Body Mass Index and Fatigue Severity in Chronic Fatigue Syndrome

Transcription

1 Body Mass Index and Fatigue Severity in Chronic Fatigue Syndrome Ellen A. Schur, MD Carolyn Noonan, MS Wayne R. Smith, PhD Jack Goldberg, PhD Dedra Buchwald, MD ABSTRACT. Background: It is uncertain how much fatigue is related to weight in patients with chronic fatigue syndrome (CFS). Objective: To assess the association of body mass index (BMI) and fatigue in CFS patients. Methods: Consecutive patients seen in a referral-based specialty clinic were eligible if they met CFS criteria and had completed required measures. Fatigue measures were the vitality subscale of the Medical Outcomes Short-Form 36 and the global fatigue index from the Multidimensional Assessment of Fatigue. Results: In women, there was no relationship between BMI and vitality subscale or global fatigue index scores (P = 0.99 and P = 0.44). For men, vitality subscale scores significantly decreased as BMI increased (P = 0.02). Ellen A. Schur, Carolyn Noonan, and Dedra Buchwald are affiliated with the Department of Medicine, University of Washington, Seattle, WA. Wayne R. Smith is affiliated with the Department of Psychiatry and Behavioral Science, University of Washington, Seattle, WA. Jack Goldberg is affiliated with the Department of Epidemiology, University of Washington, Seattle, WA. Address correspondence to: Ellen A. Schur, Harborview Medical Center, 325 Ninth Avenue, Box , Seattle, WA ( ellschur@u.washington.edu). This study was supported in part by grant U19 AI38429 from the National Institute of Allergy and Infectious Disease. Journal of Chronic Fatigue Syndrome, Vol. 14(1) 2007 Available online at by The Haworth Press, Inc. All rights reserved. doi: /j092v14n01_07 69

2 70 JOURNAL OF CHRONIC FATIGUE SYNDROME Conclusions: In CFS patients, the prevalence of obesity was low despite risk factors for weight gain. Fatigue severity and BMI were unrelated in women with CFS, but this relationship may differ for men. doi: /j092v14n01_07 [Article copies available for a fee from The Haworth Document Delivery Service: HAWORTH. address: <docdelivery@haworthpress.com> Website: < by The Haworth Press, Inc. All rights reserved.] KEYWORDS. Chronic fatigue syndrome, fibromyalgia, fatigue, weight INTRODUCTION Severe, disabling fatigue is the hallmark of CFS. Prior research has shown that fatigue (1-3) and bodily pain (3,4) are increased in individuals who are overweight or obese. The relationship between overweight or obesity and increased subjective fatigue is especially strong in women (1,5,6). In addition, when patients have a chronic disease and are obese, they report more fatigue and lower energy levels (5). However, in fibromyalgia patients, there was no increased fatigue in overweight and obese subjects, despite more functional difficulties (7). TheextentthatweightcontributestofatigueinCFSisunknown,asisthe prevalence of overweight or obesity in CFS patients. To address these questions, we conducted a cross-sectional analysis of the association between BMI and fatigue severity in a well-defined cohort of patients with CFS. METHODS Patients and Setting. We included all adults seen at an academic referral center between August 1996 and July 2003 for the evaluation and treatment of chronic fatigue. Patients were not required to meet CFS criteria to be evaluated. All data collection involved in this study was approved by the University of Washington Institutional Review Board. Informed consent was obtained from all patients. Weight. BMI (kg/m 2 ) was calculated based on measured weight and height obtained at the index visit. Weight was classified according to guidelines published by the National Institutes of Health: underweight (BMI < 18.5 kg/m 2 ), normal weight (BMI kg/m 2 ), overweight

