Love's Chemistry and the Pill: are they at odds?

Love's Chemistry and the Pill: are they at odds?

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Love’s Chemistry and the Pill: are they at odds?

By Abigail Jeffies

When we fall in love, there is mystery, excitement, romance, obsession, anxiety, anticipation, and suspense—to name but

of few of love’s many undeniable, though unscientific, manifestations. But when we are lucky enough to find a mate who loves us

back, we say there is chemistry.

Though humans have long lived by this truth, scientists are only just beginning

to uncover the actual mechanisms that drive the mating game. One surprise: the

use of oral contraceptives may throw a wrench into them.

The scent of attraction

Fertility cues in men (deep voice, athletic physique, and take-charge, hunky kind of

dominance) and women (feminine face, curvy figure, and alluring voice) are just plain

sexy, but they also tell us on a subliminal level that if we mate with this person, we are

more likely to have strong, healthy off spring. There may also be invisible cues that tell

us when a biologically fit or fertile potential mate is at hand. Pheromones, chemical

signals that trigger a natural response in another member of the same species, may

attract humans to one another sexually through smell.

“There are millions of things that are going on with different chemicals that we perceive

and don’t perceive,” said Chris Kilham, Explorer in Residence at the University of

Massachusetts, Amherst, and author of Hot Plants: Nature’s Proven Sex Boosters for

Men and Women. “So much has to do with the invisible. We have all kinds of

mechanisms that we probably haven’t figured out yet that relate to the sense of smell,

and they have a great deal to do with biological attraction.” Studies have found

numerous cause-and effect relationships that indicate body odor can impact

mood, sexual attraction and the release of a hormone that affects the timing of a

woman’s menstrual period. It has also been observed that a woman’s hormonal status can affect her choice of clothing

and the pitch of her voice.

One study found that women prefer the scent of T-shirts worn by men whose

major histocompatibility complex (MHC)—a set of genes that plays an important

role in the immune system—is most dissimilar to their own. Should they mate

with these MHC dissimilar men, they would have a greater chance of producing

off spring with stronger immune systems. “It makes perfect sense that we would

have a mechanism that compels us to mate with someone who is not

MHC-similar, because it’s desirable to avoid inbreeding,” said Alicia Stanton,

MD, Chief Medical Officer of BodyLogicMD and author of Hormone Harmony.

The “divorce” pill?However, the T-shirt odor assessment results were

reversed when the women studied were taking hormone-based oral

contraceptives, suggesting that body scent and hormonal status

influenced mate selection. These women preferred the scent of men who

had MHC similar to their own, as would a relative.

So, does this mean that if a woman is on the pill she might be attracted to

the wrong guy? Or worse: if she’s on the pill when she finds Mr. Right,

then marries him, then stops taking the pill to start a family, will she wake

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up one day and find she’s no longer attracted to him?

“The studies are controversial. The premise that the birth control pill makes women choose their mates less wisely is

not a given,” said Joseph Walsh, MD, Assistant Clinical Professor at the University of Connecticut Health Center in

Farmington. “The trouble with a lot of these studies in evolutionary psychology is that there are associations but no

causation. It’s very difficult to do a randomized study where you have one group on placebo, one group on the pill, have

them choose mates and then reverse it and see what happens with mate selection.”

Does a man read the chemical signals sent by a woman differently when she is taking

the pill? A University of New Mexico study of professional lap dancers found that those

who were not taking hormonal contraceptives earned more money during the most

fertile (ovulating) phase of their menstrual cycles compared to times of low fertility.

Those who were taking hormonal contraceptives (which stops ovulation) did not have

higher mid-cycle earnings, suggesting that men are somehow more attracted to ovulating


The mystery of human pheromones

A popular theory is that pheromones account for chemical sexual attraction.

Pheromones have been found to exist in non-human mammals including

chimpanzees and baboons, but they have not yet been isolated in humans. And

humans may no longer be wired to receive and process pheromones.

The vomeronasal organ, a structure in the nose of many vertebrates that

receives pheromonal messages and sends them to an olfactory region of the

brain, is non-functioning in adult humans.

