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Will the Pill Mess Up My Ability to Detect My One True Love?

It’s vacation time for Team Family, as my daughter calls us. While we’re skating and skiing, enjoy this repost from my old blog on hormonal contraceptives and mate choice.

Imagine you are a single, heterosexual woman. You meet a nice man at the driving range, or on a blind date. You like him and he likes you. You date, you get engaged, you get married. You decide to have a child together, so you go off the pill. One morning you wake up and look at your husband, and it’s like seeing him through new eyes. Who is this stranger you married, and what did you ever see in him?

After an article made the news when it suggested mate preferences change on hormonal contraception, this seemed to be the scenario in the heads of many women. Is my pill deceiving me? What if my birth control is making me date the wrong man?

Several articles over the years have demonstrated that women prefer men with more masculine features at midcycle, or ovulation, and more feminine features in less fertile periods. Based on body odor, women and men also often prefer individuals with MHC (major histocompatibility complex) that are different from theirs, which may be a way for them to select mates that will give their offspring an immunological advantage. These findings have been replicated a few times, looking at a few different gendered traits. And as I suggested above, other work has suggested that the birth control pill, which in some ways mimics pregnancy, may mask our natural tendency to make these distinctions and preferences, regarding both masculinity and MHC (Little et al. 2002; Roberts et al. 2008; Wedekind et al. 1995).

On the one hand, I think it’s both interesting and important to consider the implications of the birth control pill beyond just contraception. Hormones are messages, so any cells that have receptors for these messages, like specialized mailboxes, can receive them. The pill is made of synthetic versions of estradiol and progesterone, and there are estradiol and progesterone receptors in your brain. And yes, these hormones do change your brain, both during the natural cycle and on hormonal contraception; Scicurious has written well on this in the past.

On the other hand, I have a lot of questions: First and most important to me, how does any of this translate to non-straight women? I find the constant focus on mate choice between men and women a bit exhausting, and am not sure we can assume non-straight relationships to work the same way. Next, how well do preferences over the cycle map on to actual choices for mates, short term or long term? If we happen to find Brad Pitt more attractive than Justin Bieber at midcycle, does that mean no one will do but Brad Pitt? And finally, what are all the factors that we need to consider in mate choice besides a deep voice or square jawline (again, especially if you try to expand your thinking beyond straight relationships)?

I’ll start with the last two questions that deal with mate preference versus ultimate mate selection. As you all might expect, women and men choose mates for lots of reasons, not just masculinity or complementary immune systems. Bereczkei et al (1997) looked at singles ads and found women often sought mates with high parental care. In a separate singles ad evaluation, Pawlowski and Dunbar (1999) found that women mostly selected men of high resource potential who were interested in long-term relationships (either unlikely to divorce or unlikely to die within twenty years), where men selected women by markers of fecundity (ability to have babies). In a sample of 18-24 year old straight people in the US, Buston and Emlen (2003) found that most people selected mates who had similar characteristics to themselves. And a speed dating sample showed that people under those conditions selected dates based on easily observable traits, like physical attractiveness (Kurzban and Weeden 2005).

Now on to the fact that all of this research is on straight people. I found very little on lesbian women and the menstrual cycle… but what I found was very cool! Brinsmead-Stockham et al (2008) found that, like heterosexual women, lesbian women are quicker to identify unknown faces at midcycle, as long as they were the faces of the sex they preferred. So straight women were good at identifying male faces, lesbian women good at identifying female faces. Burleson et al (2002) found that sexual behavior in lesbian and straight women was mostly similar through the menstrual cycle, with both peaking at midcycle.

So, mate preference may be about telling a research assistant who is the hottest to you at a particular point in your cycle. And it is a fairly robust and consistent finding. However, when it comes to ultimate mate selection the most important thing to consider is a great point made by Pawlowski and Dunbar: finding a mate is about advertising what you have to offer while making known what you want in a mate. Then it’s all about finding some kind of compromise through a series of trade-offs based on what the individual wants, what they can offer, and what’s available in the dating pool. (So, since neither Brad Pitt nor Justin Bieber are currently in the dating pool, my previous comparison was pointless.)

