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 in several directions:
- Hormones
- Brain chemistry
- Immune systems & inflammation
- Genetics
Hormones, Fibromyalgia and ME/CFS
When looking a 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 published in 2008 suggests that testosterone, the male hormone, plays a role in preventing muscle fatigue - a symptom of both FMS and ME/CFS, and many other chronic pain conditions.
The researchers found that a certain protein works with testosterone to repair muscles after exertion. Because women have less testosterone, they're far more likely to have muscle fatigue.
In addition, this study demonstrated a biological link between fatigue and pain and that men are better protected from it.
Studies have also shown gender-based differences in the stress-hormone cortisol which, according to researchers, is low in people with FMS and ME/CFS. This puts your body at a disadvantage when dealing with stress, either physical or emotional. (Physical stress includes illness, over-exertion or 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 both happily married women and all men in the study, regardless of marital satisfaction. If women's cortisol levels are more easily thrown off than men's, that could help explain why conditions characterized by low cortisol are more common in women.
Brain Chemistry in Fibromyalgia & Chronic Fatigue Syndrome
A Swedish study released in 2008 suggest the brain's serotonin system functions very differently in men than in women. (Serotonin is a neurotransmitter that deals with pain, sleep, anxiety and depression, and experts say is low in people with FMS. Studies are split as to whether it's low or high in those with ME/CFS.)
In this new study, researchers demonstrated that women naturally have more serotonin receptors and lower levels of the 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 are selective serotonin re-uptake inhibitors (SSRIs) or serotonin and norepinephrine re-uptake inhibitors (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 women's brains don't respond as well to hormone swings. This could help explain why 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 comes, causes permanent changes in the immune system, then goes away.
"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 fibromyalgia 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.
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"
