Lunar influences on the reproductive cycle in women.

Several exogenous influences on the human female's menstrual cycle length have recently been demonstrated. Previously, sexual behavior and pheromonal influences have been described. This report evaluates lunar cyclicity patterns. A relationship is demonstrated between the onset of menstruation, among women who have 29.5 ±1 day menstrual cycles, and the onset of full moon. Four separate prospectively gathered sets of data are presented from different years and seasons. It is demonstrated that these women tend to menstruate in the full of the moon with a diminishing likelihood of menses onset as distance from full moon increases. The length of a woman's menstrual cycle has long been known to bear some reflection of the underlying endocrine milieu as well as her potential for fertility. Vollman et al (1968, 1970, 1977) as well as Treloar et al. (1967, 1981), through their extensive prospective studies, have clearly shown that women whose cycles approach the 29.5 day span have the highest likelihood of fertile cycles, while women whose cycles become longer or shorter have a proportionately diminishing incidence of fertile cycles. About 28% of reproductively mature women show a 29.5±1 day cycle length (Vollman 1968, 1970, 1977). That the most fertile reproductive cycle has the same length as the lunar cycle, i.e. 29.5 days, is an intriguing biological coincidence. In 1979, we reported that although previous investigators had failed to find a relationship between menses onset and the lunar cycle, their failure derived from the inappropriateness of the methods employed. By selecting the subpopulation of wornen (approximately 30%) who cycle as often as the moon does, i.e. 29.5±1 day, a significant pattern was revealed. There was an increased likelihood of men1Athena Institute for Women's Wellness Research, 30 Coopertown Road, Haverford, PA 19041. 2Monell Chemical Senses Center, 3500 Market Street, Philadelphia, PA 19104. 3Osterreichische Academie der Wissenschaften, Institut fur Vergleichends Verhaltensforchung, Vienna. 4School of Science, Department of Health Science, Brooklyn College of CUNY, Brooklyn, New York. 5Department of Obstetrics and Gynecology, University of Pennsylvania, Hospital of the University of Pennsylvania, Philadelphia, PA 19104. 6University of Pennsylvania, Statistics Department, Wharton School, Philadelphia, PA. Human Biology, December 1987, Vol. 59, No. 6, pp. 959-972. © Wayne State University Press, 1987 This content downloaded from 207.46. 13.102 on Sun, 31 Jul 2016 05:06:22 UTC All use subject to http://about.jstor. org/terms 960 / WINNIFRED B. CUTLER ET AL. struation onset in the light half of the lunar month. Thus, in a selected population of 312 women, prospective menstrual cycle records maintained during the Autumn of 1977 showed that 69% of the subsample whose menstrual length was 29.5 ±1 day showed menses onset within 7.5 days of the full moon (Cutler 1980a). A year later, Friedmann (1981) replicated this phenomenon, reporting that 65% of a similarly sized population menstruated in the light half of the lunar cycle. In her sample, the split was optimized with a 3 day lag period after the quarter; i.e. the month was bisected 3 days after the first and third quarter. In this report, we re-evaluate those data using a more sophisticated analytic method and we add data from prospective records collected during 2 other experiments. We hypothesize that a systematic relationship between day of the lunar cycle and density of menses onsets might exist. We also explore whether the season can influence these lunar, menstrual associations. More recently, exogenous influences on menstrual cycle length and other reproductive endocrine patterns have been reported (Cutler et al. 1979a, b,c, 1980, 1983, 1985, 1986; McFalls 1973; McCoy et al. 1985). For example, women who engage in regular weekly heterosexual intercourse tend to have significantly more 29. 