Those of you who met your mate while on the pill: not to fear. I don’t think that the possibility that you may have some suppression of masculinized preferences at one point in your cycle means you’ve chosen the wrong person.

Who knows, it could have opened you up to the Mr. or Ms. Right.

References

Bereczkei T, Voros S, Gal A, and Bernath L. 1997. Resources, Attractiveness, Family Commitment; Reproductive Decisions in Human Mate Choice. Ethology 103(8):681-699.

Brinsmead-Stockham K, Johnston L, Miles L, and Neil Macrae C. 2008. Female sexual orientation and menstrual influences on person perception. Journal of Experimental Social Psychology 44(3):729-734.

Burleson MH, Trevathan WR, and Gregory WL. 2002. Sexual behavior in lesbian and heterosexual women: relations with menstrual cycle phase and partner availability. Psychoneuroendocrinology 27(4):489-503.

Buston PM, and Emlen ST. 2003. Cognitive processes underlying human mate choice: The relationship between self-perception and mate preference in Western society. Proceedings of the National Academy of Sciences 100(15):8805-8810.

Kurzban R, and Weeden J. 2005. HurryDate: Mate preferences in action. Evolution and Human Behavior 26(3):227-244.

Little AC, Jones BC, Penton-Voak IS, Burt DM, and Perrett DI. 2002. Partnership status and the temporal context of relationships influence human female preferences for sexual dimorphism in male face shape. Proceedings of the Royal Society of London Series B: Biological Sciences 269(1496):1095-1100.

Pawlowski B, and Dunbar RIM. 1999. Impact of market value on human mate choice decisions. Proceedings of the Royal Society of London Series B: Biological Sciences 266(1416):281.

Roberts SC, Gosling LM, Carter V, and Petrie M. 2008. MHC-correlated odour preferences in humans and the use of oral contraceptives. Proceedings of the Royal Society B: Biological Sciences 275(1652):2715-2722.

Wedekind C, Seebeck T, Bettens F, and Paepke AJ. 1995. MHC-Dependent Mate Preferences in Humans. Proceedings: Biological Sciences 260(1359):245-249.

2012 Best of Context and Variation

This here blog is many things — ladybusiness explainer, bad science outer, and a place where I reflect on higher education and the academic life. Today is the last day of the semester here at the U of I, there’s a lovely dusting of snow on everything, and it seemed like a nice time to reflect on what I’ve accomplished on the blog, what it’s meant to me, and sometimes what it means to you.

Also, everybody else is doing it.

Ladybusiness anthropology

Here is some legitimate science on pregnancy and rape. On Todd Akin’s brilliant words about the science of conception. This was the most difficult post I have written from an emotional perspective.

When a beginning is not a beginning. My post on the causes of miscarriage. I wrote it for a friend, and, I think, I wrote it for myself.

Don’t sweat it: premenopausal women, reproductive state, and night sweats. My most recent in-depth science blog post, and it was all about ME. While there weren’t too many men interested in this one, this is a post where I got a surprising number of private messages from other women, relieved I had written about night sweats because they got them too. It also opened up a lot of conversations with friends. This is why it can be hard to measure impact or define metrics for this kind of stuff.

Interrupting claims about natural sexual behavior. I probably should just lay this whole kerfuffle to rest, but I was pleased with my final blog post on Deep Thinking Hebephile at the beginning of the year. Whenever anyone evaluates claims about behavior, in evolutionary psych or in other fields, I do hope they remember to keep these tenets of evolutionary theory in mind and test hypotheses against them.

Nutty science

Llama, llama, get with mama: the magical semen ingredient that makes the ladies swoon (then ovulate). I wasn’t debunking anything in this post, which is often the case when I write funnier stuff (well, funnier to me). I just thought it was a great topic, and led to a lot of puns that nauseated adults who either are about my age and therefore saw the same Sesame Street episodes, or have children of their own and are familiar with a current children’s book series. I never said this blog was for everyone!

