To examine the association between body mass index (BMI) and symptom severity and quality of life (QOL) in patients with fibromyalgia.
To examine the association between body mass index (BMI) and symptom severity and quality of life (QOL) in patients with fibromyalgia.
We assessed BMI status and its association with symptom severity and QOL in 888 patients with fibromyalgia who were seen in a fibromyalgia treatment program and who completed the Fibromyalgia Impact Questionnaire (FIQ) and the Short Form 36 (SF-36) health survey.
The BMI distribution of nonobese (BMI <25.0 kg/m2), overweight (BMI 25.0–29.9 kg/m2), moderately obese (BMI 30.0–34.9 kg/m2), and severely obese (BMI ≥35.0 kg/m2) patients was 28.4% (n = 252), 26.8% (n = 238), 22.2% (n = 197), and 22.6% (n = 201), respectively. Age was significantly different among the 4 groups, with those having a greater BMI being older (P = 0.004). After adjustment for age, group differences were significant in the number of tender points (P = 0.003) and the FIQ and SF-36 scores. The groups with the greater BMI had greater fibromyalgia-related symptoms with worse FIQ total scores (P < 0.001), as well as worse scores in the FIQ subscales of physical function (P < 0.001), work missed (P = 0.04), job ability (P = 0.003), pain (P < 0.001), stiffness (P < 0.001), and depression (P = 0.03). These groups also had poorer SF-36 scores in physical functioning (P < 0.001), pain index (P = 0.005), general health perceptions (P = 0.003), role emotional (P = 0.04), and physical component summary (P < 0.001). Post hoc analysis among the 4 groups showed that differences resided primarily in the severely obese group compared with the other groups.
In patients with fibromyalgia, severe obesity (BMI ≥35.0 kg/m2) is associated with higher levels of fibromyalgia symptoms and lower levels of QOL.
Fibromyalgia, which affects 3–5% of the US population, is a chronic pain condition characterized by widespread pain, tenderness, and various associated symptoms, including fatigue, morning stiffness, unrefreshing sleep, and cognitive symptoms (1–3).
The number of people who are overweight and obese is increasing in the US and approximately one-third of the population would be classified as obese (4). A number of studies have demonstrated an association between obesity and quality of life (QOL) in the general population. Those who had a higher body mass index (BMI) showed lower QOL scores in both the physical and emotional components, and these impairments were more pronounced in the physical dimensions than the others (5–8). Obesity was also associated with more physical pain (6). The QOL impact of obesity class showed that severe and extreme obesity was associated with greater physical impairment than moderate obesity (5).
Obesity is comorbid with a number of chronic pain syndromes, including back and neck pain, migraine, osteoarthritis, and increased general pain (9–12). Studies on the co-occurrence of chronic pain conditions and overweight/obesity indicate that overweight/obese individuals are at a greater risk for chronic pain, as well as for increased severity, which is thought to be related to mechanical-structural factors due to increased pressure on the joints from the additional weight, metabolic abnormalities, and behavioral changes (11, 13–17).
Higher rates of people being overweight or obese, ranging from 47–73%, have been reported in patients with fibromyalgia (18–20). A recent longitudinal study demonstrated that BMI was an independent risk factor for fibromyalgia, and overweight or obese women had a 60–70% higher risk compared with women of normal weight (21). Associations between obesity, increased pain sensitivity, and poorer physical function and sleep have been reported in patients with fibromyalgia (18–20). However, these reports did not find a significant relationship between pain and BMI (19, 20). While the Fibromyalgia Impact Questionnaire (FIQ) has been the common outcome measure used with this population, the literature did not identify specific differences in the self-reported scores between normal weight, overweight, and obese groups in populations with fibromyalgia (18, 19). In terms of QOL, a greater BMI was correlated with lower levels of QOL in patients with fibromyalgia, but significant differences in QOL were not demonstrated between normal, overweight, and obese groups (18).
