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I don’t have a 28-day menstrual cycle, and neither should you

The views expressed are those of the author and are not necessarily those of Scientific American.


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Most of us are familiar with a 28-day menstrual cycle, which, divided in half, comprises the follicular phase – that’s when the dominant follicle, or egg, is growing and preparing for ovulation – and the luteal phase – when the endometrium, or lining of the uterus, is preparing for possible conception and implantation. If implantation doesn’t occur and signal pregnancy to the corpus luteum, which is the "yellow body" left behind by the ovulated egg, then it eventually degrades, hormone levels decline, and menstruation occurs. Then the whole process starts up again.

However, the frequency of such a cycle in any given woman’s life, in any given month, is pretty low. This contradicts what we learned in health class and sex ed, and sometimes the things girls and women hear from peers, parents, and doctors. Most young girls just getting their period take years to achieve regular cycles like the one I described above: this is the main characteristic of the reproductive functioning of adolescents. Yet this normal variation sets us up for a lifetime of checking our cycle, counting days, doubting that we’re like other girls, and feeling bad about ourselves, because of that early information that we should be achieving twenty-eight-day cycles regularly.

When I first became an anthropology major in college, I remember being nearly overwhelmed with data on the different factors that produce variation in women’s hormone levels and cycle lengths: our reproductive functioning is influenced by how much we eat [1], how much we exercise [2], whether we are trying to lose weight [3], and whether we are recreational athletes [4]. Some studies even show an influence of psychological stress on cycle length [5].

What also interested me was that we could measure a lot of variation between populations that appeared to be based not on genetics, but on lifestyle. Women in rural southern Poland, which is the population I study, have cycles on average about the same length as ours, maybe a touch shorter, but their progesterone concentrations are lower, our data suggest they may not maintain their endometrial thickness through their luteal phase the way women in industrial populations do [6, 7]. This is because I do my fieldwork in the summer months, when they are working long hours in the fields harvesting. Much of their work must be done by hand, and men and women work equally hard at farming. So even though their body weight and body mass index are about the same, and they eat about the same number of calories as those of us sitting at desk jobs in the US, their hard work and energy constraint is like a signal to their bodies that they should not allocate too much finite resource to reproduction.

When I learned these things in college, and then saw it firsthand in my own fieldwork and lab results in graduate school and beyond, it wasn’t all new information. Women are aware that lifestyle and other factors affect their bodies. However, the signal we tend to get is that deviation from that twenty-eight-day cycle is not a good thing. What I learned from the evolutionary lens of biological anthropology is that this variation is adaptive, that when we vary from this false norm – really an extreme that does not reflect the physiology of most women of the world – and can identify lifestyle or environmental factors producing this variation, that it means our bodies are working properly. It would not make sense for our bodies to produce cycles capable of conception all the time, if we don’t always have the attention, energy or resources to support a baby. And even if we have other reasons to not want a child that wouldn’t influence our bodies, like our jobs or our preferences, constant ovulatory cycling exposes our bodies to doses of hormones that can increase our risk of reproductive cancers [8, 9].

I’m not asking every woman to embrace painful periods, cycles so long as to make you wonder every few months if you’re pregnant, or symptoms that significantly interfere with her quality of life: I know some women are derailed by pain, discomfort or other symptoms and find regulating their cycle helps, and at a few points in my life I have too. But I am asking that we use a different frame to understand and describe our bodies. If responding to our environment is adaptive, then variation is adaptive, and variation is the real norm. The better we understand how our lifestyle and environment impact our cycles, the better we can forgive a little variation, and thank our bodies for knowing what to do, sometimes better than we do.

References:

1. Bentley, G.R., A.M. Harrigan, and P.T. Ellison, Dietary composition and ovarian function among Lese horticulturalist women of the Ituri forest, Democratic Republic of Congo. Eur J Clin Nutr, 1998. 52(4): p. 261-270.

2. Warren, M.P. and N.E. Perlroth, Hormones and sport: the effects of intense exercise on the female reproductive system. Journal of endocrinology, 2001. 170: p. 3-11.

3. Lager, C. and P.T. Ellison, Effect of moderate weight-loss on ovarian function assessed by salivary progesterone measurements. Am J Hum Biol, 1990. 2(3): p. 303-312.

4. De Souza, M.J., Menstrual disturbances in athletes: a focus on luteal phase defects. Medicine & Science in Sports & Exercise, 2003. 35(9): p. 1553-1563.

