By: Jennifer Abbasi, LiveScience Contributor
Published: 12/12/2012 11:38 AM EST on LiveScience
Men find women more attractive near ovulation, when they're most fertile, suggests the largest study yet to look at whether a gal's allure changes over the course of her menstrual cycle.
The findings are plausible, the scientists note, since the ratings of attractiveness were related to hormonal shifts, which may cause facial and vocal changes in women.
The research, detailed online Nov. 15 in the journal Hormones and Behavior, adds to the idea that a women's cycle is linked with various physiological and behavioral changes. For instance, earlier studies have found that when fertile, women's sexual desire increases, as does their preference for strong-jawed men. Past studies have also shown men find fertile ladies' dance moves more attractive, as well as her voice and smell, with one well-known 2007 study showing erotic dancers brought in better tips during the fertile phase of their cycle.
In the new study, researchers took photographs of 202 women's faces and made recordings of their speaking voices at two points in their menstrual cycles. They also took saliva samples to measure hormone levels during both sampling sessions. More than 500 men rated the attractiveness of the women's faces and voices from one of the two sessions. The ratings from the first session were averaged for each woman and then compared with ratings for her second session.
Men rated faces and voices as more attractive when women's progesterone levels were low and estradiol (estrogen) levels were high.
"The only time in the cycle when estradiol levels are high and progesterone levels are simultaneously low is the late follicular phase, near ovulation when fertility is highest," said the study's lead author David Puts, an assistant professor of anthropology at Pennsylvania State University. [10 Odd Facts About a Woman's Body]
A group of more than 500 women were also asked to rate women's attractiveness across their cycles. (The two groups of women did not overlap.) They scored the photographs and vocal recordings based on two measures: flirtatiousness and attractiveness to men. Women rated the subjects higher on both measures when the subjects were in their more fertile phase.
"We learned beyond a reasonable doubt that women's faces and voices change over the menstrual cycle, and that both men and women perceive this as changes in attractiveness," Puts told LiveScience.
Nathan Pipitone, a psychologist at Adams State University in Colorado who studies human mating and voice attractiveness, agreed: "This paper establishes conclusive evidence for how men and women rate other women as a function of their hormonal status." Pipitone, who was not involved in the research, said the study's large sample size and measure of hormone levels strengthen its conclusions.
Hormones and sexiness
Research has suggested hormones, indeed, alter facial and vocal features.
The larynx, or voice box, has estrogen and progesterone receptors, and puberty, pregnancy, menopause, hormone replacement therapy and hormonal contraceptive use have all been shown to change women's voices, the study authors said. A 2011 study co-authored by Pipitone found that men could predict when women were menstruating based on vocal features, such as its mood, pitch and quality. [7 Surprising Facts About the Pill]
In the new study, women's hormonal state was linked with the perception of attractiveness, but no acoustic changes were found. "In evolutionary terms, it's the perception of attractiveness that matters to humans, not the proximate mechanisms (i.e., acoustics) that allow us to try and quantify what is and what is not an attractive voice," he wrote in an email.
Puts is studying facial changes over a woman's cycle that could make her appear more or less attractive. "There could be changes in blood flow that would result in color changes in the face, changes in acne, or changes in puffiness due to water retention," he said.
Most scientists believe such cyclic changes, known as fertility cues, are "leaked," meaning they are a byproduct of female reproductive biology rather than traits that evolved to advertise fertility. Unlike female chimps and other mammals, women conceal their ovulation, giving them more control over their reproduction. "Many researchers favor the hypothesis that concealing ovulation afforded our female ancestors the ability to cheat on their mates, because their mates couldn't concentrate mate guarding near ovulation if they couldn't tell when it occurred," Puts said.
Men who could pick up on women's subtle fertility cues, even if they were unaware of it, may have had more reproductive success. The same could be true for women, researchers theorize: Women who were able to subconsciously spot a fertile rival might have better guarded their mates from them, keeping their partner's investment focused on them and their children.
Researchers from the University of Missouri and the University of Sterling in Scotland also contributed to the study.
- Busted! 6 Gender Myths in the Bedroom & Beyond
- 50 Sultry Facts About Sex
- 5 Myths About Fertility Treatments
1. Your fertility is mostly determined by genetics, which influences how many eggs you are born with. Doctors believe that the number of eggs you have at birth determines the length of time you will remain fertile. At birth, women have about two million eggs in their ovaries. For every egg ovulated during your reproductive life, about 1,000 eggs undergo programmed cell death. Other things, such as smoking cigarettes and certain types of chemotherapy, can accelerate egg cell death and promote an earlier menopause.
2. Regular menstrual cycles are a sign of regular ovulation. Most women have regular cycles lasting between 24 and 35 days. This is usually a sign of regular, predictable ovulation. Women who do not ovulate regularly have irregular menstrual cycles. Those who do not ovulate at all may have a genetic condition called polycystic ovarian syndrome (PCOS).
3. Basal temperature charting does not predict ovulation. An older method of tracking ovulation involves taking your oral body temperature each morning before getting out of bed. This is called basal body temperature. This method is used to spot a rise in basal temperature, which is a sign that progesterone is being produced. The main problem with using this method is that your temperature rises after ovulation has already occurred. This makes it more difficult to time intercourse at an optimal time for conception. A better method is to use over-the-counter urine ovulation predictor test kits such as Clearblue Easy. These kits test for the hormone that prompts ovulation, which is called luteinizing hormone (LH).
4. Most women with blocked fallopian tubes are completely unaware they may have had a prior pelvic infection. About 10 percent of infertility cases are due to tubal disease, either complete blockage or pelvic scarring causing tubal malfunction. One major cause of tubal disease is a prior pelvic infection from a sexually transmitted disease such as chlamydia. These infections can cause so few symptoms that you may be completely unaware your tubes are affected. This is why fertility physicians will order a dye test of the tubes, called a hysterosalpingogram (HSG), if you have been trying and failing to conceive for 6 months or longer.
5. In most cases, stress does not cause infertility. Except in rare cases of extreme physical or emotional distress, women will keep ovulating regularly. Conceiving while on vacation is likely less about relaxation than about coincidence and good timing of sex.
6. By age 44, most women are infertile, even if they are still ovulating regularly. Even with significant fertility treatment, rates of conception are very low after age 43. Most women who conceive in their mid-40's with fertility treatment are using donated eggs from younger women.
7. Having fathered a pregnancy in the past does not guarantee fertility. Sperm counts can change quite a bit with time, so never assume that a prior pregnancy guarantees fertile sperm. Obtaining a semen analysis is the only way to be sure the sperm are still healthy!
8. For the most part, diet has little or nothing to do with fertility. Despite popular press, there is little scientific data showing that a particular diet or food promotes fertility. One limited study did suggest a Mediterranean diet with olive oil, fish and legumes may help promote fertility.
9. Vitamin D may improve results of fertility treatments. A recent study from the University of Southern California suggested that women who were undergoing fertility treatments, but had low vitamin D levels, might have lower rates of conception. This vitamin is also essential during pregnancy. At Pacific Fertility Center, we recommend our patients take 2,000-4,000 IU per day.
10. Being either underweight or overweight is clearly linked with lowered levels of fertility. The evidence in recent years is that obesity is clearly linked with a longer time to conception. Having a body mass index less than 18 or over 32 is associated with problems ovulating and conceiving, as well as problems during pregnancy.