World Health Organization (WHO) BMI classification divides obesity into class I (BMI 30.0–34.9 kg/m2, moderately obese), class II (BMI 35.0–39.9 kg/m2, severely obese), and class III (BMI ≥40.0 kg/m2, extremely obese) because management options differ for those with a BMI >35 kg/m2 due to the concurrent severe risk of comorbidities (22, 23). The prevalence of severe or extreme obesity is increasing at a faster rate among US adults than moderate obesity (4, 24). Although obesity is common in patients with fibromyalgia, how the degree of obesity, especially severe obesity, impacts fibromyalgia-related symptoms and QOL has not been reported to date. The purpose of the present study was to examine the association between BMI, symptom severity, and QOL in patients with fibromyalgia.
Obesity is common in patients with fibromyalgia; approximately one-half of our patients were obese and one-quarter were severely obese.
Obese patients had higher levels of fibromyalgia symptoms and lower levels of quality of life than nonobese or overweight patients.
The differences in self-reported symptoms were primarily from the severely obese group (body mass index ≥35 kg/m2).
Our large sample size allowed us to classify and examine differences in grade of obesity of moderate and severe obesity separately.
The study population was from our research group's previously reported study of 6- to 12-month treatment outcome after a brief interdisciplinary Fibromyalgia Treatment Program (FTP) (25). The present study was approved by the institutional review board, and all participants provided written consent to participate in the study.
Our participants were seen in the FTP and had the confirmed diagnosis of fibromyalgia, according to the 1990 American College of Rheumatology criteria for the classification of fibromyalgia (2), during the study period from May 1, 2001 to April 30, 2004 (15). Among the 988 patients seen during the study period, 100 patients had incomplete data on BMI and were excluded from further analysis. The final study population consisted of 888 patients who were age >18 years, had BMI information based on objectively measured weight and height, and had completed the FIQ and the Short Form 36 (SF-36) health survey at the time of evaluation in the FTP. All participants underwent a standardized evaluation, including a tender-point assessment with a registered nurse. Demographic and social variables and the number of tender points were abstracted from the medical record.
BMI is defined as the weight in kilograms divided by the square of the height in meters (kg/m2). The WHO classification criteria were used to identify patients who were underweight (BMI <18.5 kg/m2), normal weight (BMI 18.5–24.9 kg/m2), overweight (BMI 25.0–29.9 kg/m2), and obese (BMI ≥30.0 kg/m2) (22). By the WHO classification criteria, the obese group was divided further into class I (BMI 30.0–34.9 kg/m2), class II (BMI 35.0–39.9 kg/m2), and class III (BMI ≥40.0 kg/m2).
The number of study patients in the underweight group was small with only 15 patients (1.7%). The class III group was small compared with the other BMI groups, with 83 patients (9.3%) (Table 1). Therefore, we merged the underweight into the normal group and formed a nonobese group. We combined the class II and class III groups into one severely obese group for the purpose of analysis. Our final BMI classification consisted of 4 groups: nonobese (BMI <25.0 kg/m2), overweight (BMI 25.0–29.9 kg/m2), moderately obese (BMI 30.0–34.9 kg/m2), and severely obese (BMI ≥35.0 kg/m2).
|WHO classification||BMI (kg/m2)||Patients, no. (%) (n = 888)|
Participants completed the FIQ and the SF-36 at the time of their evaluation in the FTP. The FIQ was developed in 1991 and has been validated as an effective tool for assessing health status of patients with fibromyalgia (26). It is a self-administered questionnaire that measures multiple domains of fibromyalgia symptoms and functional impairment and contains 20 questions that assess the following 10 items: physical functioning, overall well-being in the previous week, days of work missed, and symptoms of pain, fatigue, morning tiredness, stiffness, job difficulty, anxiety, and depression. The latter 7 questions were measured using a 100-mm visual analog scale. Scores range from 0–100, with a high score indicating a greater impact of fibromyalgia (26). The FIQ was scored according to the directions outlined by Bennett (27).
The SF-36, which assesses health-related QOL, was developed as a potential tool for monitoring patient outcomes in a busy clinical setting (28, 29). It is a self-administered questionnaire that measures 8 health concepts: general health rating, physical functioning, role physical, pain index, general health score, vitality score, social functioning, and role emotional, as well as physical composite and mental composite scores. The SF-36 score ranges from 0–100, and higher scores indicate better health status (29).
