) women (but not men) who experience marriage or parenthood early in adult life subsequently experience increased levels of sexual fluidity; and (iii) sexual fluidity is significantly positively correlated with known markers of unrestricted sexual orientation among women whereas it is significantly negatively correlated with such markers among men.

Always follow your nose: the functional significance of social chemosignals in human reproduction and survival

This article is part of a Special Issue "Chemosignals and Reproduction" Across phyla, chemosensory communication is crucial for mediating a variety of social behaviors, which form the basis for ontogenetic and phylogenetic survival. In the present paper, evidence on chemosensory communication in humans, with special reference to reproduction and survival, will be presented. First, the impact of chemosignals on human reproduction will be reviewed. Work will be presented, showing how chemosensory signals are involved in mate choice and partnership formation by communicating attractiveness and facilitating a partner selection, which is of evolutionary advantage, and furthermore providing information about the level of sexual hormones. In addition to direct effects on phylogenetic survival, chemosignals indirectly aid reproductive success by fostering harm protection. Results will be presented, showing that chemosensory communication aids the emotional bond between mother and child, which in turn motivates parental caretaking and protection, leading to infant survival. Moreover, the likelihood of group survival can be increased through the use of stress-related chemosignals. Stress-related chemosignals induce a stress-related physiology in the perceiver, thereby priming a fight-flight-response, which is necessary for an optimum adaption to environmental harm. Finally, effects of sexual orientation on chemosensory communication will be discussed in terms of their putative role in stabilizing social groups, which might indirectly provide harm protection and foster survival. An integrative model of the presented data will be introduced. In conclusion, an outlook, focusing on the involvement of chemosensory communication in human social behavior and illustrating a novel approach to the significance of chemosensory signals in human survival, will be given.

Do non-human primates synchronise their menstrual cycles? A test in mandrills

The concept of female cycle (or estrous) synchrony has enduring popular appeal. However, critical reviews of estrous synchrony studies in both humans and non-humans have found that synchrony has not been demonstrated convincingly, due to methodological artifacts and statistical problems. Studies of this phenomenon in animals living under naturalistic conditions are rare. We used long-term records of the timing of the female menstrual cycle in a semi-free-ranging population of mandrills, together with a randomisation procedure, to test hypotheses relating to cycle synchrony in a naturally reproducing primate. We found evidence of significant synchrony of the peri-ovulatory period in only one of 10 group-years - the year in which the largest number of cycles was recorded, both overall and per female. However, this result was no longer significant when we corrected for multiple tests of the same hypothesis. This suggests that mandrills in our study population do not synchronise their cycles, possibly because they usually conceive so quickly that they do not have the opportunity to synchronise. We also tested whether females in the same matriline, which associate with one another more than other females, cycle significantly more closely together in time than unrelated females, finding that they did so in 2 of 10 group-years, but that they were significantly less likely to match their cycles in another group-year. Across 32 matriline-years, patterns of synchrony within individual matrilines (female lineages) never fell outside the distribution based on chance. Thus we found little support for the pheromonal hypothesis for cycle synchrony, which predicts that females that associate with one another should be more likely to cycle together. Overall, our findings are in line with other studies that suggest that cycle synchrony does not occur in non-human primates.

Physiology and Endocrinology of the Ovarian Cycle in Macaques

Macaques provide excellent models for preclinical testing and safety assessment of female reproductive toxicants. Currently, cynomolgus monkeys are the predominant species for (reproductive) toxicity testing. Marmosets and rhesus monkeys are being used occasionally. The authors provide a brief review on physiology and endocrinology of the cynomolgus monkey ovarian cycle, practical guidance on assessment and monitoring of ovarian cyclicity, and new data on effects of social housing on ovarian cyclicity in toxicological studies. In macaques, cycle monitoring is achieved using daily vaginal smears for menstruation combined with cycle-timed frequent sampling for steroid and peptide hormone analysis. Owing to requirements of frequent and timed blood sampling, it is not recommended to incorporate these special evaluations into a general toxicity study design. Marmosets lack external signs of ovarian cyclicity, and cycle monitoring is done by regular determinations of progesterone. Cynomolgus and marmoset monkeys do not exhibit seasonal variations in ovarian activity, whereas such annual rhythm is pronounced in rhesus monkeys. Studies on pair- and group-housed cynomolgus monkeys revealed transient alterations in the duration and endocrinology of the ovarian cycle followed by return to normal cyclicity after approximately six months. This effect is avoided if the animals had contact with each other prior to mingling. These experiments also demonstrated that synchronization of ovarian cycles did not occur.

