Autoimmune diseases affect 23.5 million people in the United States. Shockingly, women make up 78% of that statistic . A new theory suggests that the placenta may hold a key to this mystery.
What is an Autoimmune Disease?
An autoimmune disease is a condition when one’s immune system mistakes normal cells for foreign matter and attacks them. For example, Type 1 diabetes is diagnosed when the immune system attacks the pancreas.
Other examples include:
- Systemic lupus erythematosus, which affects the entire body
- Rheumatoid arthritis, which affects the joints
- Psoriasis, which affects the skin cells
- Inflammatory bowel disease, which affects the intestines
- Celiac disease affects the gastrointestinal tract
Health professionals have been unable to determine the exact triggers or reasons behind these false flag immune system attacks .
Why the Placenta is Responsible
Melissa Wilson and her colleagues from Arizona State University published a paper discussing the “pregnancy-compensation hypothesis.” This theory suggests that a woman’s immune system is constantly engaged with the placenta.
Here’s how: Women’s bodies are capable of being pregnant for many years of their adult life. In an old hunter-gatherer setting, well before the popularization of contraceptives, it was common for a woman to bear eight to twelve children. Their bodies evolved to become strong enough for this feat.
As a pregnant woman’s placenta grows, her organs signal the immune system to accept the placenta and fetus, and not eject them like other foreign presences in the body. This lowers the immunity of some women for different periods of time, depending on the person. Too low of an immunity leaves the body vulnerable to pathogens that can harm the fetus. Wilson and her team believe the immune system overcompensates for this in other ways.
However, our times are different from those of the hunter-gatherers. Women tend to have few children today—fewer than two on average in the United States.  Other developed nations have similar numbers.
Wilson believes without the ongoing push-and-pull relationship between the immune system and the placenta—a relationship women’s bodies are evolved to experience—the immune system lacks the suppression during pregnancy and becomes too aggressive. It begins to search for things to attack, even if they don’t put the body at risk. Thus the beginning of every autoimmune disease.
“The immune system was expecting to have exposure to a placenta,” says Wilson. She compares it to a person pulling on something heavy, almost like a slingshot. “If you suddenly don’t have that heavy thing anymore, you’re gonna go off the moon.” 
The Theory of all Theories?
There are many other theories explaining why women have more autoimmune diseases than men. Wilson’s theory seems to encompass many of them and gives an additional explanation involving evolution.
“They were all right,” she says. “But everyone was looking under their own streetlight, and we just waited for it to be daytime.”
The Supporters and Naysayers
So far, no one has attacked Wilson for her theory. In fact, some believe it might be plausible.
“I would say there’s not one theory that explains all [autoimmune diseases],” says Nikolaos Patsopoulos, assistant professor of neurology at Brigham and Women’s Hospital. “This isn’t Lord of the Rings.” 
Still, he admits the following: “This theory puts together a lot of things we know that are true and some that we’re still trying to understand.”
Hal Scofield, a professor of pathology and medicine at the University of Oklahoma, states that the X chromosome contains a lot of genes involved with immunity. Since women have two of these chromosomes while men only have one, they have a double share of these immunity genes. 
This contributes to Wilson’s theory. Woman evolve to produce more genes to contribute to the push-and-pull relationship between the immune system and placenta.
“I don’t think there’s any way out of thinking that placental pregnancy has to have influenced the evolutionary immune system,” Scofield says.
However, not everyone is impressed by Wilson’s theory. Even though it’s an interesting idea, it needs to be tested to be of any value.
David Hafler, a professor of neurology at the Yale School of Medicine, says, “Ideas are cheap. It’s data which is hard to get.” 
Researching the “Pregnancy-Compensation Hypothesis”
Fortunately, there are opportunities to achieve that. Scientists can track the numbers of pregnancies for numerous women and see if it predicts their risk of developing an autoimmune disease. If the theory is correct, women with more pregnancies should have a lower risk.
Alternatively, researchers can track the differences between zoo animals, which are often on a form of contraceptive, or their wild counterparts and see if that dictates any differences in their risk of autoimmune diseases.
A Bright Idea with a Bright Future
The takeaway from this theory is not that women should be pregnant all the time. Pregnancy contains its own risks, and not all women are capable to raise eight to twelve children. A Woman’s desires to have children range, and in this day and age having several of them just isn’t practical for many parents.
The good news is, if the theory holds true, women with their supercharged immune system should have a lower risk of certain diseases. For example, women are proven to be less likely than men to develop nonreproductive cancers. 
Wilson hopes that with further research into the cause of autoimmune disease, they will be treated or prevented with new therapies.
“I’ve never been more excited about an idea than I am about this,” Wilson says. “This is the first time that I can see my work having a direct impact in the next 10 years on human health.”
- Sex Differences in Autoimmune Disease from a Pathological Perspective https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2527069/
- Updated assessment of the prevalence, spectrum and case definition of autoimmune disease https://www.sciencedirect.com/science/article/abs/pii/S1568997212000225?via%3Dihub
- The Pregnancy Pickle: Evolved Immune Compensation Due to Pregnancy Underlies Sex Differences in Human Diseases https://www.cell.com/trends/genetics/fulltext/S0168-9525(19)30079-4
- Is U.S. fertility at an all-time low? Two of three measures point to yes https://www.pewresearch.org/fact-tank/2019/05/22/u-s-fertility-rate-explained/
- Nikolaos Patsopoulos, Ph.D., M.D. https://connects.catalyst.harvard.edu/Profiles/display/Person/45505
- Robert H. “Hal” Scofield, M.D. https://omrf.org/research-faculty/scientists/scofield-robert-h-hal/
- David A. Hafler, MD, FANA https://medicine.yale.edu/neurology/people/david_hafler.profile
- Gender differences in chemical carcinogenesis in National Toxicology Program two-year bioassays https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4778959/
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