3 Original Research 71 (BMI kg/m 2 ), class I obesity (BMI kg/m 2 ), class II obesity(bmi kg/m 2 ),andclassiiiobesity(bmi > 40kg/m 2 )(8). Chronic Fatigue Syndrome, Psychiatric Diagnoses, and Fibromyalgia. CFS was diagnosed according to the 1994 case definition (9); fatigue and symptom criteria were determined by structured questionnaire administered prior to the patient s index visit. In accordance with the Centers for Disease Control and Prevention guidelines, patients were excluded from a CFS diagnosis for medical conditions, either active or previously diagnosed, whose presence or incomplete resolution might explain their fatigue as well as for a BMI > 45 kg/m 2 (9). Likewise, patients were excluded from the diagnosis if we documented lifetime melancholic or psychotic depression, bipolar disorder, schizophrenia, eating disorders, or alcohol and substance abuse within 2 years of the onset of their fatigue (9). Diagnoses were derived from the National Institutes of Mental Health Diagnostic Interview Schedule Version III-A, a structured interview, administered by a trained lay interviewer, that assigns current and lifetime psychiatric diagnoses based on the Diagnostic and Statistical Manual-III-R criteria(10,11). Fibromyalgia was diagnosed by history and physical examination criteria (12). Measures of Fatigue. The vitality subscale of the Medical Outcomes Short-Form General Health Survey is a 4-item subscale measuring fatigue and energy (13). Higher scores indicate less fatigue (range 0-100). The Short Form-36 and its subscales have high reliability and validity in diverse patient populations, including those with chronic fatigue, pain (14-16), and obesity (2,3,5). Prior analyses of our clinic sample revealed an adequate internal stability for the vitality subscale (Cronbach s = 0.74) (15). The Multidimensional Assessment of Fatigue is a 16-item instrument that measures the severity, distress, functional impact, and frequency of fatigue during the past week. Responses are used to create a global fatigue index with scores ranging from 1 (no fatigue) to 50 (severe fatigue). The reliability and validity of the Multidimensional Assessment of Fatigue has been demonstrated in adults with rheumatoid arthritis (17). It has excellent internal stability (Cronbach s = 0.93), concurrent validity with the Profile of Mood States fatigue subscale (r = 0.78), and divergent validity with its vigor subscale (r = 0.60) (17). Statistical Analysis. Descriptive statistics for continuous variables were calculated as mean values; frequency tables were computed for categorical variables. We used correlation analyses to assess the unadjusted association of fatigue severity, as measured by the Short Form-36 and Multidimensional Assessment of Fatigue, with weight and BMI. Linear

4 72 JOURNAL OF CHRONIC FATIGUE SYNDROME regression analyses were used to examine the association of fatigue severity and BMI after adjusting for potential confounding variables. All covariates included in the regression models were chosen a priori. Correlation results are presented as r-values and regression results show adjusted means and 95% confidence intervals for each BMI category. Statistical tests for the linear regression models were overall tests for trend. Analyses were stratified by sex and carried out using the SAS 8.2 software package (SAS Institute, Cary, NC). RESULTS A total of 187 patients with CFS met mandatory inclusion criteria of valid measurements for all variables considered in the analysis (listed in Table 1). These patients did not differ significantly from the 15 patients excluded due to missing data in demographic, clinical, or weight variables (data not shown). Among 215 additional patients with valid measurements who did not meet CFS criteria, only one was excluded solely for a BMI > 45 kg/m 2. Patient characteristics are shown in Table 1. In brief, 81% of patients were female and 95% were Caucasian. On average, patients had completed some education beyond high school (mean years ). As reported in other studies of CFS (15,18), fibromyalgia was more common in women than men (27% vs. 6%, P 0.01), but no other differences by gender were present. The mean BMI for the entire sample was 26.4 (SD 5.4). Among women, 55% had BMI 25 kg/m 2, and 22% were obese. Two-thirds of the men had a BMI 25 kg/m 2 and 30% were obese. On average, selfreported weight change was a gain of 6.2 kg since illness onset (mean 7.5 years). However, the degree of weight gain varied between men and women (men = 4.6 kg vs. women = 6.6 kg) and the amount and direction of weight change varied widely between individuals (range, 50 kg loss-34 kg gain). As anticipated, patients scores revealed severe fatigue (Table 1). Correlation between the vitality subscale and BMI was 0.03 (P = 0.73) for women and 0.44 (P = 0.01) for men. The correlation between the global fatigue index and BMI was 0.04 (P = 0.64) for women and 0.10 (P = 0.57) for men. Correlations of fatigue severity with weight and BMI were similar. Therefore, we focused our adjusted analyses on fatigue and BMI only.

