Acetaminophen does not affect 24-h body temperature or sleep in the luteal phase of the menstrual cycle.

Body temperature and sleep change in association with increased progesterone in the luteal phase of the menstrual cycle in young women. The mechanism by which progesterone raises body temperature is not known but may involve prostaglandins, inducing a thermoregulatory adjustment similar to that of fever. Prostaglandins also are involved in sleep regulation and potentially could mediate changes in sleep during the menstrual cycle. We investigated the possible role of central prostaglandins in mediating menstrual-associated 24-h temperature and sleep changes by inhibiting prostaglandin synthesis with a therapeutic dose of the centrally acting cyclooxygenase inhibitor acetaminophen in the luteal and follicular phases of the menstrual cycle in young women. Body temperature was raised, and nocturnal amplitude was blunted, in the luteal phase compared with the follicular phase. Acetaminophen had no effect on the body temperature profile in either menstrual cycle phase. Prostaglandins, therefore, are unlikely to mediate the upward shift of body temperature in the luteal phase. Sleep changed during the menstrual cycle: on the placebo night in the luteal phase the women had less rapid eye movement sleep and more slow-wave sleep than in the follicular phase. Acetaminophen did not alter sleep architecture or subjective sleep quality. Prostaglandin inhibition with acetaminophen, therefore, had no effect on the increase in body temperature or on sleep in the midluteal phase of the menstrual cycle in young women, making it unlikely that central prostaglandin synthesis underlies these luteal events.     

Diurnal and menstrual cycles in body temperature are regulated differently: A 28-day ambulatory study in healthy women with thermal discomfort of cold extremities and controls

Diurnal cycle variations in body-heat loss and heat production, and their resulting core body temperature (CBT), are relatively well investigated; however, little is known about their variations across the menstrual cycle under ambulatory conditions. The main purpose of this study was to determine whether menstrual cycle variations in distal and proximal skin temperatures exhibit similar patterns to those of diurnal variations, with lower internal heat conductance when CBT is high, i.e. during the luteal phase. Furthermore, we tested these relationships in two groups of women, with and without thermal discomfort of cold extremities (TDCE). In total, 19 healthy eumenorrheic women with regular menstrual cycles (28–32 days), 9 with habitual TDCE (ages 29?±?1.5 year; BMI 20.1?±?0.4) and 10 controls without these symptoms (CON: aged 27?±?0.8 year; BMI 22.7?±?0.6; p?<?0.004 different to TDCE) took part in the study. Twenty-eight days continuous ambulatory skin temperature measurements of distal (mean of hands and feet) and proximal (mean of sternum and infraclavicular regions) skin regions, thighs, and calves were carried out under real-life, ambulatory conditions (i-Buttons® skin probes, sampling rate: 2.5?min). The distal minus proximal skin temperature gradient (DPG) provided a valuable measure for heat redistribution from the core to the shell, and, hence, for internal heat conduction. Additionally, basal body temperature was measured sublingually directly after waking up in bed. Mean diurnal amplitudes in skin temperatures increased from proximal to distal skin regions and the 24-h mean values were inversely related. TDCE compared to CON showed significantly lower hand skin temperatures and DPG during daytime. However, menstrual cycle phase did not modify these diurnal patterns, indicating that menstrual and diurnal cycle variations in skin temperatures reveal additive effects. Most striking was the finding that all measured skin temperatures, together with basal body temperature, revealed a similar menstrual cycle variation (independent of BMI), with highest and lowest values during the luteal and follicular phases, respectively. These findings lead to the conclusion that in contrast to diurnal cycle, variations in CBT variation across the menstrual cycle cannot be explained by changes in internal heat conduction under ambulatory conditions. Although no measurements of metabolic heat production were carried out increased metabolic heat generation during the luteal phase seems to be the most plausible explanation for similar body temperature increases.     