Demographic and social characteristics, FIQ and SF-36 scores, and the number of tender points were compared across the BMI groups through one-way analysis of variance for continuous variables and chi-square tests for categorical variables. Because age differed significantly across the BMI groups, we also performed age-adjusted analyses using multiple linear regression. In cases where the omnibus P value testing across the 4 groups was statistically significant (at an alpha level of 0.05), post hoc pairwise tests were performed, again using linear regression models to adjust for age. A Bonferroni correction for multiple comparisons was applied for these post hoc pairwise tests. All pairwise comparisons between the 4 groups equaled 6 comparisons, for a Bonferroni P value of 0.05, 0.06, or 0.008. Analyses were performed using JMP software, version 8 (SAS Institute).
The BMI distribution of the nonobese, overweight, moderately obese, and severely obese patient groups was relatively even with 28.4% (n = 252), 26.8% (n = 238), 22.2% (n = 197), and 22.6% (n = 201), respectively (Table 1). Of the patients, 72% were overweight or obese. The mean ± SD BMI of our patients was 29.8 ± 7.2 kg/m2. The patient characteristics in each BMI category are presented in Table 2. The mean ± SD age was 49 ± 13 years. Group differences in age were significant (P = 0.004), with the higher BMI associated with increased age. The number of tender points differed significantly between the groups (P = 0.04), with higher BMI associated with an increased number of tender points. There were no other significant group differences in the patient characteristics.
|Characteristics||Nonobese (n = 252)†||Overweight (n = 238)‡||Moderately obese (n = 197)§||Severely obese (n = 201)¶||P|
|Female||241 (95.6)||218 (91.6)||187 (94.9)||194 (96.5)|
|Male||11 (4.4)||20 (8.4)||10 (5.1)||7 (3.5)|
|Age, mean ± SD years||47 ± 13.7||49 ± 12.5||51 ± 12.5||50 ± 11.6||0.004|
|Yes||74/248 (29.8)||64/233 (27.5)||54/193 (28.0)||68/199 (34.2)|
|No||174/248 (70.2)||169/233 (72.5)||139/193 (72.0)||131/199 (65.8)|
|Yes||36/250 (14.4)||36 (15.1)||26/196 (13.2)||23 (11.4)|
|No||214/250 (85.6)||202 (84.9)||170/196 (86.7)||178 (88.6)|
|Married||192 (76.2)||181 (76.1)||154 (78.2)||146 (72.6)|
|Nonmarried||55 (21.8)||56 (23.5)||39 (19.8)||47 (23.4)|
|Widowed||5 (2.0)||1 (0.4)||4 (2.0)||8 (4.0)|
|Employed||136 (54.0)||133 (55.9)||105 (53.3)||109 (54.2)|
|Homemaker||22 (8.7)||26 (10.9)||15 (7.6)||12 (6.0)|
|Retired||29 (11.5)||32 (13.5)||28 (14.2)||23 (11.4)|
|Unemployed||65 (25.8)||47 (20.0)||49 (24.9)||57 (28.4)|
|<12 grades||9/249 (3.6)||6/233 (2.6)||6/195 (3.1)||5/198 (2.5)|
|High school||67/249 (26.9)||74/233 (31.8)||64/195 (32.8)||69/198 (34.9)|
|Some college/technical||75/249 (30.1)||74/233 (31.8)||63/195 (32.3)||71/198 (35.9)|
|College/graduate school||98/249 (39.4)||79/233 (33.9)||62/195 (31.8)||53/198 (26.8)|
|No. of tender points, mean ± SD||15.9 ± 2.3||16.1 ± 2.1||16.1 ± 2.1||16.6 ± 2.0||0.004/0.003#|
The FIQ score comparison by BMI category is reported in Table 3.After adjustment for age, there were significant group differences. Greater fibromyalgia-related symptoms and functional impairment was found in the higher BMI groups for total FIQ score (P < 0.001) and for the FIQ subscales of physical function (P < 0.001), work missed (P = 0.04), job ability (P = 0.003), pain (P < 0.001), stiffness (P < 0.001), and depression (P = 0.03). There were no significant group differences in the FIQ subscale scores of feel good, fatigue, morning tiredness, and anxiety. The SF-36 comparison by BMI category is shown in Table 4. After adjustment for age, group differences were significant, with the lower SF-36 scores in the higher BMI groups indicating poorer QOL in the subscales of physical functioning (P < 0.001), pain index (P = 0.005), general health perceptions (P = 0.003), role emotional (P = 0.04), and physical component summary (P < 0.001). There were no significant group differences in the SF-36 scores in role physical, vitality, social functioning, mental health index, and mental component summary.
