2586 - The Effect of Body Mass Index On the Outcomes of Rheumatoid Arthritis

Wednesday, November 9, 2011: 9:15 AM
W196b (McCormick Place West)
Frederick Wolfe, National Data Bank for Rheumatic Diseases, Wichita, KS and Kaleb Michaud, National Data Bank for Rheumatic Diseases and University of Nebraska, Omaha, NE
Presentation Number: 2586

Background/Purpose: Body Mass Index (BMI) has a seemingly paradoxical effect on mortality in rheumatoid arthritis (RA), with the highest risk occurring in those with are underweight UW) (BMI 18.5 kg/m2) and a decreased risk in those who are overweight (OV) (BMI 25.0-29.9 kg/m2) or obese (OB) (BMI ³30.0 kg/m2) compared with those with normal BMI  (NW) (BMI 18.5-24.9 kg/m2). We explored the mechanism for this paradox and the role BMI plays in comorbidity and functional and quality of life outcomes.

Method: We assessed 24, 549 RA patients for up to 12 years using a semiannual questionnaire. Mortality data were obtained from the U.S. National Death Index. Hazard ratios were estimated with time varying Cox regression.

Result: At a mean age of 61.8 years (71.8% female), 65% were OW or OB. The overall hazard ratio for mortality indicated an increased mortality risk in UW and a protective effect for OW and OB (Table 1). BMI had a U shaped relation to age, with BMI increasing through age 50 and falling thereafter. We identified an interaction between age and BMI on the risk of mortality: under age 50, OB increased mortality risk by 61%, but over age 50 mortality in OW and OB was reduced by 29-37% (Table 1).  Regardless of BMI category, a 5-unit increase in BMI was associated with 26.2% (22.7, 29.8) increase in diabetes and a 34.7% (32.3, 37.3) increase in hypertension.

There was a U-shaped relation between all patient-reported clinical outcomes and BMI category. Four representative variables are shown in Figure 1. The "best" BMI for clinical outcomes, regardless of gender was 22-23. Compared with NW, the increase in annual total medical costs was UW $1151, OW $752, OB $3380.

%

H.R. (95% CI)

H.R. (95% CI)

H.R. (95% CI)

Age Group

All

All

50 Years

>50 Years

Underweight

2.1

2.13 (1.87, 2.44)

2.62 (1.11, 6.21)

2.46 (2.15, 2.81)

Normal weight

32.9

1.0

1.0

1.0

Overweight

32.1

0.81 (0.75, 0.88)

0.97 (0.60, 1.57)

0.71 (0.66, 0.77)

Obese

33.0

0.94 (0.86, 1.02)

1.61 (1.06, 2.44)

0.63 (0.58, 0.69)


Conclusion: Increased BMI leads to diabetes and hypertension, which are important predictors of mortality in RA. However, increased BMI itself is protective for mortality, except in patients less than 50 years of age. Overweight is not a direct risk factor for mortality, but influences clinical status and overall health. UW, OW and OB contribute to the severity of clinical measures and to increased costs.


Keywords: rheumatoid arthritis (RA)

Disclosure: F. Wolfe, None; K. Michaud, None.