Effects of the menstrual cycle on muscle recruitment and oxidative fuel selection during cold exposure

Differences in core temperature and body heat content, generally observed between the luteal and follicular phase of the menstrual cycle, have been reported to modulate the thermogenic activity of cold-exposed women. However, it is unclear how this change in whole body shivering activity will influence fuel selection. The goal of this study was to quantify the effects of the menstrual cycle on muscle recruitment and oxidative fuel selection during low-intensity shivering. Electromyographic activity of eight large muscles was monitored while carbohydrate, lipid, and protein utilization was simultaneously quantified in the follicular and luteal phases of the menstrual cycle in nonacclimatized women shivering at a low intensity. The onset (～25 min), intensity (～15% of maximal voluntary contraction), and pattern (～6 shivering bursts/min) of the shivering response did not differ between menstrual cycle phases, regardless of differences in core temperature and hormone levels. This resulted in lipids remaining the predominant substrate, contributing 75% of total heat production, independent of menstrual phase. We conclude that hormone fluctuations inherent in the menstrual cycle do not affect mechanisms of substrate utilization in the cold. Whether the large contribution of lipids to total heat production in fuel selection confers a survival advantage remains to be established.     

Non-Advertized does not Mean Concealed: Body Odour Changes across the Human Menstrual Cycle

Females of a number of primate species display their fertile period by behavioural and/or morphological changes. Traditionally, the fertile period in human females has been considered to be concealed. However, this presumption has rarely been tested. One of the possible mechanisms for assessing menstrual cycle phase is through the sense of smell. In this study possible changes in odour across the menstrual cycle were investigated. Samples of body odour were acquired from 12 women (aged 19–27 yr), none of whom were using hormonal contraceptives. Samples were collected using cotton pads worn in the armpit for 24 h, from the menstrual, follicular and luteal cycle phases. Our experimental sample of 42 males (age 19–34 yr) repeatedly rated these odour samples for their intensity, pleasantness, attractiveness and femininity. Raw subjective smell ratings from each man were transformed to z‐scores. Subsequently, these z‐scores were tested by the general linear mixed‐model analysis (PROC MIXED, SAS) with the female's ID nested within the subject's ID as a random factor to account for the repeated measures of the subjects. Significant changes across the cycle were found for ratings of pleasantness [F_(2,689) = 702; p = 0.001], attractiveness [F(2,546) = 6.35; p = 0.002] and intensity [F(2,530) = 3.57; p = 0.028]. Odour from women in the follicular (i.e. fertile) phase was rated as the least intense and the most attractive. Subsequent post hoc analysis revealed significant differences in intensity, pleasantness and attractiveness between the menstrual phase and the follicular phase, and in pleasantness and attractiveness between the menstrual and luteal phases. Significant difference between the follicular and the luteal phase was found only for attractiveness. Our results suggest that men can potentially use smell as a mechanism for monitoring menstrual cycle phase in current or prospective sexual partners. Therefore, the fertile period in humans should be considered non‐advertized, rather than concealed.     

Predominance of distal skin temperature changes at sleep onset across menstrual and circadian phases

Menstrual cycle-associated changes in reproductive hormones affect body temperature in women. We aimed to characterize the interaction between the menstrual, circadian, and scheduled sleep-wake cycles on body temperature regulation. Eight females entered the laboratory during the midfollicular (MF) and midluteal (ML) phases of their menstrual cycle for an ultradian sleep-wake cycle procedure, consisting of 36 cycles of 60-minute wake episodes alternating with 60-minute nap opportunities, in constant bed-rest conditions. Core body temperature (CBT) and distal skin temperature (DT) were recorded and used to calculate a distal-core gradient (DCG). Melatonin, sleep, and subjective sleepiness were also recorded. The circadian variation of DT and DCG was not affected by menstrual phase. DT and DCG showed rapid, large nap episode-dependent increases, whereas CBT showed slower, smaller nap episode-dependent decreases. DCG values were significantly reduced for most of the wake episode in an overall 60-minute wake/60-minute nap cycle during ML compared to MF, but these differences were eliminated at the wake-to-nap lights-out transition. Nap episode-dependent decreases in CBT were further modulated as a function of both circadian and menstrual factors, with nap episode-dependent deceases occurring more prominently during the late afternoon/evening in ML, whereas nap episode-dependent DT and DCG increases were not significantly affected by menstrual phase but only circadian phase. Circadian rhythms of melatonin secretion, DT, and DCG were significantly phase-advanced relative to CBT and sleep propensity rhythms. This study explored how the thermoregulatory system is influenced by an interaction between circadian phase and vigilance state and how this is further modulated by the menstrual cycle. Current results agree with the thermophysiological cascade model of sleep and indicate that despite increased CBT during ML, heat loss mechanisms are maintained at a similar level during nap episodes, which may allow for comparable circadian sleep propensity rhythms between menstrual phases.     