|FIQ characteristics||Nonobese (n = 252)†||Overweight (n = 238)‡||Moderately obese (n = 197)§||Severely obese (n = 201)¶||Age-adjusted P|
|Total score||60.7 ± 16.9||61.89 ± 17.1||62.3 ± 17.1||66.5 ± 16.4||< 0.001|
|Physical function||4.3 ± 2.3||4.4 ± 2.3||4.7 ± 2.2||5.2 ± 2.2||< 0.001|
|Feel good||7.6 ± 2.5||7.7 ± 2.2||7.7 ± 2.2||7.8 ± 2.3||0.64|
|Work missed||3.8 ± 3.6||4.0 ± 3.6||3.8 ± 3.7||4.6 ± 3.7||0.04|
|Job ability||6.5 ± 2.4||6.7 ± 2.5||6.8 ± 2.4||7.2 ± 2.3||0.003|
|Pain||6.8 ± 2.1||7.0 ± 2.1||7.2 ± 2.0||7.5 ± 2.0||< 0.001|
|Fatigue||8.0 ± 2.1||8.1 ± 2.1||8.1 ± 2.0||8.4 ± 1.9||0.09|
|Morning tiredness||7.8 ± 2.2||7.8 ± 2.3||7.8 ± 2.4||8.0 ± 2.2||0.39|
|Stiffness||6.9 ± 2.4||7.2 ± 2.3||7.4 ± 2.3||7.7 ± 2.1||< 0.001|
|Depression||3.8 ± 3.1||4.1 ± 3.2||4.0 ± 3.3||4.6 ± 3.2||0.03|
|Anxiety||5.1 ± 2.9||4.8 ± 3.1||4.6 ± 3.1||5.2 ± 3.0||0.09|
|SF-36 characteristics||Nonobese (n = 252)†||Overweight (n = 238)‡||Moderately obese (n = 197)§||Severely obese (n = 201)¶||Age-adjusted P|
|Physical functioning||46.3 ± 23.3||44.1 ± 22.8||37.4 ± 20.7||29.0 ± 18.1||< 0.001|
|Role physical||9.5 ± 21.3||8.8 ± 20.7||7.4 ± 19.0||6.4 ± 15.3||0.36|
|Pain index||27.1 ± 16.0||26.6 ± 14.8||24.6 ± 13.2||22.9 ± 14.6||0.005|
|General health perceptions||39.6 ± 21.2||38.1 ± 20.1||41.0 ± 21.3||34.3 ± 19.6||0.003|
|Vitality||18.2 ± 17.8||19.1 ± 16.7||17.9 ± 16.1||15.9 ± 14.8||0.13|
|Social functioning||42.0 ± 25.5||40.3 ± 25.5||40.1 ± 25.7||37.2 ± 24.1||0.053|
|Role emotional||51.1 ± 43.2||49.4 ± 43.3||43.0 ± 41.1||41.2 ± 41.6||0.04|
|Mental health index||57.6 ± 21.2||57.5 ± 20.3||57.6 ± 21.4||54.7 ± 21.5||0.31|
|Physical component summary||28.3 ± 8.1||27.7 ± 7.8||26.8 ± 7.0||24.5 ± 6.7||< 0.001|
|Mental component summary||40.3 ± 11.9||40.1 ± 11.8||40.0 ± 11.7||39.4 ± 11.7||0.61|
Age-adjusted post hoc analyses between the severely obese and nonobese groups showed significant differences in all variables (P < 0.008) except for role emotional (P = 0.01) (Table 5). The severely obese group also had significantly poorer scores than the overweight and moderately obese groups for SF-36 physical functioning and physical component summary scores. Additionally, the severely obese group had significant differences from the overweight group for the FIQ total, physical function subscale, pain subscale, and the SF-36 pain index scores and, from the moderately obese group, the SF-36 general health perceptions.