5. Allsworth, J., et al., The influence of stress on the menstrual cycle among newly incarcerated women. Women’s Health Issues, 2007. 17(4): p. 202-209.

6. Clancy, K.B.H., et al., Endometrial thickness is not independent of luteal phase day in a rural Polish population. Anthro Sci, 2009.

7. Jasienska, G. and P.T. Ellison, Physical work causes suppression of ovarian function in women. Proceedings of the Royal Society of London Series B, 1998. 265(1408): p. 1847-1851.

8. Jasienska, G. and I. Thune, Lifestyle, hormones, and risk of breast cancer. British Medical Journal, 2001. 322: p. 586-587.

9. Strassmann, B.I., Menstrual cycling and breast cancer: An evolutionary perspective. Journal of Womens Health, 1999. 8(2): p. 193-202.

About the Author: Kate Clancy is an Assistant Professor of Anthropology at the University of Illinois, Urbana-Champaign. Her work is on evolutionary medicine, and the intersection of endometrial functioning, stress and inflammation. Kate blogs at Context and Variation and her Twitter handle is @KateClancy. She has a daughter, two cats, and has been promised a dog. These days her cycle is anywhere from twenty seven to forty days long.

 

The views expressed are those of the author and are not necessarily those of Scientific American.



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Comments 17 Comments

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  1. 1. Bill Case 10:54 am 12/23/2010

    Just wondering? I have thought that the ‘break down in sexual morality’ in the western world is not a result of cultural shifts, but is the result of biological shifts brought on by the presence of ‘plenty’ in modern society. That the increase in ‘porn’ is not a result of moral laxity but a response to a heighten sexual urgency and demand.

    This article hints that such a shift can take place.

    Link to this
  2. 2. basudeba 7:27 pm 12/23/2010

    It is true that the twenty-eight-day cycle is adaptive, but it is also true that deviation from that is not a good thing. If you maintain the life style of your mother, it would be similar to your mother’s cycles. There is a correlation between the phase of moon at the time of your birth and the phase of moon during the 28th day. There are specific alignments between these two phases for the menstrual cycle to occur. In case the alignment is not right, the cycle gets advanced or postponed till the right alignment.

    We have checked it innumerable times and found it true.

    basudeba.

    Link to this
  3. 3. kclancy 8:06 pm 12/23/2010

    Bill, thanks so much for commenting. I’m not sure what you mean by a breakdown in sexual morality, though — are you speaking of promiscuity? Because that’s not a new thing at all, and in fact occurs at least as much in contemporary forager populations as it does in more industrialized populations like the US.

    I wonder if what you are getting at is the relationship between libido and hormone concentrations. That doesn’t appear to be a one-to-one correlation, and I would suspect that those relationships are also relative to norms in one’s population (meaning a population with low levels will not be low libido, but instead the variation within that population may loosely correspond).

    basudeba, thanks also for writing, but I have to disagree with you pretty firmly. The evidence for a relationship between the menstrual cycle and the lunar cycle has been disproven many times over.

    Link to this
  4. 4. E-boy 4:19 am 12/24/2010

    Lovely article. I particularly like that you point up this cultural expection we have in the states compared to known evidence both learned through your studies and then perhaps brought home even more solidly by direct field observation.

    A lot of "common Knowledge" these days just isn’t an accurate representation of what scientists really know. Another example would be what is taught about native americans in high school as opposed to the knowledge they’ve accumulated through studies over the last several decades that hasn’t percolated down to high school text books yet.

    I really enjoy any and all information about the stuff that makes people, people and your article was informative and interesting. More please. :-)

    Link to this
  5. 5. femion 9:42 am 12/24/2010

    I don’t really understand the point of this article. Sure, there are many states of the female reproductive system that can be considered "natural" or "normal", but why should we aim for these? The "normal" state for most women for most of history until recent decades was to be constantly pregnant or nursing, or so malnourished that they couldn’t get periods, and repeat this cycle until dying in childbirth. Is that really something to aim for? I will take my 28-day oral contraceptive cycle, thank you very much.