Physical activity of adult female rhesus monkeys (Macaca mulatta) across the menstrual cycle

Physical activity is an important physiological variable impacting on a number of systems in the body. In rodents and several species of domestic animals, levels of physical activity have been reported to vary across the estrous cycle; however, it is unclear whether such changes in activity occur in women and other primates across the menstrual cycle. To determine whether significant changes in activity occur over the menstrual cycle, we continuously measured physical activity in seven adult female rhesus monkeys by accelerometry over the course of one menstrual cycle. Monkeys were checked daily for menses, and daily blood samples were collected for measurement of reproductive hormones. All monkeys displayed ovulatory menstrual cycles, ranging from 23 to 31 days in length. There was a significant increase in estradiol from the early follicular phase to the day of ovulation (F(1.005,5.023) = 40.060, P = 0.001). However, there was no significant change in physical activity across the menstrual cycle (F(2,12) = 0.225, P = 0.802), with activity levels being similar in the early follicular phase, on the day of the preovulatory rise in estradiol and during the midluteal phase. Moreover, the physical activity of these monkeys was not outside the range of physical activity that we measured in 15 ovariectomized monkeys. We conclude that, in primates, physical activity does not change across the menstrual cycle and is not influenced by physiological changes in circulating estradiol. This finding will allow investigators to record physical activity in female primates without the concern of controlling for the phase of the menstrual cycle.     

Plasma insulin and glucagon concentrations and biochemical variables in regularly menstruating females with ovulatory and anovulatory menstrual cycles.

Ovarian hormones are known to affect endocrine pancreas function. However, data concerning the effects of anovulatory menstrual cycles in regularly menstruating women on endocrine pancreas and blood metabolites are lacking. We examined plasma insulin, glucagon, glucose, lactate, urea and glycerol concentrations in reproductive-age, regularly menstruating females classified as ovulating or non-ovulating on the basis of basal body temperature measurements and plasma 17beta-estradiol and progesterone determinations. All measurements were performed twice--in the follicular and again in the luteal phases of the menstrual cycle. There were no differences in plasma lactate and glycerol concentrations between the two groups of subjects. Plasma insulin concentrations tended to be lower in non-ovulating than in ovulating women. In addition, plasma glucagon did not differ in the follicular (33.2 pmol/l) or luteal phase of the menstrual cycle in females with disturbed ovarian hormone secretion (34.1 pmol/l). In contrast, plasma glucagon concentrations in the luteal phase (32.8 pmol/l) were significantly higher than in the follicular phase (24.9 pmol/l) of the menstrual cycle in ovulating women. Plasma glucose concentrations in the follicular phase of the menstrual cycle in non-ovulating women (4.1 mmol/l) were slightly but significantly lower than in their ovulating counterparts (5.3 mmol/l). Furthermore, no correlations were noted between plasma glucose and insulin-to-glucagon molar ratio in non-ovulating subjects. Plasma urea concentrations in non-ovulating women were markedly lower than in ovulating women in both follicular and luteal phases of the menstrual cycle (4.1 and 3.9 mmol/l vs. 5.3 and 5.4 mmol/l in non-ovulating and ovulating women, respectively). In ovulating women, plasma urea levels in both cycle phases were significantly correlated with plasma glucagon concentrations, but no such correlation was found in non-ovulating women. In conclusion, anovulatory menstrual cycles in premenopausal females slightly altered pancreatic hormone plasma levels but markedly impaired their action on plasma glucose and urea concentrations.     

