According to the National Fibromyalgia Association [here], FMS afflicts an estimated 10 million people in the United States and an estimated 3% to 6% of the world population. Up to 90% of persons with the disorder are women, but it also occurs in men and children of all age and ethnic groups. FMS is characterized by widespread pain and a range of functional disturbances.
Last May 2010, a research team from Norway reported on a large, retrospective, longitudinal study of women, which concluded that being overweight or obese significantly increased the risk of developing fibromyalgia. Body mass index, or BMI, was viewed as an independent risk factor for fibromyalgia (p<0.001), and overweight or obese women were reported to have a 60% to 70% higher risk compared with women of normal weight [Mork et al. 2010; see discussion in UPDATES posting here].
Now, a recent study in the Journal of Pain reports a similar association between obesity and fibromyalgia largely in women [Okifuji et al. 2010]. Researchers at the University of Utah enrolled 215 persons diagnosed with FMS, who had been recruited to be part of a larger clinical study. Each participant completed self-report inventories to assess symptoms and they also underwent physical performance testing, tender point examination, and a sleep assessment. Subjects were mostly female (95%) and white (95%), 45 years of age on average, with mean FMS duration of roughly 13 years, and a mean BMI of 30.53 (47% were in the obese range, BMI >30, and an additional 30% were overweight, BMI = 25-30. [Normal range is 18.5-24.9; BMI is calculated as weight in kg ÷ height in meters squared or weight in lbs. x 703 ÷ height in inches squared.])
Consistent with previous findings, obese women in this study showed increased pain sensitivity, which was more pronounced in lower body areas. They also had impaired flexibility in the lower body, reduced strength, shortened sleep time and greater restlessness when they did sleep. Therefore, Okifuji and colleagues concluded that obesity is a common comorbidity of fibromyalgia that may compromise clinical outcomes. They also proposed that weight loss may improve fibromyalgia symptoms and overall quality of life, perhaps resulting from patients adopting healthier lifestyles and taking more positive attitudes toward symptom management.
COMMENTARY: As might be expected, the mass media widely reported on this study under headlines similar to “Obesity Plagues Women with Fibromyalgia.” Many news reports further stated, “the good news is that losing weight brings relief.” Therefore, a myth may have arisen that FMS is a disease of middle-aged overweight women, and if they simply lose weight they will overcome the disorder. Like all myths there are bits of fact distorted by “mythunderstandings.” Here are some observations from the available evidence…
- Neither Okifuji et al.  nor Mork and colleagues  tried to determine which condition, obesity or FMS, had developed first. Therefore, they could not begin to determine cause and effect, even though media reports implied that obesity is directly related to FMS.
- It may be that FMS is more a risk factor for excess weight than the reverse. One writer, Adrienne Dellwo, seems to pose the correct question — “Fibromyalgia & Obesity: Cause, Effect, or Vicious Cycle?” [available here] — and provides a practical explanation…
“It's not surprising that, as a group, we're overweight: most of us are far less active than we used to be; some of us take medications that cause weight gain; a lot of doctors and researchers believe we have some sort of metabolic problem; we're prone to sleep disorders, and a sleep-deprived body won't lose weight. So yes, we get fat.”
- In regard to medications, Okifuji and colleagues  noted that most FMS patients were taking analgesics, antidepressants, antiepileptics, muscle relaxants, and/or sedatives of various types. Some of these can contribute to weight gain; however, differences between groups were not reported, other than that obese patients were using nonbenzodiazepine sedatives to a much lesser extent than overweight or normal weight subjects.
- Another question needs asking: Was the prevalence of excess body weight in study participants — average BMI 30.1; 47% in obese range, 30% overweight — exceptionally large and atypical? In a recently reported large study of patients (n=1,160, 57% women) being treated for various chronic noncancer pain conditions — neuropathic, nociceptive, and a mix of the two, but not FMS — the mean BMI was 30.1 [Passik et al. 2010]; identical to the mean in this FMS study. According to the Centers for Disease Control, 34% of adult Americans are overweight but not obese, another 34% are in the obese range, and an additional 6% are extremely obese [obesity data here], or a total 74% having weight problems compared with a 77% total in the FMS study (a difference that is probably not statistically significant).