Methods for obtaining menstrual-cycle data in menstrual-synchrony studies: commentary on Schank (2001)

J. C. Schank (2001) claimed to identify 2 categories of error-measurement error and recall biases-in the methodology used in studies of menstrual synchrony. This commentary focuses on the 2nd of these, recall biases, and other errors that he argued may result from "allowing participants to fill out menstrual-cycle-onset calendars" (p. 3). J. C. Schank's detailed discussion of various types of recall biases is inappropriate and misleading given that the majority of menstrual-synchrony studies have used prospective menstrual calendars. The use of menstrual calendars is a well-accepted method in a number of research areas and demands little of participants. J. C. Schank questioned the validity of menstrual calendar data on the basis of assumptions about recall bias for which he had no evidence.

Menstrual synchrony and cycle variability: a reply to Schank (2000)

Menstrual synchrony has been measured by a change over time, to capture the "process" of synchronization or by examining a sample of women who have been together for a number of months ("state" synchrony). We have proposed and used a method for calculating "state" synchrony. On the basis of the results of a computer simulation, Schank (Schank, J.C., 2000. Menstrual-cycle variability and measurement: further cause for doubt. Psychoneuroendocrinology 25, 837-847) argues that our method is biased towards finding synchrony and that the degree of error is an increasing function of cycle variability. We show that Schank's model is based on unfounded assumptions. Contrary to Schank's assertion, on which much of the critique is based, there is no evidence that cycle variability is actually large in samples with "state" synchrony. Our reports are valid; and our method is supported both by convergent validity and by the use of statistical "random control" groups.

Measurement and cycle variability: reexamining the case for ovarian-cycle synchrony in primates

Critical reviews of menstrual synchrony studies, over the last 15 years, strongly suggest that synchrony may be a methodological artifact. The primary focus of this paper is on reexamining the evidence for synchrony in the two other primate species: chimpanzees (Pan troglodytes) and golden lion tamarins (Leontopithecus rosalia). It is demonstrated, with computer simulation, that cycle variability can yield misleading measurements of synchrony when it is assumed that the mean absolute difference between points in cycles (e.g. menses onsets, onset of anogenital swelling, peak estrogen levels) is 14 the mean cycle length. This together with inappropriate statistical analyses can lead to the spurious detection of synchrony. In addition, computer simulations indicate that the null hypothesis (i.e. that females do not synchronize their cycles) should not have been rejected in either of these studies. These errors suggest that synchrony in non-human primates is also a methodological artifact. I conclude by suggesting that: (i) from the perspective of female mate choice, synchrony is likely a state to be avoided; and (ii) we must be especially vigilant of studies reporting the discovery of mechanisms of synchrony.

Menstrual-cycle synchrony: problems and new directions for research

Since M. K. McClintock (1971) published the 1st study on menstrual synchrony among women, a number of other studies have also reported synchrony using a variety of methods. The most recent reports of synchrony come from A. Weller, L. Weller, and colleagues, and their findings of synchrony have been getting stronger (by their own account). In this article, the author analyzes their new methodology and presents 2 simulation studies that demonstrate how biases and errors can produce synchrony as an artifact. Two mutually reinforcing categories of errors are identified: (a) errors in calculating the expected mean onset difference between cycles when there is cycle variability and (b) errors that may result from allowing participants to fill out menstrual-cycle-onset calendars, including recall biases and the mutual exchange of information. It is suggested that synchrony may be a biological state to be avoided and that cycle variability may facilitate female mate choice.

Do Norway rats (Rattus norvegicus) synchronize their estrous cycles?