Pathogen disgust,but not moral disgust,changes across the menstrual cycle

The Compensatory Prophylaxis Hypothesis (CPH) proposes that during periods of increased susceptibility to infections, e.g., during the luteal phase of the menstrual cycle when progesterone suppresses immune function, women should feel more disgust toward pathogen cues and behave prophylactically. We investigate differences in disgust sensitivity and contamination sensitivity during different phases of the menstrual cycle in regularly cycling, healthy 93 rural and urban Polish women using the within-subject design. Disgust sensitivity was measured during two different phases of a menstrual cycle: 1) the follicular phase (the 5th or 6th day of the cycle) and 2) the luteal phase (on the 5th day after a positive ovulatory test or on 20th day of a cycle if the result of the ovulatory test was not positive). In the luteal phase, women scored higher on the Pathogen Disgust of the Three-Domain Disgust Scale, the Contamination Obsessions and Washing Compulsions Subscale of Padua Inventory, and on ratings of photographs showing sources of potential infections than in the follicular phase. Moral Disgust of the Three-Domain Disgust Scale did not differ between cycle phases. Hence, results suggest that women feel more disgusted toward cues to pathogens during the luteal phase, when susceptibility to infection is greater. We suggest that it is necessary to incorporate ovulatory testing as well as to conduct repeated measurements of disgust sensitivity in future tests of the CPH. Moreover, we believe that understanding how the feeling of pathogen disgust varies across the menstrual cycle and in relation to progesterone levels could be useful in designing effective infectious diseases prevention strategies for women.     

Effects of menstrual cycle phase and oral contraceptive use on verbal memory

Surgical or pharmacological suppression of ovarian hormones leads to declines in verbal memory, and estrogen treatment reverses these deficits. In the current study, we investigated the effects of menstrual cycle phase and oral contraceptives on verbal memory, as measured by the California Verbal Learning Test, in two groups of premenopausal women — 16 naturally cycling women and 20 current users of estrogen-based oral contraceptives (OCs). Naturally cycling women were assessed twice — once during the early follicular phase (Days 2-4) and once during the midluteal phase (Days 20-22) of the menstrual cycle. OC users were tested on the same cycle days, corresponding to inactive and active pill phases, respectively. We predicted that naturally cycling women would show improved verbal memory during the midluteal phase, when estradiol levels are high, compared with the follicular phase, when estradiol levels are low. We also predicted that OC users, who show no change in endogenous estradiol across the cycle, would show no change in verbal memory. Contrary to predictions, naturally cycling women showed no changes in verbal memory across the cycle, whereas OC users showed enhanced memory during the active pill phase (p < .05). None of the secondary cognitive outcome measures varied with cycle phase or OC use including measures of visuospatial memory, verbal fluency, visuospatial abilities, and attention. Overall, these results suggest that verbal memory performance in premenopausal women varies across the cycle with OC use, but does not vary systematically with changes in endogenous estradiol.     

Do Women's Voices Provide Cues of the Likelihood of Ovulation? The Importance of Sampling Regime

The human voice provides a rich source of information about individual attributes such as body size, developmental stability and emotional state. Moreover, there is evidence that female voice characteristics change across the menstrual cycle. A previous study reported that women speak with higher fundamental frequency (F0) in the high-fertility compared to the low-fertility phase. To gain further insights into the mechanisms underlying this variation in perceived attractiveness and the relationship between vocal quality and the timing of ovulation, we combined hormone measurements and acoustic analyses, to characterize voice changes on a day-to-day basis throughout the menstrual cycle. Voice characteristics were measured from free speech as well as sustained vowels. In addition, we asked men to rate vocal attractiveness from selected samples. The free speech samples revealed marginally significant variation in F0 with an increase prior to and a distinct drop during ovulation. Overall variation throughout the cycle, however, precluded unequivocal identification of the period with the highest conception risk. The analysis of vowel samples revealed a significant increase in degree of unvoiceness and noise-to-harmonic ratio during menstruation, possibly related to an increase in tissue water content. Neither estrogen nor progestogen levels predicted the observed changes in acoustic characteristics. The perceptual experiments revealed a preference by males for voice samples recorded during the pre-ovulatory period compared to other periods in the cycle. While overall we confirm earlier findings in that women speak with a higher and more variable fundamental frequency just prior to ovulation, the present study highlights the importance of taking the full range of variation into account before drawing conclusions about the value of these cues for the detection of ovulation.     