Hot for Obama, but only when this smug married is not ovulating. On that unfortunate study on voting behavior and ovulation that didn’t measure ovulation.

An academic life

Impostors, the culture of science, and fulfilling our potential. My follow-up post to Sci Foo on the impostor syndrome I and others felt. I was glad to hear that it resonated with a lot of people. I hope we all hold a picture of reality in our heads whenever those ugly feelings come up.

Which came first, rewarding outreach or doing it? On chickens, eggs, and overworked scientists. This was my contribution to a broader conversation on the impact of outreach, and whether it does or should “count” in an academic career.

I can out interdiscipline you: anthropology and the biocultural approach. I was intentionally a bit snarky in this post, to try and get at what it is about some of anthropology’s interdisciplinary work that irks me. Since this post, I have been the reviewer for some amazing interdisciplinary work between biological and cultural anthro. Could it be because of this very post??? Correlation equals causation, yes? Or not.

Finally, a big thank you

Thanks readers, for being here, for supporting me, for being brilliant, interesting people in your own right, and being the kind of people who are eager to learn new things and make the world a better place. Thanks to my allies and friends online and off. Thanks to all those academics who tell me they secretly read me even if it’s not cool for academics to read blogs.

And of course, thanks to my family who have the patience to give me the space to write. Every time I tell my husband something good about my science writing (from “someone with lots more followers retweeted me!” to “I got an honorarium for that speaking gig about the blog!” to “an agent wants to represent me!”), he is delighted. And convinced that some day I am going to write a best seller that allows us to retire to Hawaii.

We can keep him in the dark about what it means to be kinda a little semi-known within a small sub-circle of the science blogosphere, though, because the delight never gets old.

Link love: December 2012

Some interesting, insightful, or amusing things I’ve been reading this week.

The DSM-V is out

I’m not a psychologist, but the DSM, or Diagnostic Systems Manual, is still important to my research, but as someone who teaches evolutionary medicine, most especially my teaching. I have been teaching the shift from the DSM-IV to DSM-V (excuse me, I guess it’s DSM-5 now)  for the past several years, with students doing a close reading of the proposed changes, or projects on some of the new diagnoses. It will be interesting this year to have a finalized document to talk about — as well as the reactions. Two of the main ones I’ll be assigning:

The DSM-5 has been finalized by Vaughan Bell. Bell summarizes the major changes — mostly I can’t believe they took out the bereavement clause for depression.

The New Tamper Tantrum Disorder by David Dobbs. A smart perspective on the pathologizing of normal behavior.

 

Grumble grumble

Why Do Women Leave Biology? This is the page for the press release of an article in BioScience, but it links to the pdf of the manuscript. Shelley Adamo takes a smart look at the factors that drive attrition of female scientists. She suggests that the factors that are blamed for fewer female scientists exist in medicine, but the same gender differences in attrition don’t exist. Adamo claims policy issues drive differences instead (for instance, mandated parental leave seems to reduce attrition in Canada but doesn’t exist in the US). I agree.

A week of a student’s electrodermal activity. Teachers, check out the activity during classes and when sleeping. Decide you’d probably be better napping during your own lecture after all.

How to Email a Professor over at WikiHow. Overall not bad advice. I find it interesting that in the how to address professors section, they tell you how bad it is to call a professor “Mr.,” but only say it’s bad to call a female professor (note professors are default-male) “Mrs.” Personally, I take issue with anything that isn’t Dr. or Prof. if I don’t know the student. Once I know the student, particularly if I advise them, Kate is fine.

Stop Saying That. A great blog post that points out the error of complaining that women should “put as much time and effort into researching their birth as they do researching their next smartphone.”

Sexist humor… leads to more sexism. In the same vein as “stop saying that,” stop permitting sexist humor in your workspace, your home, among your friends. Don’t be a silent witness, and be the guy who interrupts sexism. You don’t have to be obnoxious about it, but if you let it go, you’re telling your friends that being sexist is ok.

I Am the Woman in Your Department Who Does All the Committee Work at McSweeney’s. I didn’t know whether to laugh or cry about this one.

