Personal Health

Why Your Race or Gender May Affect How Much Pain You Feel

A new study from Stanford says that pain is neither gender- nor race-neutral.

Pain isn't gender-neutral.

Researchers have long known that women are far more likely than men to develop chronic-pain disorders such as fibromyalgia, irritable bowel syndrome, rheumatoid arthritis and migraines. According to the National Institutes of Health, 80 to 90 percent of fibromyalgia patients are female. According to the US Department of Health and Human Services, severe headaches and migraines are twice as common in women as in men -- 17 percent vs. 7 percent, respectively. HHS also reports that over 12 million American women suffer from chronic pain, at an annual cost of about $13 billion.

Some might argue that women don't feel more pain, they just feel more comfortable than men do about admitting that they hurt. Studies do show that more women than men report chronic pain. But other studies showing higher female than male pain responses among newborns indicate that this is a physiological rather than sociocultural matter. If so, then the better these differences can be understood, the better all patients can be treated for pain.

"Someday there might be a different pain pill for men than for women," says behavioral neuroscientist Jeffrey Mogil, head of the Pain Genetics Lab at Montreal's McGill University. "I know of some pain drugs that work in male mice and not female mice. Whether those drugs will ever be approved for human use is another question."

Studies such as a large-scale new one out of Stanford that's getting lots of buzz show that women have lower pain thresholds than men. Sure, women endure menstrual periods and childbirth. But women are three to six times likelier than men to have chronic-pain conditions such as migraines and fibromyalgia, women suffer significantly more than men do even when both suffer from the same medical conditions, and women require 30 percent more morphine after surgery than men do.

"The differences are real and surprisingly large," Mogil says. "What can explain those differences? It's the answer to all questions: genes and environmental differences."

As for the latter, "Some people have experienced pain more often than others," says Mogil, and/or grew up with certain beliefs about pain, and/or were exposed to physical or sociopsychological phenomena that affected their sensitivities. Scientists have spent the last 20 years "trying to break it down and see if we can come up with specific genes and specific environmental experiences" that determine who suffers how much and why.

Any male-female disparity points to sex hormones. Researchers are investigating these in earnest, having found that women are more sensitive to pain during some parts of their menstrual cycles than others.

Studies on rodents "suggest that the neural circuitry modulating pain is surprisingly different between the sexes," Mogil says. In other words, men and women might be wired differently for pain.

What gets less attention yet is just as fascinating is the fact that pain isn't race-neutral either.

The fact that studies linking pain and race are less numerous than studies linking pain and gender "is a political-correctness thing, not a science thing," Mogil says. "For many years it wasn't a place people wanted to go, because it would be hard to get funding, and a lot of people wouldn't want to admit that these things might be true."

Many studies conducted over the last few decades show that African Americans demonstrate lower pain thresholds and pain tolerance than people from other ethnic backgrounds. In tests gauging physical and verbal responses to pain, African Americans are consistently shown to be more sensitive.

In one study involving the application of tourniquet-like devices, African American participants were able to tolerate the pain for only about half as long as were Caucasian participants. According to the Centers for Disease Control, African American arthritis patients report significantly more severe pain than arthritis patients of other ethnic backgrounds, and nearly twice as much as Asian-Pacific Islander arthritis patients.

"We were doing a study primarily on sex differences and pain and of course, lo and behold, when people bring their gender to the lab they also bring their ethnic background," says pain researcher Roger Fillingim, a behavioral science professor at the University of Florida. His team began investigating race and pain as well -- adding new data acquired with new technology under a more enlightened mindset to a long-established if controversial field.

It's controversial because scientific studies proving physiological differences between people of various ethnic backgrounds contradict the thesis that race is just a social construct. Critics might also argue that such research would only be conducted for racist purposes, and/or that its results might be used in racist contexts.

Has Fillingim been accused of racism for doing this kind of work?

"We encountered some of that thinking as we were publishing our early studies," he recalls, "as if we were somehow trying to promulgate the idea that one race is inferior to another. I can understand those sensitivities, but we do a larger injustice if we ignore the fact that pain is different in some individuals than in others. If ethnic background is associated with the pain experience, then we can use that information to better alleviate pain."

Better late than never, because it has also long been known that African Americans are typically underserved by medical professionals when it comes to pain treatment. A University of California-Riverside study found that African American patients are "considerably less likely" than Caucasians to receive painkillers in American hospitals. This study, whose findings have been confirmed by many others, also noted that when black males are given painkiller prescriptions, they are given smaller prescriptions and fewer drugs than any other type of patient. The study also found that African American males are less likely than any other patients to be advised by medical professionals to take over-the-counter pain medications upon leaving hospitals.

Yet African Americans' higher pain sensitivity has also been indicated in test after test.

One much-cited Harvard-affiliated study, published in 1943, examined the results of pain inflicted via hot lamps applied to participants' foreheads and balloons gradually inflated in their throats. This study found black people to be more sensitive to both types of pain than Northern Europeans, while "Jewish and other Mediterranean races ... had both pain-perception and pain-reaction values which corresponded closely" with African Americans.

"Ethnic differences in pain tolerance are very much like gender differences, although perhaps more politically charged and complicated," says Fillingim, whose recent studies confirm lower pain thresholds and lower pain tolerance among African Americans. "If I talk about sex differences, everybody agrees on who's a man and who's a woman. There are clear biological differences. When you talk about ethnicity, there's no biological smoking gun saying that because these people are African American, they differ from whites. There's no estrogen difference. So what is it?"

Talk about a world of hurt.

Because pain is highly subjective and many studies depend on self-reported pain levels, it has been suggested that people from different ethnic backgrounds don't actually experience different pain levels, but rather express pain differently or apply different coping styles.

"Pervasive mistrust of the medical research community has been documented among African Americans," one study reads, "and it is certainly possible that a less trusting attitude among African Americans might have contributed to greater report of pain."

Such factors might affect gender-related pain studies too: Does society pressure men to act tougher than women and refuse to admit feeling pain?

Recent studies have sought -- and found -- ever more evidence of physiological rather than sociopsychological sources for pain reactions. In one such study, Filllingim's team gauged the muscular reflexes resulting from the painful electrical stimulation of a nerve near the ankle.

"It's not a conscious reflex. You can't control it consciously. It happens too quickly," Fillingim says. "And it required a less intense stimulation for that reflex to occur in African Americans than in whites."

But why?

"Half of the differences in pain response are genetically determined. Half are determined by experiential and psychological factors," he explains. "We want to get a better picture of what drives increased pain and how pain systems function."

That picture could someday lead to highly customized pain treatments rather than one-size-fits-all meds such as morphine and ibuprofen.

"Wouldn't it be best for everyone, and most cost-effective, to pick drugs with the best therapeutic profiles for each patient?" Fillingim asks.

"Let's say somebody you know had to go in for surgery next week. If they're not treated for pain, it will be exquisitely painful. Say everybody gets the exact same drug. But if your acquaintance happens to be a poor metabolizer of that drug or has a genetic background that does not respond favorably to that drug, they could suffer considerably. Or say they have a great genetic background for that drug, but they also have an ethnic background that makes them vomit uncontrollably if they get that drug. Wouldn't it be better to know all this in advance?"

Anneli Rufus is the author of several books, most recently The Scavenger's Manifesto (Tarcher Press, 2009). Read more of Anneli's writings on scavenging at scavenging.wordpress.com.