Two possibilities are suggested by these data: 1) excess weight is common in many chronic pain conditions, including FMS, and is more of a consequence than a precursor, and/or 2) persons with chronic pain are actually no more overweight or obese than the population at large. In either case, excess weight among FMS patients is not unexpected and may not be in any way a diagnostic feature of the disorder.
- Relying on the body mass index for group allocation in research of this sort may have little external validity to begin with. Okifuji et al.  concede that, while BMI is a convenient proxy measure of body composition, and is correlated with overall body fat, it fails to take into account individual factors, such as location of body fat, muscle mass, tallness, bone structure, age, and ethnic factors.
- Finally, if body weight or BMI are a primary influence on developing FMS then weight loss should greatly improve FMS symptoms (as media reports promised). Surprisingly, this has not been thoroughly studied. In one of the few reported investigations to date — a pilot study by Shapiro et al.  at the State University of New York, Albany — 31 overweight (BMI≥25), middle-aged (mean 54 years) women with FMS completed a 20-week weight-loss program. At baseline, BMI was associated with more functional disability but not correlated with pain itself. Participants lost an average of 9 lbs and there were improvements in pain, pain interference, body satisfaction, and quality of life. As a complication, the study did not control for medication used by patients, which might have affected changes in symptoms, particularly pain. While the authors concluded that weight loss is beneficial for overweight women with FMS, which seems reasonable for any overweight person with chronic pain, they could not confirm that BMI is related to developing FMS. And, it is still unclear whether exercise, better nutrition, or weight loss itself is the best predictor of improved FMS symptoms and quality of life.
ADDENDUM contributed by Rae Marie Gleason, Executive Director, National Fibromyalgia Association (NFA): This article above is a great example of non-biased publishing. Sadly, in the world of fibromyalgia strong bias's often impinge on scientific thoughts and actions. The wildly erratic swings between FM pros's and con's in the scientific and medical communities often taint professional approaches to better patient treatment and care. All of the points made by Dr. Leavitt regarding obesity in general in today's American society, plus the mention of problems with FM medications (off and on label) causing weight gain, combined with a sedentary life-style experienced by many FM patients because of their painful condition, all bode well as possible explanations regarding the obesity/FM link reported in the Utah and other studies. Rational thinking is needed by scientists pursuing answers to the many perplexities of fibromyalgia. Weighing and measuring scientific evidence in an unbiased manner and remembering to consider extenuating circumstances in this patient population that are common in the general population, is imperative in understanding the complexities of this illness and the scientific theory being tested.
> Mork PJ, Vasseljen O, Nilsen TIL. Association between physical exercise, body mass index, and risk of fibromyalgia: Longitudinal data from the Norwegian Nord-Trøndelag Health Study. Arthritis Care & Research. 2010;62(5):611-617 [abstract here].
> Okifuji A, Donaldson GW, Barck L, Fine PG. Relationship Between Fibromyalgia and Obesity in Pain, Function, Mood, and Sleep. J Pain. 2010(Dec);11(12):1329-1337 [abstract].
> Passik SD, Messina J, Golsorkhi A, Xie F. Aberrant Drug-Related Behavior Observed During Clinical Studies Involving Patients Taking Chronic Opioid Therapy for Persistent Pain and Fentanyl Buccal Tablet for Breakthrough Pain. J Pain Symptom Manag. 2011(Jan);41(1):116-125 [abstract here].
> Shapiro JR, Anderson DA, Danoff-Burg S. A pilot study of the effects of behavioral weight loss treatment on fibromyalgia symptoms. J Psychosomatic Res. 2005;59(5):275-282 [article PDF here].