Though the “how” of the pill’s effect on mate selection is not yet understood, one possible “why” might be based less on

pheromones and more on sociology. Oral contraceptives mimic pregnancy by providing a woman with high levels of the hormones

estrogen and progestin. Th is tricks the ovaries into shutting down egg production, which prevents conception, but it may also

trigger a basic survival strategy. “It has been proposed that women on the pill prefer the scent of a man who is MHC-similar

because pregnant women want to be with someone safe and supportive, such as a relative, while they are vulnerable,” said Mache

Seibel, MD, Reproductive Endocrinologist and Professor at UMass Medical School in Worcester. Mary Jane Minkin, MD, Clinical

Professor of Obstetrics and Gynecology at Yale University School of Medicine in New Haven offered another hypothesis: “The

ovaries make testosterone. Women are sensitive to a lack of testosterone. When the pill causes ovulation to stop this also means that

testosterone production stops, and this might affect libido, thereby causing women on the pill to prefer platonic relationships.” That

said, Minkin noted that libido is “hugely complex” in women. “It’s very different from libido in men for many reasons. My patients

are so terrified of unwanted pregnancy that any loss of libido caused by the pill is compensated for by the sense of protection from

pregnancy. When they’re on the pill, they’re ready for sex,” she said.

The skinny on hormones and birth control

There are several alternative methods of contraception that do not mimic pregnancy.

“Condoms, mechanical methods like diaphragms, the copper-containing intrauterine

device (IUD), and natural family planning prevent pregnancy without using hormones,”

Walsh said. “The progesteronebased IUD secretes hormone but at such a low level that it

would probably not have any effect on mate selection, if this in fact happens.”

Even if a woman is not taking the pill, she may be using a hormone-based birth

control method. “The patch, the NuvaRing, the Depo-Provera 3-month injection,

the single rod implant – these methods are all hormonal, but some of them

contain only half of the hormone that is in the pill,” Walsh said. “In most cases

the pill contains a combination of estrogen and progestin. Implanon and

Depo-Provera contain only the progestin component.

This does reproduce a pregnancy state, but we don’t know what effect this has on mate selection.” The hormones in

contraceptives are not structurally the same as the hormones our bodies make naturally. “Their shapes are not going to fit into the

body’s receptors as well as our own hormones would,”

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Stanton said. “The pill contains progestin (synthetic progesterone), not the natural progesterone that is elevated when a woman is

pregnant, and this difference can cause side effects like weight gain, water retention and depression. This is because progestin

does not act in the body the same way that progesterone does. The body is confused. It thinks there is some

progesterone on board because the pill is affecting some of the progesterone receptors, but not all. The way the pill

appears to disable a woman’s ability to discern MHC may be one of these side effects we don’t yet understand.” Stanton

treats male and female patients with symptoms of hormonal imbalance using bioidentical hormones – soy- and yambased hormones

that have been tweaked in a lab to be molecularly identical to human hormones. “Your body doesn’t know the difference,” she said.

So far, there are no contraceptives available that use bioidentical hormones.

What’s the take-away?

Human pheromones may or may not be imperceptibly advertising fertility, attracting potential mates, or guiding a

pregnant woman to sanctuary among family. They may or may not be turned on and off by synthetic hormones in birth

control pills. Whether there is any link between hormones and pheromones is “the $64,000 question,” Seibel

said. “Almost every woman who has lived in a dorm knows that women who group together menstruate together,”

Seibel said.

“That is believed to be a result of synchronizing pheromones. It’s not a quantum leap to believe that some olfactory

message could attract potential mates.” Not a leap, perhaps, but definitely a stretch. “To put the studies that have been

done into clinical use, to suggest that women not choose the birth control pill in order to avoid the MHC problem, would

be premature,” Walsh said.

At the end of the day, sexual selection is more than hormones and pheromones. “The more people know each other

and care for each other the more these become enhancers rather than selectors,” Seibel said.

Last Updated (Tuesday, 09 March 2010 16:34)

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