5 ±3 day cycles, higher incidences of fertile patterns of basal body temperature graphs, and higher levels of circulating estrogen in both the reproductive and the climateric years than women who have either celibate or sporadic patterns of sexual behavior (Cutler et al. 1979a, b, 1980b, 1983, 1985, 1986a; McCoy et al. 1985). Through analyses of data trends, the direction of causality was considered to be behaviorally manipulable (Cutler et al. 1985, 1986); regular weekly behavior appears sufficient to create 29.5±3 day cycles. Investigations into the underlying mechansisms by which sexual behavior may affect the neuroendocrine rhythm of women has yielded evidence for a pheromonal influence (McClintock 1983, 1984; Cutler et al. 1984, 1986; Preti et al. 1986). Studies in our laboratories employing extracts of axillary secretions from donor men and donor women were shown to significantly alter the timing and length of menstrual cycles of nulliparous women in a double-blind, placebocontrolled study (Cutler et al. 1986; Preti et al. 1986, 1987). Consequently, there appear to be several exogenous influences which promote lunar type cycle lengths in women. Materials and Methods Collection of Menstrual Data« Calendars designed for convenient recording of menstrual and sexual events were employed in four subsequent studies (Cutler 1979a, b). Each calendar contained 4 or 5 months of dated slots for individual This content downloaded from 207.46. 13.102 on Sun, 31 Jul 2016 05:06:22 UTC All use subject to http://about.jstor. org/terms Lunar Influences on the Reproductive Cycle in Women / 961 days and was designed to fit within a wallet. Subjects prospectively gathered data for approximately 14 weeks. Details of the prospective double-blind methods of data collection are described elsewhere (Cutler 1979a). Briefly, subjects were told that they were participating in a study to increase our understanding about reproductive physiology of the menstrual cycle. Sample and Analysis of Menstrual Calendars. Table 1 indicates the number of women for whom menses data were collected in each sample, as well as the percentage of that sample who showed a 29.5 ± 1 day cycle. Of all subjects, 27% had 29.5 ±1 day cycles. In the 3 Philadelphia studies, only nulliparous, unmarried women participated. No one who used either oral contraceptives or IUD's was included. In addition, roommates were not permitted to enroll. Thus, only one subject per any combined dorm suite could be enrolled. Calendars were collected at the end of the experiment and the length of each menstrual cycle was calculated and recorded. Each calendar, with its several menses lengths, was then processed again to calculate the average (mean) and standard deviation in cycle length for each subject. All of those calendars with a mean cycle length of 29.5 ± 1 day were selected and analyzed for the purpose of this report. In order to avoid the problem of multiple, non-independent input of data which would spuriously expand on the effect we were evaluating, only one cycle onset per subject was tabulated in this report. For all of the Autumn analyses (1976, 1977, and 1979), the menses onset within the month of October was selected because it is a non-holiday month within the University setting. A tabulation was made to determine how many women had their menses onset on October 1, how many on October 2, October 3, October 4, and so on. Menses Relationship to Moon Cycles* An almanac was used to determine when the new moon had occurred. Once a histogram (frequency count) had been developed for each day in relation to the distance from the new moon (see Table 2) a kernel density analysis (as detailed below) was performed by computer. Thus, each day in October was converted into the "day since new moon" and each day of the lunar cycle could now be represented as to the frequency with which women with 29.5 ±1 day cycles began menstruation. A random distribution would yield a flat density since it would be equally likely for women to begin to menstruate on any day of the lunar cycle. A departure from a straight line thus indicates non-randomness; i.e., whether there was a lunar effect on menstrual onset for these women. The significance of the lunar effect could then be tested. Kernel Density Evaluation* Histograms of lunar menses onset show clustering in that onsets tended to occur in proximity. A kernel density procedure delineates the clustering by smoothing these histograms as in Figures 1 through This content downloaded from 207.46. 13.102 on Sun, 31 Jul 2016 05:06:22 UTC All use subject to http://about.jstor. org/terms 962 / WINNIFRED B. CUTLER ET AL. •af-jl J ? il J * ee NNdt^ 'eVe NNdt^ O ^ N m N|N ° (N 5 A U ? *> sP ^ . A ? *> sP ^ | . A o ? *> *■< go Jl Q 00 tH Os