 

Re-emerge from a tough week

Mouse research saves a little girl with leukemia. Because my husband is a two-time cancer survivor, with many of his treatments first being tested in animals, I am grateful to animal researchers every single day.

Your Holiday Mom. A blog that posts letters from parents who love and support LGBTQ kiddos. Have a tissue handy. Also, make it abundantly clear to anyone around you who needs to know it that you are a holiday mom, too, but with actions over words.

How do you pack your bag for a 7 year, 22,000 mile international reporting assignment? Journalist Salopek will walk the “out of Africa” route to South America. I highly recommend a few pairs of Ex Officio underwear — they last for years and you can wash and hang dry them overnight.

The flipped academic: turning higher education on its head. This article describes academics who are doing outreach or making their results available to the public before putting them in academic jargon-speak and up for peer review. Certainly an article that supports those of us that blog, but I didn’t see a clear way the flipped academic was going to push her university to consider her for tenure under that model. Also, why are we into “flipping” so much in academia right now (I’ve also read a few articles on “flipping” the classroom)? Why not call it “inverted” or “transparent” or “outreach-focused?”

And now my favorite post: Michael Eisen puts Darwin’s Tangled Bank in verse. Eisen wrote this poem because his daughter needed to recite a poem for school, and he wanted to give her something scientific and beautiful. He totally wins at parenting. Some day my daughter will learn this, too.

Don’t Sweat It: Premenopausal Women, Reproductive State, and the Joy of Night Sweats


Image of a sweat gland from Gray's Anatomy, 18th edition

Figure 1. Image of a sweat gland from Gray's Anatomy, 18th edition

I tend to go to bed freezing, especially so in the winter, so I pile our flannel sheet, blanket, and down comforter over me when I settle in to sleep. A few times each menstrual cycle, clustered together in the luteal phase between ovulation and menses, I wake up from sleep completely soaked in my own sweat – not a delightful sight or experience. Usually I get up, change pajamas, and try to find a dry spot on the bed to go back to sleep (I promise the sheets eventually get washed, but I’m not about to wake my husband – and sometimes daughter – to change the bed at 3am).

These night sweats started when I was still intensively breastfeeding my daughter and was marathon training, when she was under a year old. At first, I thought it was because we were co-sleeping and we slept next to each other. But I never experienced them next to my husband before that point, and he is a six foot four heat generating machine.

When the marathon was over and I returned to less strenuous activity, breastfeeding frequency was also starting to decline. I didn’t get any night sweats again for quite some time.

Then there was roller derby.

At first, roller derby was a pastime, a recreational activity where I got to learn something totally new and hang out with women I respected. But of course, being the competitive person I am, it became an obsession, and in addition to roller derby practices I was working out quite a lot on my own time. Over the last year I’ve made additional nutritional adjustments to further improve my performance, and I’ve increased the intensity of my off-skates workouts. I work out a minimum of five hours a week, but in the middle of the season it is usually a minimum of nine hours per week.

At about the same time as this increase in physical activity and nutritional improvement, and changes in my body composition, the night sweats came back. With a vengeance.

My advisor once joked that anthropology is a rather navel-gazing discipline, but reproductive ecology, our subfield, is gonad-gazing. There are many times that I have been driven to ask questions in my own research because of physiological phenomena occurring in me, my family, or my friends. My interest in the relationship between reproductive and immune function stemmed from my sister and I both being diagnosed as gluten intolerant almost six years ago. My interest in puberty and adolescence stemmed from me looking ahead to what my preschooler daughter will be dealing with in the next decade. I know many people who have had personal interests in their research, research that might not otherwise have happened if someone hadn’t said, I want to understand why this is happening to me or someone I love. It makes a real case for the importance of diversity among scientists.

Because, guess what? There is almost nothing in the literature on the prevalence of night sweats among healthy premenopausal women. And this sweaty lady wants to get to the bottom of it.