Isometric strength and endurance during the menstrual cycle.

Seven healthy young women, 3 whom had been taking oral contraceptives, were examined during the course of 2 menstrual cycles to assess their isometric strength, their endurance during a series of 5 fatiguing isometric contractions at a tension of 40% MVC, and their blood pressures and heart rates during those fatiguing contractions. Two sets of experiments were performed, one in which the subject's forearm temperature was allowed to vary as a function of T A, and one with the muscle temperature stabilized by immersion of the forearm in water at 37 degrees C. During exposure to ambient temperatures, isometric strength and both the heart rate and blood pressure responses at rest and at the end of a fatiguing, sustained isometric exercise, were not significantly different during any phase of the menstrual cycle in any subject. In contrast, the isometric endurance in the women not taking oral contraceptives varied sinusoidally in all 5 contractions with a peak endurance midway through the ovulatory phase and the lowest endurance mid-way through the luteal phase of the menstrual cycle. The isometric endurance of the women taking oral contraceptives did not vary during their menstrual cycle. After stabilization of the temperature of the muscles of the forearm in water at 37 degrees C, the isometric endurance of the normal subjects showed a hyperbolic response with the maximal endurance at the beginning and end of their cycles, and the shortest endurance at mid-cycle. Here again, however, the isometric endurance of the women taking oral contraceptives did not vary after immersion of their forearms in the 37 degree C water.     

A change of osteocalcin (OC) and tartrate resistant acid phosphatase 5b (TRACP-5b) with the menstrual cycle

Bone metabolism markers associated with 4 menstrual cycle phases were evaluated in 14 healthy young females without menstrual disorder. Menstrual cycle phases were confirmed with basal body temperature for 3 months, luteinizing hormone kits, and sexual hormone concentrations of serum. The bone metabolism markers used were osteocalcin (OC), which was measured by immunoradiometric assay (IRMA), and tartrate resistant acid phosphatase 5b (TRACP-5b), which was measured by enzyme immunometric assay (EIA). The highest values of OC and TRACP-5b were observed in the ovulation phase, and TRACP-5b increased significantly when compared with levels in the menstrual phase (p<0.05). Furthermore, the changes in sex-hormone secretion involved in OC and TRACP-5b showed specific patterns during the menstrual cycle. In other words, TRACP-5b levels are influenced by sex hormones produced during the menstrual period and are based on the bone-formation status. Therefore, it is presumed that the TRACP-5b levels during ovulation play a central role in bone formation and bone metabolism.     

Effects of the menstrual cycle on auditory event-related potentials

Gonadal steroids (estradiol and progesterone) can alter neuronal functioning, but electrophysiological evidence in women is still sparse. Therefore, the present study investigated event-related potentials (ERPs) to neutral stimuli over the course of the menstrual cycle. In addition, associations between ERPs and salivary estradiol and progesterone concentrations were investigated. Eighteen young healthy women were tested at three different phases of their menstrual cycle (menses, and follicular and luteal phases). ERPs (i.e., the N1 and P2 components, reflecting cortical arousal and the orienting response, the N2, P3, and the Slow Wave (SW), reflecting controlled processing) were measured using two different paradigms. In the luteal phase, early ERPs reflecting the cortical arousal response were diminished in the first stimulus block indicating an attenuated orienting response. These changes were significantly correlated with estradiol as well as progesterone levels. As to the later ERP components, the N2 latency was shorter during menses compared to the other two phases. No menstrual cycle-associated changes were apparent in other late ERP components. In sum, this study documents changes in auditory ERPs across the menstrual cycle with the most prominent changes occurring during the luteal phase. Future ERP studies therefore need to be more attentive to the issue of menstrual phase when studying female subjects or female patients.     