5 Original Research 73 TABLE 1. Characteristics of patients with CFS. Characteristic Women Men All n = 151 (81%) N = 36 (19%) n = 187 Demographic Age, mean years ( SD) 43.8 (10.4) 41.0 (10.5) 43.3 (10.5) Caucasian (%) Education, mean years ( SD) 15.1 (2.4) 15.3 (2.5) 15.1 (2.4) Weight BMI, mean kg/m 2 ( SD) 26.1 (5.5) 27.7 (4.8) 26.4 (5.4) Weight change since illness onset, 6.6 (11.0) 4.6 (7.6) 6.2 (10.5) mean kg ( SD)* Underweight, % Normal weight, % Overweight, % Class I obesity, % Class II obesity, % Class III obesity, % Clinical Illness duration, mean years Meets fibromyalgia criteria, % current nonexclusionary psychiatric disorder, % Global fatigue index, 40.5 (6.5) 38.5 (8.4) 40.1 (6.9) mean score ( SD) Vitality subscale, mean score ( SD) 12.3 (12.4) 15.6 (16.6) 12.9 (13.3) *By self-report, 8 women and 2 men missing from observations. Underweight (BMI 18.5 kg/m 2 ), normal weight (BMI kg/m 2 ), overweight (BMI kg/m 2 ), class I obesity (BMI kg/m 2 ), class II obesity (BMI kg/m 2 ), and class III obesity (BMI 40 kg/m 2 ). A BMI 45 kg/m 2 is exclusionary for CFS. P 0.01 for difference between women and men. SD = Standard Deviation. We used linear regression to examine the association between fatigue and BMI after adjusting for potential confounders. Table 2 shows that, in women, adjusted mean vitality subscale and global fatigue index scores for class II obesity patients indicated worse fatigue, but these trends were not significant (P = 0.99 and P = 0.44). For men, adjusted mean vitality

6 74 JOURNAL OF CHRONIC FATIGUE SYNDROME TABLE 2. Adjusted mean fatigue severity score and 95% confidence intervals by BMI category* and sex in patients with CFS. Fatigue Measure Women Men Mean 95% CI P-value Mean 95% CI P-value Short Form-36 vitality subscale Underweight 11.2 ( ) Normal weight 9.3 ( ) 28.2 ( ) Overweight 12.2 ( ) (0-28.7) 0.02 Class I obesity 12.6 ( ) 8.1 (0-28.6) Class II obesity 7.1 (0-15.5) 10.3 (0-31.5) MAF, global fatigue index Underweight 42.7 ( ) Normal weight 43.4 ( ) 37.0 ( ) Overweight 41.2 ( ) ( ) 0.76 Class I obesity 40.8 ( ) 39.4 ( ) Class II obesity 44.6 ( ) 36.0 ( ) *Underweight (BMI 18.5 kg/m 2 ), normal weight (BMI kg/m 2 ), overweight (BMI kg/m 2 ), class I obesity (BMI kg/m 2 ), and class II obesity (BMI kg/m 2 ). Adjusted for age, race, years of education, illness duration, and presence of fibromyalgia and nonexclusionary psychiatric conditions. Linear regression test for trend in fatigue severity score and BMI. Lower scores indicate more fatigue. Higher scores indicate more fatigue. Values for men were inestimable because no men were underweight. MAF = Multidimensional Assessment of Fatigue. CI = Confidence Interval. subscale scores significantly decreased from 28.2 to 10.3 as BMI increased (P = 0.02). The trend in mean global fatigue index score for men did not reach statistical significance (P = 0.76). DISCUSSION We found that CFS patients seen in our specialty clinic were not excessively overweight or obese despite being ill for, on average, 8 years. Compared to published US norms (19), rates of overweight and obesity were slightly higher among our small sample of men and comparable for our women during the time period our data were obtained. For example, in the NHANES, the prevalence of obesity among non-hispanic whites was 20.3% for men and 22.9% for women; these rates increased to

