Tuesday, August 2nd 2011
Your vaguely suggestive image of chestnuts for the day.
In high school, I enjoyed participating in the science fair. I chose fairly random topics each year, but I do remember the year I studied the pH of soil and its impact on the color of flower petals. I grew a small set of African violets for a few weeks, then ground up their petals and subjected them to a spectrophotometer. Of course, with the small changes I made to the soil and short amount of time I changed the soil pH, I found no differences in petal color, but I felt like a Real Scientist.
What I do these days is Real Science, of course, but no one told me you could study hormones and the uterus and call it Science when I was in high school. So when I asked around about how I could contribute to Scientific American’s Chemistry Day, and someone suggested I look into vaginal pH and its impact on yeast infections, my interest was piqued.
You probably know that pH is how you measure how acid or basic a solution is. And you may even remember that water is considered neutral, at a pH of about 7 along the 0 to 14 pH scale. But did anyone tell you that the vagina is acidic?
Healthy, premenopausal vaginal pH tends to range from about 3.8-4.5. (However, this may be a bit US or Euro-centric. A topic for a whole other blog post would be to examine global variation in pH: I found an article on Indonesian women that suggests a slightly higher average: Ocviyanti et al 2010.) Having an acidic vagina is a good thing, because it makes the vaginal and uterine environment less hospitable to bacteria and other foreign bodies. When the vagina is a bit more basic, say around 5 and up, it seems to be more susceptible to bacterial infections and yeast overgrowth.
A few things impact vaginal pH. First, it appears to correlate inversely with estradiol concentrations. Estradiol is the hormone that increases through the first half of the cycle and peaks at ovulation. This means estradiol is rather low from the premenstrual phase, through menses and the first week or so of the next cycle. So the vagina becomes a bit more basic during this time, as well as through perimenopause and menopause. In fact by menopause, vaginal pH nears neutral (Caillouette et al 1997).
As you might expect, putting things into your vagina with a higher pH can increase its pH as well. This is where unprotected heterosexual sex and douching come in. Semen is very slightly basic, with a pH of healthy ejaculate around 7.2-7.8. This means an acidic vaginal environment could be inhospitable to semen, but also that semen could increase vaginal pH.
To douche is to cleanse the vagina, usually with a stream of liquid. There are now also wipes available. Some, but not all, data suggest African-American women have different attitudes about douching than Caucasian women, and douche more frequently (Hansen Cottrell 2006).
Yet aside from its use as an insult (or, in the case of my roller derby team, a battle cry when a particular jammer is up), the term douche probably didn’t make it into regular conversation that often… until recently. Summer’s Eve, a brand of feminine cleaning products that includes douches and wipes, has gotten into some trouble with their most recent advertising campaign. Their talking hand ads portray racial stereotypes (and have since been pulled), and their historical ad, in the words of a recent feministing commenter, help remind women that to many we are just “a vagina with legs.”
With these videos, young and old alike (the extended version of the “historical” one played at the opening of Harry Potter) now have the impression that douching and feminine wipes are a way to show your vagina some love.
They are not.
A quick Google search turns up several reputable websites with good medical information, all of which recommend against douching. A quick Google Scholar search reveals empirical science articles that demonstrate at least two main reasons douching is unhealthy. First, many douching products are more basic than a healthy premenopausal vagina. Second, douching products and feminine wipes contain fragrance, which can irritate the sensitive skin of the labia, vulva and vagina.
Both of these issues serve to disrupt normal vaginal flora. And when you disrupt the normal flora, the benign bacteria who live in your body all the time and whose presence tends to outcompete the bad stuff, you get more of the bad stuff. This can lead to an increased risk of bacterial vaginosis (Brotman et al 2008, Holzman et al 2001) and yeast infections, and BV in particular can increase the risk of pre-term birth (Hillier et al 1995).
Now, some douche products claim to be pH-balanced, and Summer’s Eve is one of them. But I cannot find for the life of me what that actual pH is. Is it pH-balanced to skin (around 5.5)? Is it pH-balanced in that it is neutral (7)? Both of those would indicate that it is too alkaline for the vagina.
But even if we assume that feminine cleansing products are at a low enough pH to not disrupt the vagina’s acidity, you still have fragrance. And not only are a significant number of people now allergic to the main fragrances used in consumer products (Buckley et al 2001), fragrances can be inherently irritating to the skin around the genitals in those who aren’t allergic. Allergic reactions to fragrance can initiate or worsen vulvar disease (Margesson 2004).
