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P760 The risk of inflammatory bowel disease based on body mass index and waist circumference: a nationwide population-based study

S. Park*1, J. Chun1, K-D. Han2, H. Soh1, E. A. Kang1, H. J. Lee1, J. P. Im1, J. S. Kim1

1Seoul National University College of Medicine, Department of Internal Medicine and Liver Research Institute, Seoul, South Korea, 2College of Medicine, The Catholic University of Korea, Department of Biostatistics, Seoul, South Korea

Background

The relationship between the occurrence of inflammatory bowel disease (IBD) and the indicators of obesity and underweight including body mass index (BMI) and waist circumference (WC) still remains unclear. The aims of this study was to determine the risk of developing IBD based on the baseline levels of BMI and WC, and changes in body weight.

Methods

We conducted a nationwide population-based cohort study using claims data from the National Health Insurance (NHI) database in Korea. A total of 19,356,194 individuals who attended a national health check-up program from 2011 to 2012. Among them, 10,699,693 (55.3%) individuals who had not undergone a national health check-up 2 years before the baseline, who had been diagnosed with IBD previously or had insufficient data were excluded in this study. Study endpoint was newly diagnosed IBD including Crohn’s disease (CD) and ulcerative colitis (UC) during the follow-up to 2017. Obesity, overweight and underweight was defined based on the Asia-Pacific BMI classifications as follows: obesity, ≥25 kg/m2; overweight, 23 to 24.9 kg/m2; and underweight, < 18.5 kg/m2.

Results

A total of 8,656,501 participants were enrolled in the study. Among them, obese, overweight and underweight individuals were 2,864,672 (33.1%), 2,197,148 (25.4%), and 289,580(3.3%), respectively. During the follow-up, IBD were newly detected in 267 (0.09%) of underweight, 2,365 (0.07%) of normal weight, 1,412 (0.06%) of overweight, 1,438 (0.06%) of class I obese, and 127 (0.04%) of class II obese groups. Compared with normal weight, the risks of developing CD was significantly higher in underweight (adjusted HR by age and sex, 1.73; 95% CI, 1.35–2.21), but lower in overweight (adjusted HR, 0.61; 95% CI, 0.52–0.72), class I (adjusted HR, 0.51; 95% CI, 0.43–0.60) and II obese groups (adjusted HR, 0.47; 95% CI, 0.32–0.71), respectively. The risk of developing UC was also significantly higher in underweight (adjusted HR, 1.31; 95% CI, 1.13–1.52), but lower in overweight (adjusted HR, 0.90; 95% CI, 0.83–0.97), class I (adjusted HR, 0.77; 95% CI, 0.72–0.83) and II obese groups (adjusted HR, 0.55; 95% CI, 0.45–0.67), respectively, compared with normal weight group. BMI and WC at baseline showed inverse linear associations of risk for developing IBD. Moreover, the interval decrease in body weight within 2 years significantly increased the risk for developing CD, but not UC, in proportion to the percentage of weight loss.

Conclusion

Underweight increased the risk for developing IBD, but overweight and obesity reduced the risk of IBD compared with normal weight. BMI and WC was inversely associated with risk of IBD. Physicians would be aware of the potential for developing CD in individuals experiencing unintentional weight loss.