    Link to this
  6. 6. Bill Case 9:44 am 12/24/2010

    kclancy: "I’m not sure what you mean by a breakdown in sexual morality, though — are you speaking of promiscuity?" Not particularly, I suppose I was being over sensitive to the American Conservative views of what they may call "moral breakdown". More explicitily, I meant the increase in sexual signalling in advertising, in entertainment, in literature; the increase in poronography; the increase in promiscuity. It just seems to me that they have things backwards. This more highly sexualized society is not a result of a cultural shift away from Victorian values and a ‘break down in morality’ but is the result in a physical change (probably hormonal) in men and women that has increased the demand for a more sexually explicit society.

    I put the above forward as a hypothises, and was asking if there is a chance that it is true or at least partially true?

    One example of what I mean. The large number of teenage pregancies, in the modern age of birth control seems unexplainable if sexual activity in the young is being engaged in purely for its entertainment value. It seems to me that there is some underlying drive to procreate at a young age that is overriding all cultural and practical norms to the contrary.

    Link to this
  7. 7. Bill Case 10:11 am 12/24/2010

    kclancy: In case I failed to make my point, your article seemed to confirm that that, yes, there is an environmental component involved in the receptivity of females to sex.

    Link to this
  8. 8. kclancy 10:24 am 12/24/2010

    E-boy, thanks so much!

    femion, thanks for writing. The point of the article was to acknowledge these many states of "normal," and try to be a bit more forgiving of natural variation, rather than always seek to control it. What you bring up about pregnancy and nursing is right, but would be fodder for a whole new post! I wanted to keep this one short to keep it readable. And, if hormonal contraceptives are working for you that’s totally fine. Again, the idea was to promote a more understanding view of our bodies, rather than a rigid one that demands our bodies operate one way or another (so contraceptives are awesome for some women, not so much for others).

    Bill, I do have a better sense of what you’re saying now, thanks for clarifying. Though, to be honest, teenage pregnancies aren’t that new in our evolutionary history either! Plenty of women probably had an age at first birth around nineteen or so; the difference is that they likely didn’t start cycling until sixteen or seventeen years of age. These days we have lots and lots of years between our first cycle (menarche) and our first birth (depending on the population, anywhere from the teens to the mid-twenties or later). Sexual explicitness also seems to vary greatly from culture to culture, if my weak memory of Shostak’s book Nisa and other books I had to read as a college student are an indication. I’m not saying you’re not right about the increase in explicitness or teen pregnancy, I’m just wondering if cultural change explains this better than hormones. But hey, it’s testable so we can hope someone takes on your idea!

    And I like the point you made in your last clarification: environment does impact female receptivity, yes.

    Link to this
  9. 9. jcason 5:33 pm 12/24/2010

    Thank you for an informative article. I had never gotten the same sense in my growing up that deviation was a bad thing, but I didn’t get much information either. It wasn’t until I visited a midwife during pregnancy that I really began to get in touch with my body and how it worked. After that point, I could tell which phase of my cycle I was in simply by tuning into a number of sensations. While breastfeeding on demand, I did not resume menstruation for 18 months. When I visited Planned Parenthood to discuss birth control options during this time, I was treated as if there was something wrong with my body. However, my regular attendance at La Leche League meetings let me know that my variation was perfectly normal.

    I remain struck to this day how little women seem to know about their cycle and how little credit health/medical providers give women for being an important knowledge resource as inhabitants of their own bodies. I had a doctor once inform me that giving birth in a squatting position could be dangerous and that I would need to find a new doctor (he couldn’t compromise safety) if I insisted on birthing in such a position. My position was simply that I wanted to birth in whatever position felt right at the time, and I could not know that until I was already laboring. But variation from the script is undesirable to some physicians who specialize in reproductive medicine, and they actively discourage women from listening to what their bodies will tell them.

    Sorry for the ramble. I found your article intriguing.

    Link to this
  10. 10. raphaelf 7:04 pm 12/24/2010

    Thank you for this article. As a physician, I encounter female patients who occasionally ask me regarding their "irregular" menstrual periods and I suppose that much of what I see is based on the fact that a woman should have a regular menstrual period of every month. I am not able to see from the other perspective, that is, from the woman’s body’s point of view . A little bit more inquiry as to her lifestyle would suffice enough to decide if she really has an organic problem and needs medical intervention or she simply needs to change her lifestyle. I would now rather think that a "regular" menstrual cycle is just like a person’s "regular" bowel habit – some people do it frequently (like daily), some do not (like every other day)- just simply asking some salient questions would lead us to decide if we need to intervene or not.