Let your vagina clean itself. It is acidic for a reason, and no, it’s not supposed to smell like a flower. It’s supposed to smell like a vagina.
References
Brotman, R., Klebanoff, M., Nansel, T., Andrews, W., Schwebke, J., Zhang, J., Yu, K., Zenilman, J., & Scharfstein, D. (2008). A Longitudinal Study of Vaginal Douching and Bacterial Vaginosis–A Marginal Structural Modeling Analysis American Journal of Epidemiology, 168 (2), 188-196 DOI: 10.1093/aje/kwn103
Buckley, D., Wakelin, S., Seed, P., Holloway, D., Rycroft, R., White, I., & McFadden, J. (2000). The frequency of fragrance allergy in a patch-test population over a 17-year period British Journal of Dermatology, 142 (2), 279-283 DOI: 10.1046/j.1365-2133.2000.03298.x
Caillouette JC, Sharp CF Jr, Zimmerman GJ, & Roy S (1997). Vaginal pH as a marker for bacterial pathogens and menopausal status. American journal of obstetrics and gynecology, 176 (6) PMID: 9215184
Cottrell, B. (2003). Vaginal Douching Journal of Obstetric, Gynecologic, and Neonatal Nursing, 32 (1), 12-18 DOI: 10.1177/0884217502239796
Hillier, S., Nugent, R., Eschenbach, D., Krohn, M., Gibbs, R., Martin, D., Cotch, M., Edelman, R., Pastorek, J., Rao, A., McNellis, D., Regan, J., Carey, J., & Klebanoff, M. (1995). Association between Bacterial Vaginosis and Preterm Delivery of a Low-Birth-Weight Infant New England Journal of Medicine, 333 (26), 1737-1742 DOI: 10.1056/NEJM199512283332604
Holzman, C., Leventhal, J., Qiu, H., Jones, N., & Wang, J. (2001). Factors Linked to Bacterial Vaginosis in Nonpregnant Women American Journal of Public Health, 91 (10), 1664-1670 DOI: 10.2105/AJPH.91.10.1664
Margesson, L. (2004). Contact dermatitis of the vulva Dermatologic Therapy, 17 (1), 20-27 DOI: 10.1111/j.1396-0296.2004.04003.x
Ocviyanti, D, Rosana, Y, Arifin, Z, & Darmawan, F (2010). Effect of contraception on vaginal acidity among Indonesian women Indonesian Journal of Obstetrics and Gynecology, 34 (2), 69-72
Wednesday, July 27th 2011
I am away on vacation this week. I have decided to share my most popular post to date with the Scientific American audience, in the hopes of getting a few more people excited about physiology, women’s health, and culture. Enjoy!
When I was thirteen years old, I got my period. Soon after, I remember going with my mother to the nurse practitioner’s office — her name was Debbie. Debbie told me that once girls got their periods, they were more likely to be anemic, and I would have to watch out for it. She suggested I start to take an iron supplement.
Something about that conversation irked me, even when I discovered that I was slightly anemic a few years later. I disliked the implication that one could be pathological just by being female. And I didn’t understand how it was that menses, which is only about thirty milliliters of blood loss per menses, could have such a profound impact on women’s iron status.
When I was in college, I studied this in a bit more depth in my undergraduate thesis. I discovered two important studies:
First, most people assume that the sex difference in iron stores in males and females, which begins at puberty, is due to the onset of the period and looks like this:
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| Figure 1. Made-up data to visually represent the assumed way the sex difference in hemoglobin is produced. No, I can’t find real data in the literature but yes, if you find any send it along and I’ll update the post. |
However, the sex difference in iron status in males and females derives from an increase in male iron stores at puberty, not a decrease in female iron stores. This has to do with oxygen transport and testosterone (Bergstrom et al 1995). This means that the difference that occurs at puberty actually looks like this:
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| Figure 2. Made-up data to visually represent the actual way the sex difference in hemoglobin is produced. See caveat from Figure 1. |
Second, the main culprit for iron-deficiency anemia (IDA) in men is upper-gastrointestinal bleeding, so when men present with IDA the first thing they do is an endoscopy. When women present with IDA they give her iron supplements and tell her to go home because it’s just her ladybusiness. Kepczyk et al (1999) decided to actually do endoscopies on women for whom a gynecological source was diagnosed by a specialist for their IDA. They found a whopping eighty-six percent of these women had a gastrointestinal disease that was likely causing their IDA. Therefore, menses likely had nothing to do with their IDA, and the assumption that menses made them pathological actually obstructed a correct diagnosis.