This ain’t my mama’s hot flash

The vast majority of the literature on night sweats is related to the general study of vasomotor symptoms associated with menopause – that is, hot flashes as well as night sweats. Vasomotor symptoms appear to have a pretty similar mechanism and it is a response to the body sensing it is overheated. Blood vessels near the skin’s surface dilate, and sweating can also ensue, to cool it back down again.

Anyone remember when The Cosby Show talked about menopause? That was my introduction to what a hot flash was.

(embed not working for you? video here)

These kinds of symptoms are said to increase in frequency in early menopause. Several studies have shown a negative association between hot flashes and estradiol concentrations, meaning that as estradiol goes down hot flashes go up (Deecher and Dorries 2007; Miller and Duckles 2008). Estradiol naturally declines as a woman gets older, until she reaches menopause when it remains quite low for the rest of her life, and comes from places other than the ovaries. Similar relationships have been found between progesterone and vasomotor symptoms among menopausal women (Hitchcock and Prior 2012; Spark and Willis 2012). Vasomotor symptoms are also associated with depression, panic attacks, and sleep disturbances (Mold et al. 2002). This is likely because vasomotor symptoms can signal some sort of dysregulation in the autonomic nervous system, which is the part of your nervous system that regulates visceral functions like heart rate and, you guessed it, sweating.

The relationship between vasomotor symptoms and exercise, however, is complicated. While I found a few studies that found improvement in menopausal women’s vasomotor symptoms with exercise (Elavsky and McAuley 2005), there were also studies that found no relationship between exercise and vasomotor symptoms (Sternfeld et al. 1999), and still others that found that exercise worsened symptoms (Aiello et al. 2004). The Sternfeld et al (1999) article even found that body mass index was negatively associated with vasomotor symptoms, so the heavier a woman was, the fewer hot flashes she had.

The effects of exercise operate at cross purposes when it comes to vasomotor symptoms. While exercise can improve circulation and be great for your general health, sustained exercise generally leads to at least slight reproductive suppression, and therefore a reduction in progesterone if not also estradiol. The primary way a postmenopausal woman gets endogenous estrogens is from her fat cells, and of course exercise can decrease fat mass. Finally, exercise raises core body temperature, so in some women this could actually trigger vasomotor symptoms.

So if circulatory health is protective, but so are progesterone and estradiol, exercise isn’t going to have the same relationship to vasomotor symptoms in every woman.

Night sweats are about as common in reproductive as perimenopausal women

Here’s the next interesting thing. Hot flashes occur in a slightly higher frequency among menopausal women (32 versus 19%, Mold et al. 2002), which explains why research has tended to focus on them as a menopausal phenomenon. But night sweats occur at a more similar frequency in menopausal and premenopausal women (29 versus 22%, Mold et al. 2002). Check out this figure I made from Table 1 of Mold et al (2002):

Figure 2. Percentage of night sweats reported in women from a research-based sample. Error bars represent 95% confidence intervals – alas, no standard deviation or standard error provided in the manuscript.

Figure 2. Percentage of night sweats reported in women across different age groups from a research-based sample. Error bars represent 95% confidence intervals – alas, no standard deviation or standard error provided in the manuscript.

The frequencies were statistically significantly different here (p < 0.001). But the practical difference is quite small – I mean, night sweats are occurring in almost a quarter of premenopausal women in this sample! To me, this suggests that the idea that night sweats are part of a suite of vasomotor symptoms that appear almost exclusively at menopause is very likely wrong. The question is whether the things that drive all vasomotor symptoms, particularly hot flashes, in menopausal women are also the things that drive night sweats in premenopausal women.

Premenopausal women aren’t all the same

The evidence I mentioned above regarding exercise and vasomotor symptoms certainly corresponds to my experience of night sweats resuming when I changed my diet and increased the duration and intensity of my workouts. Are the ways in which variation in estradiol and progesterone influence menopausal vasomotor symptoms similar in premenopausal women?