Estrous synchrony was tested using 10 pairs of sibling female rats (Rattus norvegicus). A Monte Carlo bootstrap simulation was used to construct random control groups to avoid previous statistical errors and to test for significance when there are irregular cycles. The 10 pairs of females did not exhibit estrous synchrony. The effect of cycle irregularity on the limits of synchrony was analyzed using an equation that the related degree of cycle regularity to the degree of synchrony. This equation significantly predicted the limits of synchrony: cycle irregularity limits both the maximum and minimum degree of synchrony that can occur between two females. Finally, simulations of the expected levels of synchrony in groups of five rats were compared to the original study on estrous synchrony. The simulations indicated that the results of the original study were consistent with chance levels of synchrony. It is concluded that there is no evidence that Norway rats synchronize their estrous cycles. Evolutionary implications are discussed.

Menstrual-cycle variability and measurement: further cause for doubt

This paper critically examines Weller and Weller's preferred last month only method for measuring synchrony. Within-woman and between-women menstrual-cycle variability are distinguished. If there is within-woman cycle variability, synchrony requires a process of entrainment. Between-women cycle variability precludes synchrony between rhythms that are not integer multiples of each other. The assumptions of Weller and Weller's last month only measurement model are tested by computer simulation under conditions of cycle variability. It is demonstrated that these assumptions are biased towards finding synchrony when it does not exist and that the degree of error is an increasing function of cycle variability. Indeed, the error uncovered quantitatively predicts the peculiar skew in their data distributions. Synchrony is almost impossible when there is cycle variability and finding synchrony may be an indicator of a methodological artifact rather than a phenomenon.

Prolonged and very intensive contact may not be conductive to menstrual synchrony

Menstrual synchrony was not found for 30 cohabiting lesbian couples (mean time living together, 35 months), for whom 3 months of menstrual data were collected prospectively. A combined analysis with two previous studies of lesbian couples (Trevathan, W, Burleson, NH, Gregory, L (1993) No evidence for menstrual synchrony in lesbian couples. Psychoneuroendocrinology 18, 425-431; Weller, A, Weller, L (1992) Menstrual synchrony in female couples. Psychoneuroendocrinology 17, 171-177) also failed to reveal synchrony. These data are considered together with a previous study of Bedouin couples which found only a moderate degree of synchrony (Weller, A, Weller, L (1997a) Menstrual synchrony under optimal conditions: Bedouin families. J Comp Psychol 111, 143-151). When women live together for an extensive period of time and have intensive social contact among them, the intensive contact may not be conducive to menstrual synchrony.

Menstrual variability and the measurement of menstrual synchrony

While the timing of menstrual cycles must be modifiable in order for the phenomenon of menstrual synchrony to occur, cycle variability and the occurrence of irregularly long or short cycles complicate the measurement of the process of synchronization over time and of determining whether synchrony exists for women who have lived together for a long period of time. The paper examines how each of five different ways of measuring menstrual synchrony (utilized in the literature) deals with menstrual variability and irregular cycles. On the basis of this analysis, the mathematical concept of "the limit of a sequence,' and analysis of data according to these five different approaches, we recommend the approach in which women record their onset dates after they have been together for a prolonged period of time. The observed onset differences between the women are then compared to expected onset differences, based on the assumption of random onset occurrence. A significant influence of irregular cycle lengths on synchrony was not found in this data set and in the other studies which examined this issue. Research to date has focused on a relatively narrow aspect of menstrual regularity and synchrony and has failed to emphasize the coupled pattern of events over time as well as to analyze menstrual synchrony as a cyclic system.

When is a butterfly like an elephant?

The behaviours of organisms as diverse as elephants and butterflies are affected by pheromones with identical or similar structures. Recent developments in the molecular biology of pheromone detection suggest why.

Menstrual synchrony: only in roommates who are close friends?

This study examined menstrual synchrony among roommates residing in 20 university housing units. Menstrual synchrony was examined for roommates who were close friends and roommates who were not close friends, and by housing unit. The impact of personality, social-interaction and menstrual-related factors was also studied. To avoid limitations found in previous studies, (i) data were collected prospectively and (ii) over the entire academic year; (iii) high participation rate was obtained (86%); and (iv) women who used oral contraceptives were excluded. Menstrual synchrony was found among roommates who were close friends. Synchrony was not found for roommates who were not close friends, nor by housing units. The phenomenon of menstrual synchrony may more likely occur among close friends and women with intensive social contact than under the conditions common to university dormitories.