|Characteristics||Severely obese vs. nonobese†||Severely obese vs. overweight‡||Severely obese vs. moderately obese§||Moderately obese vs. nonobese||Moderately obese vs. overweight||Overweight vs. nonobese|
|Total score||< 0.001¶||0.003¶||0.02||0.11||0.60||0.26|
|Physical function||< 0.001¶||< 0.001¶||0.05||0.03||0.09||0.63|
|Job ability||< 0.001¶||0.03||0.13||0.04||0.51||0.13|
|Physical functioning||< 0.001¶||< 0.001¶||< 0.001¶||< 0.001¶||0.001¶||0.36|
|General health perceptions||< 0.001¶||0.05||0.002¶||0.87||0.22||0.14|
|Physical component summary||< 0.001¶||< 0.001¶||0.002¶||0.03||0.22||0.35|
|Tender points||< 0.001¶||0.01||0.02||0.20||0.92||0.21|
Age-adjusted post hoc analysis between the moderately obese group and 1) the nonobese group and 2) the overweight group showed no significant differences in the variables, except for the FIQ stiffness subscale from the nonobese group and the SF-36 physical functioning from both the overweight and nonobese groups. No differences were found between the overweight group and the nonobese group.
Our study shows that obesity is common in patients with fibromyalgia; approximately half of our patients were obese and one-quarter were severely obese. Obesity was found to increase with age and was associated with increased fibromyalgia symptom severity, lower levels of QOL, deterioration of physical ability, and higher number of tender points. The symptom severity is more pronounced when the obesity is more severe. The group differences were found primarily in comparisons of the severely obese patients with the nonobese patients and with the overweight patients, as well as the moderately obese patients. The severely obese patients had significantly higher FIQ pain scores and SF-36 pain index than the nonobese and overweight patients. When comparing the moderately obese patients with the overweight patients and with the nonobese patients, the significant differences were limited to physical functioning and stiffness; no differences were found between the overweight and the nonobese patients.
The 45% rate of obesity among our patients with fibromyalgia is higher than the obesity rate of one-third of the US population, based on objectively measured weight for the US as a whole (4). Furthermore, one-half of our obese patients were severely obese (BMI ≥35 kg/m2). Our obesity rate was similar to other recent studies (45–50%) in fibromyalgia, which were done without the subdivision of obese classes (18, 19, 30). However, our obesity rate was higher than the 32% rate reported by Yunus et al (20). Their study classified obesity into 3 classes (I, II, and III), and their classes II and III (i.e., severely obese) comprised 13%. Our findings report not only a higher rate of obesity generally, but also a higher rate of severe obesity among the obese patients.
A recent study of 215 patients with fibromyalgia reported that obesity in fibromyalgia adversely affected pain sensitivity to pressure, especially in the lower body, and altered sleep quality and quantity, physical strength, and flexibility (19). However, no associations were detected between self-reported symptoms and BMI, and no significant differences were found between groups in the FIQ scores and numerical rating of pain. Similarly, another study also did not find a significant association between BMI and pain (20). These studies did not subclassify the obese patients on the basis of the degree of obesity. Of note, the differences in self-reported symptoms in our study were primarily from the severely obese group, and the differences were not as apparent in other group comparisons. We found the higher BMI being associated with an increasing number of tender points, suggesting higher pain sensitivity, as has been noted previously (18, 19). The difference in the number of tender points was noted only in the severely obese group when compared with the nonobese group.