To figure this out, I turned to a family planning method. The Fertility Awareness Method uses a combination of basal body temperature and cervical mucus consistency to determine ovulation. It also tends to do a good job delineating the follicular (menses to ovulation) and luteal (ovulation to menses) phases, because many (but not all) ovulatory cycles have a biphasic body temperature pattern, with temperature higher in the luteal phase.

Figure 3. Sample basal body temperature chart, made by me.

Figure 3. Sample basal body temperature chart, made by me.

While it was difficult to find evidence linking hormone concentrations and body temperature, one study did seem to suggest a dose-response relationship, with higher temperature positively correlated with progesterone (Biller et al. 1999). There is also some indication that this change is driven by luteinizing hormone at ovulation, which is certainly correlated with estradiol and progesterone.

In addition to the fact that body temperature is higher in the luteal phase for many women, skin conductance may be higher at this time. Skin conductance measures electrical conductance, which gives one an idea of the moisture of the skin, and thus the activity of the sweat glands (Little and Zahn 1974). Both melatonin and temperature circadian rhythms are a bit different in the luteal phase: the nighttime increase in melatonin, and concurrent temperature increase, are delayed by 90 minutes in women in the luteal phase (Cagnacci et al. 1996). These changes in the timing of melatonin and body temperature could influence the sleep cycle and nighttime vasomotor symptoms.

Women in the luteal phase may also sweat more during exercise (Garcia et al. 2006). In this study, participants were allowed to have water during exercise, which may be why they sweat more, where in other studies where water is restricted core temperature increased in luteal phase women instead. Study authors did not find increased sweating in the luteal phase among women who likely did not ovulate, based on low serum progesterone concentrations.

It makes sense, then, that in some premenopausal women the increase in basal body temperature in the luteal phase could lead to night sweats, particularly if there are other factors that increase their chances. One I found almost by accident is that antihistamine use can increase the incidence of night sweats – I take loratadine almost every day to quell my allergy-induced asthma.

When are we going to pay more attention to reproductive state?

My field works pretty hard to measure global variation in reproductive function, but one understudied group is lactating women. There are some great papers about variation in resumption of ovarian activity with weaning and supplemental feeding  – but what about continued ovarian or endometrial activity during lactation? Since breastfeeding is usually part of our exclusion criteria, we know little of the effect of lactation on reproductive function except in the most basic ways, and even less on vasomotor symptoms. I did find a single letter to the editor in American Family Physicians from a physician saying that he found many of his breastfeeding patients report night sweats (Taylor 2003).

Two factors drive the resumption of reproductive function in lactating women: prolactin levels and energy balance(Valeggia and Ellison 2001). Each breastfeeding bout brings on a spike in prolactin, which suppresses ovarian function. Closely spaced breastfeeding bouts can then impact ovarian function. However, the factor that seems to multiply the prolactin effect is whether the lactating woman is also in any kind of energetic deficit – either because she is exercising or doing physical work, or not getting enough food to replace her work and the 400-600 calories she burns a day making milk. Prolactin, then, was where I wanted to look next.

Prolactin concentrations vary through the ovulatory menstrual cycle, where it decreases from the late follicular into the midluteal phase (Bäckström et al. 2008), meaning prolactin is lower in the luteal phase. High prolactin concentrations, or hyperprolactinemia, are a signal of infertility. Hyperprolactinemia is most often caused by a small mass on the pituitary gland, and there are therapeutic interventions that resolve it easily. But it is possible to have higher prolactin concentrations within the range of normal just by performing a lot of physical activity (Rojas Vega et al. 2012). Similar to a breastfeeding bout, prolactin increases with physical activity, stays high for a short period during recovery, and then declines again.

My weekday roller derby practices are late at night, one not ending until 10:30pm. Further, normal body temperature gets set a little higher after exercise (Haight and Keatinge 1973). The post-exercise drop in prolactin that is occurring while I’m asleep, along with my elevated exercise and luteal basal body temperature while I’m huddled under all my blankets, could trigger night sweats.