    Link to this
  11. 11. basudeba 8:43 am 12/25/2010

    You say: The evidence for a relationship between the menstrual cycle and the lunar cycle has been disproven many times over. But what were the Researchers looking for in those experiments. We never stated it is a straight forward relationship. We said there are specific alignments between these two phases for the menstrual cycle to occur. Are the Researchers aware of which alignment we were talking about? Or once they say something it is the Gospel truth and the whole truth. Sorry, we beg to differ on hard evidence. We have experimented it and found our statement true.

    basudeba.

    Link to this
  12. 12. dianegrace 6:19 pm 12/27/2010

    Good article; I appreciate the growing attention to these issues. Ms. Clancy, have you done any research on the "new" trend of continuous birth control? A lot of people think it’s unnatural for a woman not to have her period, but quite frankly, I couldn’t be happier having such control over my body. As far as I know, it’s not harmful, and some studies even suggest it is healthy.

    Link to this
  13. 13. Norwin 5:36 pm 01/1/2011

    Well, what an informtive article. Now, from a mathematical viewpoint, NORMAL does not mean RIGHT or CORRECT. It simply means the EXPECTED under certain conditions.

    If you toss a coin a hundred times, you expect 50 heads and 50 tails. But you might not get this result in your earthly life span, and this is no indication of malfunction in the system.

    For each girl, from the menarche, the body would be adjusting its cycle as it interacts with both the internal and external environments until it achieves its equilibrium – ITS OWN regular cycle. This may take months, years, or forever, depending on the ever changing environmental factors. And it is NORMAL for the individual regular cycle to deviate significantly from the average village, city, state, or world regular cycles, which are usually outdated anyway. This is no indication of a medical problem unless there are other collaborative indicators.

    Link to this
  14. 14. Norwin 5:47 pm 01/1/2011

    Well, what an informtive article. Now, from a mathematical viewpoint, NORMAL does not mean RIGHT or CORRECT. It simply means the EXPECTED under certain conditions.

    If you toss a coin a hundred times, you expect 50 heads and 50 tails. But you might not get this result in your earthly life span, and this is no indication of malfunction in the system.

    For each girl, from the menarche, the body would be adjusting its cycle as it interacts with both the internal and external environments until it achieves its equilibrium – ITS OWN regular cycle. This may take months, years, or forever, depending on the ever changing environmental factors. And it is NORMAL for the individual regular cycle to deviate significantly from the average village, city, state, or world regular cycles, which are usually outdated anyway. This is no indication of a medical problem unless there are other collaborative indicators.

    Link to this
  15. 15. kclancy 9:39 am 01/3/2011

    Thanks everyone for your comments. I’m so glad you found this useful. Jcason, I totally hear you; I went 12 months without a cycle while breastfeeding, and it was pretty intermittent for the year after that — plenty of research has shown that these long periods of amenorrhea are to be expected in many women. Rafaelf, you make such nice points — women have been trained for so long to think they’re abnormal that they come to the doctor at the first sign of irregularity. There is a chance here for the doctor to help the patient understand how normal she actually is, if her lifestyle is producing her variation.

    Dianegrace, I haven’t done any research on continuous oral contraceptive use myself, but I find the topic fascinating. Perhaps one day I’ll get to focus my attention on this. And Norwin, yes, exactly! The popular understanding of normal, versus say the mathematical or statistical one, is very different. You’ve probably identified another place where the communication of what is normal has broken down for women.

    Thanks again, everyone!

    Link to this
  16. 16. PDerry 11:51 am 01/3/2011

    My husband (a physicist) and I (a health psychologist who studies menstruation) recently published the results of our study of chaos theory and the menstrual cycle (http://www.nonlinearbiomedphys.com/content/4/1/5). Chaos theory is about systems that generate outcomes that appear random but aren’t. While many systems studied by scientists have outcomes that are predictable and regular, chaotic systems are by definition organized and deterministic but the outcomes are by their nature variable and unpredictable. Our research provided evidence that variability in the number of days between one menstrual cycle and the next (which is common) is the outcome of this type of system. In other words, even without adaptation to the environment and lifestyle, a certain amount of variability is natural just due to how the system works. Some theorists believe that chaotic systems are better able to adapt to changing conditions.

    Link to this
  17. 17. kclancy 4:51 pm 01/7/2011

    PDerry, that is so cool. Checking out your paper now.

    Link to this

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