7 Original Research % and 30.1% by (19). It is difficult to contextualize our findings as weight has rarely been reported in studies of CFS or other fatigued populations. A small study of bone density in young women with CFS reported that mean body weights did not differ from healthy controls (20). However, in a study of women with fibromyalgia of whom 91% were fatigued 28.4% were overweight, and rates of class I, II, and III obesity were 19.4%, 9.5%, and 3.3%, respectively (7). Rates of overweight in our CFS patients were similar, but obesity appeared to be less common. This finding does not reflect exclusion based on morbid obesity as only one patient who otherwise met criteria for CFS criteria was excluded solely due to BMI > 45 kg/m 2. Our data suggest that, despite suffering from a longstanding, debilitating illness, and previously documented low activity levels (21,22), CFS patients were not excessively overweight or obese. In the majority of our analyses, we found that fatigue levels in CFS patients were unrelated to BMI or weight. However, this relationship may differ for men. In our small group of male patients, reported fatigue as measured by the vitality subscale worsened at higher weights. This appears to primarily be due to normal weight men reporting the least severe fatigue levels of all patients enrolled in the study. This finding should be considered preliminary because of the small numbers of men in the study and the fact that it was not replicated by analyses of the global fatigue index scores. Among women with CFS, BMI did not appear to contribute to the experience of fatigue. This is in contrast to previous research showing worse fatigue at high BMIs (2,3,5) and in women (1,5,6). Our results are consistent with findings in patients with fibromyalgia (7). This suggests that the severe fatigue suffered by CFS patients is of a different origin unrelated to weight, and recent findings of polymorphisms in genes associated with the hypothalamic-pituitary axis support this hypothesis (23,24). This study has several limitations. First, the severity of patients symptoms may have prevented detection of further worsening of fatigue at higher BMI; such a floor effect may have limited our ability to demonstrate an association. Likewise, the negative result may reflect inadequate sensitivity of our measures to clinically relevant changes in fatigue. Second, we cannot address the role of lifestyle factors such as diet or physical activity in explaining our observations, as standardized and concurrent data on these parameters were unavailable. Third, our study had a relatively small sample size, especially of obese patients, which may explain why trends for increased fatigue in class II obesity in

8 76 JOURNAL OF CHRONIC FATIGUE SYNDROME female patients did not reach statistical significance. Finally, we included only patients seen in a referral clinic meeting strict criteria for CFS. Thus, our results may not generalize to patients seen in other settings, or with fatigue of lesser duration or severity. To our knowledge, this study is the first to assess the relationship between BMI and fatigue in CFS patients. In a clinical population that is often sedentary and even bed bound (21), the absence of excessive weight gain is both intriguing and encouraging. Our findings also suggest that recommendations to lose weight based solely on the desire to ameliorate fatigue may not be warranted. Areas for further research include assessing the relationship of fatigue and weight in larger samples of men, longitudinal work on weight change over the course of the illness, and assessments of lifestyle and nutritional factors. REFERENCES 1. Chen MK. The epidemiology of self-perceived fatigue among adults. Prev Med 1986; 15(1): Brown WJ, Mishra G, Kenardy J, Dobson A. Relationships between body mass index and well-being in young Australian women. Int J Obes Relat Metab Disord 2000; 24(10): Fontaine KR, Bartlett SJ, Barofsky I. Health-related quality of life among obese persons seeking and not currently seeking treatment. Int J Eat Disord 2000; 27(1): Stewart AL, Brook RH. Effects of being overweight. Am J Public Health 1983; 73(2): Katz DA, McHorney CA, Atkinson RL. Impact of obesity on health-related quality of life in patients with chronic illness. J Gen Intern Med 2000; 15(11): McIlvenny S, DeGlume A, Elewa M, Fernandez O, Dormer P. Factors associated with fatigue in a family medicine clinic in the United Arab Emirates. Fam Pract 2000; 17(5): Yunus MB, Arslan S, Aldag JC. Relationship between body mass index and fibromyalgia features. Scand J Rheumatol 2002; 31(1): National Heart Lung and Blood Institute. Clinical Guidelines on the Identification, Evaluation and Treatment of Overweight and Obesity in Adults. The Evidence Report. Bethesda, MD: National Institutes of Health, Public Health Service, U.S. Department of Health and Human Services; NIH Publication No Fukuda K, Straus SE, Hickie I, Sharpe MC, Dobbins JG, Komaroff A. The chronic fatigue syndrome: a comprehensive approach to its definition and study. International Chronic Fatigue Syndrome Study Group. Ann Intern Med 1994; 121(12): Robins LN, Helzer JE. Diagnostic Interview Schedule (DIS): Version III-A. St. Louis, MO: Washington University School of Medicine, 1985.

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