Conclusion

Changes in body temperature and prolactin from late night exercise, combined with higher basal body temperature in the luteal phase and antihistamine administration, could all contribute to the hot mess that has led to my night sweats. What I enjoyed about this foray into blatant navel/gonad/sweat gland-gazing was that it got me thinking about the ways in which the menstrual cycle affects the autonomic nervous system, and that I ended up learning a lot more about prolactin than I’d known before. I may need to measure prolactin and basal body temperature in future research projects, now that I know the kinds of factors that affect their variation, and their downstream effects.

Knowing the factors that may be contributing to my night sweats doesn’t necessarily mean I can prevent them, since I won’t be quitting roller derby night practices or allergy meds any time soon. But I can play around with ways to lower my body temperature on nights when I know it’s most likely – which may mean giving up my beloved down comforter.

References

Aiello EJ, Yasui Y, Tworoger SS, Ulrich CM, Irwin ML, Bowen D, Schwartz RS, Kumai C, Potter JD, and McTiernan A. 2004. Effect of a yearlong, moderate-intensity exercise intervention on the occurrence and severity of menopause symptoms in postmenopausal women. Menopause 11(4):382-388.

Bäckström C, McNeilly A, Leask R, and Baird D. 2008. Pulsatile secretion of LH, FSH, prolactin, oestradiol and progesterone during the human menstrual cycle. Clinical Endocrinology 17(1):29-42.

Biller B, Luciano A, Crosignani P, Molitch M, Olive D, Rebar R, Sanfilippo J, Webster J, and Zacur H. 1999. Guidelines for the diagnosis and treatment of hyperprolactinemia. The Journal of reproductive medicine 44(12 Suppl):1075.

Cagnacci A, Soldani R, Laughlin GA, and Yen S. 1996. Modification of circadian body temperature rhythm during the luteal menstrual phase: role of melatonin. Journal of Applied Physiology 80(1):25-29.

Deecher D, and Dorries K. 2007. Understanding the pathophysiology of vasomotor symptoms (hot flushes and night sweats) that occur in perimenopause, menopause, and postmenopause life stages. Archives of Women’s Mental Health 10(6):247-257.

Elavsky S, and McAuley E. 2005. Physical activity, symptoms, esteem, and life satisfaction during menopause. Maturitas 52(3–4):374-385.

Garcia A, Lacerda M, Fonseca I, Reis F, Rodrigues L, and Silami-Garcia E. 2006. Luteal phase of the menstrual cycle increases sweating rate during exercise. Brazilian Journal of Medical and Biological Research 39:1255-1261.

Haight JSJ, and Keatinge WR. 1973. Elevation in set point for body temperature regulation after prolonged exercise. The Journal of Physiology 229(1):77-85.

Hitchcock CL, and Prior JC. 2012. Oral micronized progesterone for vasomotor symptoms—a placebo-controlled randomized trial in healthy postmenopausal women. Menopause 19(8):886-893.

Little BC, and Zahn TP. 1974. Changes in mood and autonomic functioning during the menstrual cycle. Psychophysiology 11(5):579-590.

Miller VM, and Duckles SP. 2008. Vascular actions of estrogens: functional implications. Pharmacological reviews 60(2):210-241.

Mold JW, Mathew MK, Belgore S, and Dehaven M. 2002. Prevalence of night sweats in primary care patients. J Fam Pract 51:452-456.

Rojas Vega S, Hollmann W, and Strüder HK. 2012. Influences of Exercise and Training on the Circulating Concentration of Prolactin in Humans. Journal of Neuroendocrinology 24(3):395-402.

Spark MJ, and Willis J. 2012. Systematic review of progesterone use by midlife and menopausal women. Maturitas 72(3):192-202.

Sternfeld B, Quesenberry Jr CP, and Husson G. 1999. Habitual physical activity and menopausal symptoms: a case-control study. Journal of women’s health 8(1):115-123.

Taylor RD. 2003. Common causes of night sweats in various populations. Am Fam Physician 68(7):1264.

Valeggia CR, and Ellison PT. 2001. Lactation, energetics, and postpartum fecundity. In: Ellison PT, editor. Reproductive ecology and human evolution. New York: Aldine de Gruyter. p 85-106.

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