Menstrual cramps. Pregnancy. Menopause. Fibromyalgia. Chronic fatigue syndrome. What do they have in common? Women. Of course, the first three are exclusively women's conditions. But, while men can have fibromyalgia (FMS) or chronic fatigue syndrome (CFS or ME/CFS), women develop them at much higher rates.
Why Are Women More Prone to Fibromyalgia & Chronic Fatigue Syndrome?
To find out why, researchers are looking at:
- Brain chemistry
- Immune systems & inflammation
It's also possible that traditional gender roles play a part in the disparity.
When looking gender-based differences, it makes sense to start with hormones. "Hormones, such as estrogen and testosterone, profoundly affect the central nervous system, which is responsible for perceiving and transmitting the sensation of pain," says pain-management specialist Mark Peckman, DO. In addition to FMS and ME/CFS, he says this could help explain why women are more prone to osteoarthritis, headaches and irritable bowel syndrome.
Research suggests that testosterone, the male hormone, plays a role in preventing muscle fatigue. Researchers say a certain protein works with testosterone to repair muscles after exertion. Women have less testosterone, so they have more muscle fatigue. The study also showed that men are better protected from a biological link between fatigue and pain.
Other studies have shown gender-based differences in the stress-hormone cortisol which researchers say is low in FMS and ME/CFS. That makes the body more susceptible to damage from stress, either physical or emotional. (Physical stress includes illness, over-exertion, even waking up in the morning.)
In a UCLA study not related to FMS and ME/CFS, researchers discovered that women in unhappy marriages have poor cortisol release compared to happily married women. Men's cortisol levels, however, were not linked to marital satisfaction. This could help explain why conditions characterized by low cortisol are more common in women.
Gender & Brain Chemistry
A 2008 Swedish study suggested the brain's serotonin system functions differently in men and women. (Serotonin is a neurotransmitter that deals with pain, sleep, anxiety and depression, and experts say it's low in FMS and ME/CFS.)
The researchers demonstrated that women naturally have more serotonin receptors and lower levels of a protein that transports serotonin back into the nerve cells that secrete it (a process called re-uptake).
Many of the drugs commonly prescribed for FMS and ME/CFS slow down re-uptake (SSRIs and SNRIs), and the researchers say this can help us understand why men and women respond differently to these drugs. They also say the drugs should be tested on men and women separately, and also on women both before and after menopause.
The study showed serotonin-system differences between women who do and don't get PMS symptoms, regardless of the time of the month, suggesting that the PMS-prone brains don't respond as well to hormonal swings. PMS is a common overlapping condition with FMS and ME/CFS and often aggravates symptoms.
A separate study shows low serotonin levels affect men and women differently as well. Researchers say it makes men more impulsive but doesn't cause other mood changes, while women reported worsening moods and became more cautious.
The Immune System, Fibromyalgia and Chronic Fatigue Syndrome
More women get conditions that are believed, at least in part, to involve an over-active immune system. They include FMS, ME/CFS, celiac disease, IBS and others.
Many cases of ME/CFS are believed to be caused by viral infection which somehow leaves the immune system in an overactive state, similar to what everyone experiences when their body is fighting a virus. The difference with ME/CFS, however, is that the body never stops fighting. Researchers say some cases of ME/CFS may be linked to a chronic infection, while others could be caused by a virus that leaves behind permanent changes in the immune system.
"Once the immune system becomes highly activated, it can produce inflammatory chemicals that fuel many types of muscle and joint pain," Peckman says. Then, the inflammation can affect nerves where they're most vulnerable.
Genetics, Gender & Fibromyalgia
Experts have long believed that genetic predisposition plays a role in whether you'll develop FMS or ME/CFS when you're exposed to the right (or perhaps wrong) set of factors, such as sleep disorders, viral infections or extreme stress.
Laurence Bradley, PhD of the University of Alabama at Birmingham is looking into whether this genetic tendency in FMS is also gender-based. He says some evidence shows the disorder occurs more frequently among sisters than it does among brothers. The genetics study is taking healthy brothers and sisters of women with fibromyalgia and comparing their pain sensitivities with those of a control group.
Bradley's team will be looking at serotonin levels, hoping to confirm the theory that people with FMS have a genetic abnormality that regulates serotonin production.
If Bradley's study confirms this genetic abnormality, he says it will improve our understanding of FMS and could also help identify who is most at risk.
Traditional Gender Roles
Some experts think that many men are stoic about their symptoms because they believe talking about them makes them appear weak. Because they don't tell their doctors what's going on, they can't be diagnosed.
Also, because FMS and ME/CFS are often thought of as "female complaints," doctors may be less likely to think about them as possible diagnoses for male patients.
Sources: 2008 The American Physiological Society. All rights reserved. "Enhanced muscle fatigue occurs in male but not female ASIC3-/-mice" 2008 Elsevier B.V. All rights reserved. "Women more Depressed and Men more Impulsive with Reduced Serotonin Functioning" 2008 News-Medical.Net. All rights reservied. "Brain's serotonin system differs between men and women" 2007 UAB Health System. All rights reserved. "Chronic Pain Studies Examine Fibromyalgia" 2008 University of California Regents. All rights reserved. "For women, marital distress means less relief from stress"
2008 The American Physiological Society. All rights reserved. "Enhanced muscle fatigue occurs in male but not female ASIC3-/-mice"
2008 Elsevier B.V. All rights reserved. "Women more Depressed and Men more Impulsive with Reduced Serotonin Functioning"
2008 News-Medical.Net. All rights reservied. "Brain's serotonin system differs between men and women"
2007 UAB Health System. All rights reserved. "Chronic Pain Studies Examine Fibromyalgia"
2008 University of California Regents. All rights reserved. "For women, marital distress means less relief from stress"