Fibromyalgia and Obesity

The Association Between Body Mass Index and Disability, Depression, History of Abuse, Medications, and Comorbidities

Carmen E. Gota, MD; Sahar Kaouk; William S. Wilke, MD

Disclosures

J Clin Rheumatol. 2015;21(6):289-295. 

In This Article

Discussion

Almost 3 quarters of FM patients are overweight (29.9%) or obese (43.8%). These numbers reflect the high prevalence of obesity in FM patients in the United States. Furthermore, our rate is in excess of the 35% US rate and the 21.4% to 33% European rates reported in FM as well as the 35.1% rate reported for the US general population.[7,12,13] Our higher prevalence of obesity also suggests that the rate of obesity is rising in the United States when compared with the 32.8% prevalence reported by Yunus et al in 2002.[32]

Both FM and obesity are associated with deregulation of the hypothalamic pituitary axis and to higher levels of cortisol and epinephrine compared with controls.[33] Adipokines may have a role in mediating the FM obesity link. Serum levels of leptin, a hormone with a role in energy expenditure, fat regulation, and suppression of hunger, were measured in FM patients.[34–36] Only 1 study demonstrated lower leptin levels versus controls, which correlated with symptom severity.[34]

Obesity in FM is associated with the same variables as in the general population, including lack of exercise, history of physical and sexual abuse, depression, medical comorbidities, hypothyroidism, the number of musculoskeletal surgeries, and the number of medications taken for FM.

Studies of obesity in the general population show that it is associated with medical comorbidities,[37] psychiatric pharmacotherapy,[38] depression, poor physical function,[34] and sexual and physical abuse.[39] To our knowledge, the relationship we observed between BMI and the number of medical comorbidities has not been previously reported in an FM cohort, although it has been demonstrated in the general population. Longitudinal prospective studies show that obesity predicts an increased incidence of medical comorbidities including type 2 diabetes, cancer and cardiovascular disease, asthma, gallbladder disease, osteoarthritis, and chronic back pain.[37]

The bivariate correlation of the HAQ-DI with increasing BMI is of interest and may help to validate a relationship of BMI to medical comorbidities. In rheumatoid arthritis, HAQ-DI progression is associated with the number of medical comorbidities.[38] These 2 interrelationships among painful conditions may provide another nonspecific link of BMI to medical comorbidities.

Patients with FM and obesity are likely to accumulate other obesity-related comorbidities, such as depression, similar to the general population, suggesting that the association is independent of FM. Overweight and obese women in the general population are at increased risk of incident major depressive disorder.[10] This association between obesity and mental illness is complex and bidirectional, mediated through physical health factors secondary to obesity, coupled with societal attitudes toward those who are obese, and iatrogenic treatment factors linked to psychiatric pharmacotherapy.[39] Others reported the effect of depression on BMI to be partially mediated by weight and shape concerns, poor sleep quality, and binge eating disorder.[17]

Several studies of obesity in FM patients, have also found significant associations between depression and BMI.[11,31,43] We confirm these results in our cohort; obese FM patients reported significantly higher PHQ-9 depression scores compared with normal-weight FM patients (13.2 [6.6] vs 10.5 [6], respectively). Like our study, they did not show an increased prevalence of anxiety. Unlike our study, they did not find associations of BMI with bipolar disorder factors.

Compared with normal-weight patients, obese FM patients in our study were taking more medications for FM, including SSRIs, other antidepressants, and antipsychotic drugs, as well as gabapentinoids, all known to potentially cause weight gain.[41,42] In a multivariate model to predict BMI change, the number of medications for FM, but not depression measured by PHQ-9, was an independent predictor of increased BMI, raising the hypothesis that the effect of depression on obesity in FM patients may be mediated by the quantity of FM drugs.

Compared with normal-weight FM patients, 48% versus 33.9% of obese FM patients reported a history of abuse (physical and sexual), and 17.3% versus 6.8%, a history of sexual abuse in our study. The association between abuse and obesity, as well as the association between abuse and functional somatic syndromes/FM, is well reported.[40,44] A review of 18 studies with 13,095 subjects confirmed the association of FM diagnosis with both self-reported physical and sexual abuse in childhood and adulthood.[45]

To our knowledge, only 1 other group analyzed the relationships of abuse (verbal, physical, sexual, and emotional) to increasing BMI and FM severity in 2 publications.[11,31] No significant differences of abuse among BMI categories were found. Increasing BMI did correlate with FM symptoms.[31] Of interest, compared with our study, lower prevalence of abuse and sexual abuse was reported.

In our multivariate model, we found that sexual abuse was 1 of 2 factors significantly correlated with increasing BMI. Others have found that increasing BMI is associated with sexual abuse in the general population.[46] The relationship of sexual abuse to BMI appears to be unrelated to FMS and operates nonspecifically.

It has been hypothesized that the high incidence of obesity in FM patients is related to the lack of physical activity.[33] A previous study showed that the modest impact of increasing BMI on physical impairment in FM was related to pain interference and inactivity.[8] Less than 10% of obese FM patients in our study reported performing regular aerobic exercise, compared with 25% of normal-weight FM patients, reflected in the significant but small negative correlation (r = -0.183) between BMI and exercise, consistent with previous reports.[32]

Obesity in FM does not correlate with FM symptoms and measures but is associated with general measures of disability (HAQ-DI).

We found no associations between BMI and FM symptoms and measures, including FIQ total and its 10 subset scores, or with meeting the ACR 1990 criteria and survey criteria, contrary to other studies.[8–13,43,47] This was surprising because we found a significant correlation between BMI and disability measured by HAQ-DI (r = 0.254; P < 0.0001) in agreement with previous reports,[32] and with data from the general population.[48,49] We did, however, find a strong correlation between HAQ-DI and FIQ physical impairment (r = 0.598, P < 0.001).

Different from our data, an analysis of 888 FM patients selected to participate in a brief interdisciplinary program found significant differences between BMI groups with regard to total FIQ score, FIQ physical function, FIQ interference with job/house work, FIQ pain, FIQ fatigue, FIQ stiffness, FIQ depression, and FIQ anxiety.[9] Of note, even in studies where such correlations between BMI and FIQ total and subsets were observed, the magnitude was small.[31] In agreement with our findings, a study designed similarly to ours found no correlation between BMI and VAS pain, VAS fatigue, feeling swollen, sleep difficulties, irritable bowel syndrome, numbness feeling, and "hurt all over."[32] The interpretation of the sleep apnea data in our study is difficult because of the small number of patients.

It is possible that in a tertiary care center such as ours, a small impact of BMI on FM process may be difficult to detect, because our population is strongly skewed toward moderate and severe FM in all weight groups. In addition, many of the symptoms included are disease defining rather than severity defining, for example, widespread pain reported by 96.7%, fatigue by 98.3%, and unrefreshing sleep by 84.9%, and we did not perform more discriminant measures of distress such as tender point total counts and tender point tenderness severity. Our normal-weight FM patients had mean FIQ score of 66.7 (SD, 19.6), considered in the severe range for impairment[50] and higher than FIQ scores reported in obese FM patients in other studies, 62.1 (SD, 17.8) to 66.5 (SD, 16.4).[11,43] Our findings also suggest that HAQ-DI may be a more discriminative measure of disability in patients with severe FM and obesity, as it quantifies basic functions such as eating, grooming, reaching, dressing, and rising from a chair, rather than more complex activities such as washing clothes, doing laundry, and preparing meals in the FIQ disability index.[30,51] In addition, while BMI is associated with both upper- and lower-extremity disability, the association is strongest for the lower extremities, better reflecting items in the HAQ-DI.[52]

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