Our large sample size allowed us to classify and analyze the overweight, moderately obese, and severely obese groups separately, which is most likely the reason that our study showed differences not apparent in other studies in patients with fibromyalgia. The ability to examine differences in grade of obesity is a major strength of our study.
Our findings in QOL were similar to general population study reports in terms of severe obesity having significantly lower QOL scores, especially affecting physical component summary scores, than mental, social, and emotional aspects (7). QOL has been shown to be significantly lower in patients with fibromyalgia compared to the general US population (31), and our SF-36 scores were lower than the general population in all subscales (26). The association of symptom severity with severe or morbid obesity also has been noted in other conditions. Morbidly obese patients had significantly higher frequency of low back and other musculoskeletal pain than lean patients (32–34), and the lowest QOL scores occurred in the morbidly obese patients compared with other BMI strata (35, 36). Gastrointestinal symptoms, including abdominal pain, were also found to be more intense in morbidly obese patients (37).
We observed group differences in the FIQ depression subscale that were noted only between the severely obese patients and the nonobese patients in post hoc analysis. Although we found group differences in depression, our study was not designed to adequately assess depression. Our measure of depression was the FIQ depression subscale, rather than an independently validated depression-specific questionnaire (38–40), and its association needs further study.
It is not clear why and how a greater BMI is associated with increased fibromyalgia symptoms and decreased levels of QOL. Chronic pain and overweight and obesity likely have additive effects and may lead to decreased QOL and increased disability. A community-based twin registry study on chronic pain and obesity showed that overweight or obese twins were more likely to have fibromyalgia than normal-weight twins and that the associations can be partly related to familial and socioeconomic factors, as well as depression (21). There are likely diverse multiple factors playing a role in the association of chronic pain and obesity. Potential mechanisms that may explain the association between fibromyalgia and obesity include poorer sleep quality (41), deconditioning (18, 19), a higher level of pain receptors in fat tissue (18), alterations in the endogenous opioid system, elevated serum levels of proinflammatory cytokines (18, 19, 21), thyroid dysfunction (41), and dysregulation of the hypothalamic–pituitary–adrenal axis and an autonomic dysfunction (21), and increased mechanical loads associated with greater BMI (19). Although causal relationship is not clear between obesity and fibromyalgia, a higher rate of obesity in fibromyalgia patients than in the normal population may be caused by vicious circle of pain and physical inactivity.
Musculoskeletal symptoms, functional disability, and QOL associated with morbid obesity, as well as fibromyalgia symptoms in overweight and obese, have been shown to improve with weight reduction measures (32–34, 42, 43). Therefore, a fibromyalgia treatment program needs to incorporate weight loss strategies, including lifestyle changes with proper diet and increased physical activity. Referrals to medical and behavioral weight loss programs may need to be considered for patients with a BMI that exceeds 35.0 kg/m2.
This study has several limitations. First, the definition of obesity that we used was based on BMI. The waist-to-hip ratio may provide the best anthropometric measure to estimate abdominal fat (44). Second, pain sensitivity was measured through a manual tender point assessment and no objective measurement of pain sensitivity was included. Third, our measure of depression was the FIQ depression subscale, without including a validated depression-specific questionnaire, and our study was not designed to adequately assess depression. Fourth, the nonobese group included 15 patients who were underweight. However, the results were the same when we excluded them, and therefore we kept them in the study. Finally, this study was only based on patients with fibromyalgia. Future studies should also include comparison groups without fibromyalgia to evaluate any differences or similarities.
In conclusion, obesity is common in patients with fibromyalgia. A greater BMI, especially one that exceeds 35.0 kg/m2 (severe obesity), is associated with higher levels of fibromyalgia symptoms and pain, as well as lower levels of QOL.
All authors were involved in drafting the article or revising it critically for important intellectual content, and all authors approved the final version to be submitted for publication. Dr. Oh had full access to all of the data in the study and takes responsibility for the integrity of the data and the accuracy of the data analysis.
Study conception and design. Kim, Luedtke, Vincent, Thompson, Oh.
Acquisition of data. Kim, Luedtke, Oh.
Analysis and interpretation of data. Kim, Oh.