This story is really about why females (both laboratory animals and humans) must be properly represented in medical research designed to alleviate pain. But the National Institutes of Health (NIH) primer which generated this article deals specifically with “Sex as a Biological Variable”(SABV).
Why “sex” rather than “gender”? It seems that, until fairly recently, “sex” and “gender” have been used pretty much interchangeably. But the two terms are now developing distinctly divergent definitions.
“Sex” refers to the anatomical and biological differences between the sexes. In today’s lexicon, “gender” is a lot more vague. Its modern usage generally refers to the variations between the societal roles played by women and men.
So after that digression into the dictionary, let’s get back to “Sex as a Biological Variable”. It’s a concept that relates to the practice of pain medicine.
What does “Sex as a Biological Variable” mean?
In 2016, a panel of 13 experts from 9 countries produced a set of guidelines known as Sex and Gender Equity in Research (SAGER). Traditional research recognized only the reproductive anatomical differences between men and women. The multitude of other significant physiological and biological differences between men and women was largely ignored.
In the United States, the NIH addressed this problem. In 2016, it produced an SABV policy that requires researchers to consider sex in the design of both human and animal research projects. These policies reflect the increasing awareness that medical research has generally failed to recognize and control for sex and gender differences in designing studies.
Historically, medical research assumed men and women are generally the same in most respects
So, the common wisdom held, research on men would also apply equally to women. The falsity of this paternalistic assumption has become more and more apparent as significant physiological and biological differences between the sexes have been discovered.
For example, several drugs have been recalled because women suffered severe adverse effects. The testing on those drugs was performed on a population that included insufficient numbers of women.
In 2018, the NIH introduced a new primer on pain research
The new guidelines were presented at the annual scientific meeting of the American Pain Society, held in Anaheim, California. The document explains both why and how SABV must be included in basic, preclinical, and clinical pain research.
The research underlying the NIH primer exposed laboratory testing that over utilized male animals. Little attention was paid to different responses between the sexes. The failure to sort findings into male and female categories resulted in a flawed databank.
Inna Belfer, M.D., PhD, the Program Director of the Basic and Mechanistic Research Branch of the National Institute of Health’s National Center for Complementary and Integrative Health (imagine the size of her business card), was the lead author of the NIH primer.
“A systematic analysis of large databases has revealed that sex and/or gender remain independent and important biological variables that influence disease development and outcomes,” said Dr. Belfer. “Despite this, in preclinical research, including investigations on pain and analgesia, laboratories often use only cells and animals from a single sex to study diseases that affect both men and women.”
Females are underrepresented in the vast majority of pain research studies
Roger Fillingim, PhD, is the director of the University of Florida Pain Research Center and a past president of the American Pain Society. He said, that the NIH primer marks significant and long overdue progress in pain research. “We’ve known for some time, especially in preclinical research, that females are underrepresented in the vast majority of research studies.”
“What’s even more important is that some of the fundamental mechanisms that drive pain differ qualitatively in male and female animals,” Fillingim added. “Let’s say we’ve been hot on the trail of some mechanism and we’re closing in, getting the story all figured out. We develop a drug to target the mechanism, the drug gets to humans, and then the drug fails miserably, because no one bothered to look at the fact that the mechanism may have completely different effects in men versus women.”
“Studying female-dominated pain conditions using male animals sort of adds insult to injury”
“There’s a real disconnect there, Fillingim continued. This has been met with a lot of opposition, because it makes life more complicated in some ways. It does require consideration of statistical issues that investigators may not previously have had to think about, but ultimately it makes better science.”
Women are more likely than men to develop certain pain conditions that afflict both sexes. But we often don’t know why that’s true. We know that several chronic pain disorders occur only in women. But, once again, we don’t know why. That’s why it’s mandatory that pain medicine researchers give full recognition to the vital differences between the sexes. The new SABV standards are now being implemented. When that process is complete, the status of women within the field of pain medicine research will at last be elevated to equality with men.
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