The majority of the women in that study were bleeding internally, and no one had figured it out until then because they had periods.
When I went to graduate school, I wanted to study menstrual and endometrial functioning because the assumption that it inherently causes disease seems to lead to a life of frustration with the medical system for many women. I figured it would be good for us to better understand variation in this part of the body… so that’s what I did. I went to rural Poland, where my colleague Dr. Grazyna Jasienska has a lovely field site perfect for testing my questions about the endometrium: I wanted a non-industrial population, but couldn’t choose one so remote that I didn’t have access to a hospital, since the women would need to do ultrasounds for me to image their endometria. Then, I didn’t set out to test specific questions about IDA, but Dr. Jasienska wanted to do some blood tests on my subjects for a related study, and happened to do a full work-up on them.
Without meaning to, I ended up with two very useful pieces of evidence: measurements of their endometrial thickness, and their iron status. I also knew their dietary iron intake since I did 24-hour diet recalls. I realized that I had the evidence in front of me to test the relationship between menstruation and anemia directly, rather than indirectly like other studies I had read.
It was a matter of some simple correlations (Clancy et al 2006):
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| Figure 3. Red blood cells (RBC) and hemoglobin (Hg) are positively correlated with endometrial thickness (from Clancy et al 2006). Click to embiggen! |
Take a look at the p-values for the relationship between endometrial thickness (ET) and red blood cells (RBC), and ET and hemoglobin (Hg): both are statistically significant. What’s more, the relationships are positive. That means that the thicker the endometria, the better the iron status. I’ll admit, when I ran these stats my hypothesis was simply that there would be no relationship, likely meaning that the effect of ET on iron status was at most neutral. But a positive effect? At least in this test, there is no support for the prevailing medical assumption that menses is correlated with IDA.
I was reminded of this study of mine recently, because it was cited by someone else studying something a bit different (vanity Google Scholaring will get you that). Elizabeth Miller at the University of Michigan wrote a very interesting paper on maternal hemoglobin depletion, which is the situation where pregnancy and lactation deplete iron stores. Miller (2010) studied this phenomenon in two populations in northern Kenya, a settled population and a more pastoral one, as a way to understand the differential impact of interbirth interval, energetic constraint, and dietary iron intake on maternal depletion. I’m going to focus just on the part of this study related to issues of menses and IDA.
Miller found that iron stores slowly increase in lactating mothers with months since birth, but also that the more children these women had, the lower their hemoglobin. This makes sense in terms of where iron needs to be allocated during pregnancy and lactation, and how women with many children might not have enough time or resource to replete their iron before having their next kid.
But the really cool finding, to me, was that resumption of menses after pregnancy was positively associated with hemoglobin. Resumption of periods after pregnancy is highly variable, and largely dependent on energy availability and lactation practices. These results, that iron stores increase once you start getting your period again, indicate again that menses is not having a negative effect on iron stores. So this is the second study I know of to show a positive relationship between menses and iron status.
Ladies, unless you are menorrhagic (bleeding more than 120 milliliters each cycle) your period is not doing you wrong. If you have iron-deficiency anemia and your doctor is insisting it’s because you slough off your endometrium from time to time without doing a single test to confirm it, you may want to insist on an endoscopy. It could save your life.
References
Bergström E, Hernell O, Persson LA, & Vessby B (1995). Serum lipid values in adolescents are related to family history, infant feeding, and physical growth. Atherosclerosis, 117 (1), 1-13 PMID: 8546746
Clancy, K., Nenko, I., & Jasienska, G. (2006). Menstruation does not cause anemia: Endometrial thickness correlates positively with erythrocyte count and hemoglobin concentration in premenopausal women American Journal of Human Biology, 18 (5), 710-713 DOI: 10.1002/ajhb.20538
Kepczyk, M. (1999). A prospective, multidisciplinary evaluation of premenopausal women with iron-deficiency anemia The American Journal of Gastroenterology, 94 (1), 109-115 DOI: 10.1016/S0002-9270(98)00661-3
Miller EM (2010). Maternal hemoglobin depletion in a settled northern Kenyan pastoral population. American journal of human biology : the official journal of the Human Biology Council, 22 (6), 768-74 PMID: 20721981