Seasonality on Mood and Length of Menstrual Cycle in Tropical Young Women

In order to know whether seasonal variations affect mood and the length of the menstrual cycle in tropical young women, we have conducted a survey with 200 female students in Hanoi, Vietnam. We used the Vietnamese-translated Self-rating Depression Scale (SDS) for the measurements of their mood. Each of them was given a calendar (from September, 1999 to August, 2000) and was instructed to circle the first day of their menstruation, each month. The results showed that there existed a high prevalence of summer Seasonal Affective Disorder (SAD) and that the length of the menstrual cycle was affected by seasonal change. The average lengths of menstrual cycles were 30.7 ± 0.3 days (mean ± SEM) which is longer than in American young women. The higher occurrence of summer SAD seems to be related to the high ambient temperature during summer in the tropics, influencing their mood.     

Luteal phase of the menstrual cycle in young healthy women is associated with decline in interleukin 2 levels.

The aim of this study was to look at the possible changes in the blood levels of Interleukin 2 (IL2) during the sexual cycle in generally healthy, young, regularly menstruating women. The concentrations of progesterone and 17beta-estradiol were measured using radioimmunological assay. The bioactivity of interleukin 2 was measured using a biological test on the IL2-sensitive CTLL cell line. The percentage of lymphocytes with intracellular IL2 was determined by flow cytometry. Eighteen healthy volunteers (19-29 years old) were examined on days 5, 8, 14, 18 and 25 of the same cycle. All women were characterised by a regular menstrual cycle as per physiological levels of 17beta-es-tradiol and progesterone. The luteal phase of the cycle was characterised by both a decrease of IL2 blood levels and a decrease in the percentage of intracellular 1L2-containing lymphocytes stimulated in vitro. The IL2 level fluctuations observed during the menstrual cycle may be one factor causing pre-menstrual infections observed in young women. On the other hand, the decrease of IL2 may be seen as a start of the immune suppression necessary for an embryo's nidation.     

Body Temperature and Physical Activity Correlates of the Menstrual Cycle in Chacma Baboons (Papio hamadryas ursinus)

We investigated the temporal relationship between abdominal temperature, physical activity, perineal swelling, and urinary progesterone and estradiol concentrations over the menstrual cycle in unrestrained captive baboons. Using a miniature temperature‐sensitive data logger surgically implanted in the abdominal cavity and an activity data logger implanted subcutaneously on the trunk, we measured, continuously over 6 months at 10‐min intervals, abdominal temperature and physical activity patterns in four female adult baboons Papio hamadryas ursinus (12.9–19.9 kg), in cages in an indoor animal facility (22–25°C). We monitored menstrual bleeding and perineal swelling changes, and measured urinary progesterone and estradiol concentrations, daily for up to 6 months, to ascertain the stage and length of the menstrual cycle. The menstrual cycle was 36 ± 2 days (mean ± SD) long and the baboons exhibited cyclic changes in perineal swellings, abdominal temperature, physical activity, urinary progesterone, and estradiol concentrations over the cycle. Mean 24‐hr abdominal temperature during the luteal phase was significantly higher than during the periovulatory phase (ANOVA, F_{(2, 9)} = 4.7; P = 0.04), but not different to that during the proliferative phase. Physical activity followed a similar pattern, with mean 24‐hr physical activity almost twice as high in the luteal than in the periovulatory phase (ANOVA, P = 0.58; F_{(2, 12)} = 5.8). We have characterized correlates of the menstrual cycle in baboons and shown, for the first time, a rhythm of physical activity and abdominal temperature over the menstrual cycle, with a nadir of temperature and activity at ovulation. Am. J. Primatol. 74:1143‐1153, 2012. © 2012 Wiley Periodicals, Inc.     

Progesterone,fluid, and electrolytes in premenstrual syndrome.

Changes in mood, plasma progesterone concentration, urinary volume, sodium excretion, sodium:potassium ratio, and body weight during the menstrual cycle were determined in 18 women with premenstrual syndrome and 10 symptomless (control group) women. Plasma progesterone concentration was higher in the women with symptoms during the postovulatory phase of the cycle, and the peak progesterone concentration appeared earlier. The changes in progesterone concentration were accompanied by a natriuresis and diuresis that fell towards preovulatory values in the premenstrual phase. Sodium retention was not confined to any definite period. Mood symptoms occurred after the changes in progesterone and electrolyte concentrations. Progesterone deficiency is probably not the cause of premenstrual syndrome. Thus treatment with progesterone is probably illogical unless a deficiency is detected. Treatment should be aimed at preventing the natriuretic effect of progesterone in the postovulatory phase and the sodium-retaining and water-retaining effects of aldosterone in the premenstrual phase.     