Menstrual synchrony: agenda for future research

While many studies have confirmed McClintock's (1971) finding of human menstrual synchrony, it is also clear that menstrual synchrony does not always occur. To better understand the mechanisms and functions of this phenomenon, this paper suggests directions for future research aimed at delineating the context and conditions under which menstrual synchrony occurs. It is proposed that the following research issues be explored: multiple sources of social influence; quality of social relationships; analyzing couple (or group) data; who synchronizes to whom?; group size; putative pheromones; age and age diversity; and contraceptive practices.

The impact of social interaction factors on menstrual synchrony in the workplace

The two objectives of this study were: (1) to examine the impact of social interaction variables (e.g., friendship, time working together, and activity) on the occurrence of menstrual synchrony; (2) to examine the menstrual synchrony of women who work together in an office. The sample consisted of 72 women soldiers in two army bases, and a civilian sample of 36 office workers. None of the samples showed significant synchrony. However, social interaction variables were found to be important factors contributing to the relative degree of synchrony. Friendship, mutual activity, and length of time working together were significantly related to the degree of synchrony.

Heterosexual activity: relationship with ovarian function

Previous research demonstrated a relationship between the temporal pattern of heterosexual activity and an index of ovarian functioning. In the current study, this relationship was investigated in 147 menstruating heterosexual women (aged 19-53). They kept prospective daily records of menses, basal body temperature, sexual activity, and other behaviors for three consecutive menstrual cycles. In contrast to previous findings, women with intermediate levels of sexual activity displayed more frequent optimal menstrual cycles. Pheromones, semen absorption, and orgasm-related changes were tested as mediators for a causal influence of sexual activity on ovarian functioning; none was supported. Exploratory analyses tested the hypothesis that anovulatory cycles (with presumably lower progesterone) would display more sexual activity than ovulatory cycles. This hypothesis was supported, and the difference in sexual activity was limited to the second half of the cycle, after ovulation would have occurred. Thus, the findings incorporate temporal precedence of ovulation to support the idea that physiological processes influence the level of sexual activity in heterosexual women.

Examination of menstrual synchrony among women basketball players

Based on the hypothesis that olfactory communication may underlie menstrual synchrony, we examined menstrual synchrony among eight professional basketball teams in the Israeli womens' major basketball league. We investigated whether team synchrony occurred, whether best friends among the teammates synchronized, and whether menstrual-related or social-interaction factors were associated with synchrony. Synchrony was not found among the teams nor among best friends. No meaningful relation was found between synchrony and menstrual-related or social-interaction variables.

Human menstrual synchrony: a critical assessment/

This review on menstrual synchrony in human females has four purposes: (a) to determine whether or not the phenomenon exists, and whether it differs in the various groups studied: roommates in dormitories, roommates in private residences, close friends, work groups, mothers-daughters; (b) to assess the magnitude of its effect, i.e., to what extent does the single factor of living together affect menstrual synchrony?; (c) to examine the effects of menstrual-related factors, social interaction factors, and personality on menstrual synchrony; (d) to assess whether the findings support a pheromonal or common environmental explanation of menstrual synchrony. Several methodological issues are also discussed.

No evidence for menstrual synchrony in lesbian couples

Menstrual synchrony was investigated in a sample of 29 cohabiting lesbian couples, ranging in age from 22 to 48 years. One or both partners kept prospective daily records of variables including menses onset dates, intimate contact, and sexual activity. All women reported daily intimate interaction with their partners; none reported intimate interaction with men. Despite these potentially optimal conditions for the manifestation of synchrony, the differences between dyad members in menses onset dates were distributed randomly, and there was no evidence of convergence. In fact, most dyads exhibited divergence of onset dates. Reasons for lack of synchrony in this sample are discussed; one conclusion is that there is no solid evidence that menstrual synchrony is a stable attribute of past or contemporary human populations.