Changes in the density gradient distribution of erythrocytes during the menstrual cycle

Modifications in erythrocyte density distribution were evaluated, by means of centrifugation on Ficoll-Triosil discontinuous density gradient, in five healthy young women during menstrual cycle. Oestradiol and progesterone plasma levels were tested, showing normal and typically ovulatory-like variations during the cycle. Youngest cell populations showed always quantitative increases from the follicular to the ovulatory phase of the cycle, reverting to basal values in the luteal phase. Possible hormonal or haemorrhagic causes are discussed.     

Effect of Sex, Menstrual Cycle Phase, and Oral Contraceptive Use on Circadian Temperature Rhythms

The circadian rhythm of rectal temperature was continuously recorded over several consecutive days in young men and women on regular nocturnal sleep schedules. There were 50 men, 21 women with natural menstrual cycles [i.e., not taking oral contraceptives (OCs) (10 in the follicular phase and 11 in the luteal phase)], and 14 women using OCs (6 in the pseudofollicular phase and 8 in the pseudoluteal phase). Circadian phase and amplitude were estimated using a curve-fitting procedure, and temperature levels were determined from the raw data. A two-way analysis of variance (ANOVA) on the data from the four groups of women, with factors menstrual cycle phase (follicular, luteal) and OC use (yes, no), showed that temperature during sleep was lower during the follicular phase than during the luteal phase. Since waking temperatures were similar in the two phases, the circadian amplitude was also larger during the follicular phase. The lower follicular phase sleep temperature also resulted in a lower 24-h temperature during the follicular phase. The two-way ANOVA showed that temperature during sleep and 24-h temperature were lower in naturally cycling women than in women taking OCs. A one-way ANOVA on the temperature rhythm parameters from the five groups of subjects showed that the temperature rhythms of the men and of the naturally cycling women in the follicular phase were not significantly different. Both of these groups had lower temperatures during sleep, lower 24-h temperatures, and larger circadian amplitudes than the other groups. There were no significant differences in circadian phase among the five groups studied. In conclusion, menstrual cycle phase, OC use, and sex affect the amplitude and level, but not the phase, of the overt circadian temperature rhythm.     

Effect of Sex,Menstrual Cycle Phase,and Oral Contraceptive Use on Circadian Temperature Rhythms

The circadian rhythm of rectal temperature was continuously recorded over several consecutive days in young men and women on regular nocturnal sleep schedules. There were 50 men, 21 women with natural menstrual cycles [i.e., not taking oral contraceptives (OCs) (10 in the follicular phase and 11 in the luteal phase)], and 14 women using OCs (6 in the pseudofollicular phase and 8 in the pseudoluteal phase). Circadian phase and amplitude were estimated using a curve-fitting procedure, and temperature levels were determined from the raw data. A two-way analysis of variance (ANOVA) on the data from the four groups of women, with factors menstrual cycle phase (follicular, luteal) and OC use (yes, no), showed that temperature during sleep was lower during the follicular phase than during the luteal phase. Since waking temperatures were similar in the two phases, the circadian amplitude was also larger during the follicular phase. The lower follicular phase sleep temperature also resulted in a lower 24-h temperature during the follicular phase. The two-way ANOVA showed that temperature during sleep and 24-h temperature were lower in naturally cycling women than in women taking OCs. A one-way ANOVA on the temperature rhythm parameters from the five groups of subjects showed that the temperature rhythms of the men and of the naturally cycling women in the follicular phase were not significantly different. Both of these groups had lower temperatures during sleep, lower 24-h temperatures, and larger circadian amplitudes than the other groups. There were no significant differences in circadian phase among the five groups studied. In conclusion, menstrual cycle phase, OC use, and sex affect the amplitude and level, but not the phase, of the overt circadian temperature rhythm.