title: Underweight is a risk factor for atrial fibrillation: A nationwide population-based study.
abstract: BACKGROUND
  Obesity is a well-known risk factor for development of atrial fibrillation (AF). However, the impact of underweight on AF has not been previously recognized. We sought to determine the risk of AF in subjects with underweight in this study.
  
  
  METHODS
  We analyzed clinical data from a total of 132,063 individuals with the age of 40years or older who received health care checkups arranged by the national insurance program between 2003 and 2004. Newly diagnosed nonvalvular AF was identified using claim data during a median follow-up duration of 9.0years.
  
  
  RESULTS
  The mean body mass index (BMI) of patients was 23.9kg/m(2), and 3,323 individuals (2.5%) were classified as being underweight (BMI <18.5kg/m(2)). During the study period, 3,237 individuals (2.5%) developed AF. There was a U-shaped relationship between BMI and AF occurrence: Each 1.0kg/m(2) increase of BMI above 20kg/m(2) was associated with a 6% increased risk of AF (p<0.001), while each 1.0kg/m(2) lower BMI below 20kg/m(2) was associated with a 13% increased risk of AF (p<0.001) after multivariable adjustment. Underweight was significantly associated with 23% increased risk of AF, while obesity classes I and II were with 26% and 120% increased risk of AF, respectively. Excess risk of AF in the underweight was independent of thyroid disease, chronic lung disease, or history of malignancy, and was not attributable to cigarette smoking, low socioeconomic status, excessive physical activity, or heavy alcohol consumption.
  
  
  CONCLUSIONS
  BMI has a U-shaped relationship with the risk of AF. Underweight was an independent risk factor for AF independent of confounding factors such as chronic lung disease and malignancy. These findings suggest that underweight is associated with biological effects that contribute to the development of AF.
authors.affiliation: Department of Cardiology, Cardiovascular Center, Seoul National University Bundang Hospital, Seongnam, Republic of Korea.
authors.forename: Si-Hyuck
authors.initials: SH
authors.lastname: Kang
authors.affiliation: Division of Cardiology, Department of Internal Medicine, Seoul National University Hospital, Seoul, Republic of Korea. Electronic address: choiek17@snu.ac.kr.
authors.forename: Eue-Keun
authors.initials: EK
authors.lastname: Choi
authors.affiliation: Department of Biostatistics, College of Medicine, The Catholic University of Korea, Seoul, Republic of Korea.
authors.forename: Kyung-Do
authors.initials: KD
authors.lastname: Han
authors.affiliation: Division of Cardiology, Department of Internal Medicine, Seoul National University Hospital, Seoul, Republic of Korea.
authors.forename: So-Ryoung
authors.initials: SR
authors.lastname: Lee
authors.affiliation: Division of Cardiology, Department of Internal Medicine, Seoul National University Boramae Medical Center, Seoul, Republic of Korea.
authors.forename: Woo-Hyun
authors.initials: WH
authors.lastname: Lim
authors.affiliation: Department of Cardiology, Cardiovascular Center, Seoul National University Bundang Hospital, Seongnam, Republic of Korea.
authors.forename: Myung-Jin
authors.initials: MJ
authors.lastname: Cha
authors.affiliation: Department of Cardiology, Cardiovascular Center, Seoul National University Bundang Hospital, Seongnam, Republic of Korea.
authors.forename: Youngjin
authors.initials: Y
authors.lastname: Cho
authors.affiliation: Department of Cardiology, Cardiovascular Center, Seoul National University Bundang Hospital, Seongnam, Republic of Korea.
authors.forename: Il-Young
authors.initials: IY
authors.lastname: Oh
authors.affiliation: Division of Cardiology, Department of Internal Medicine, Seoul National University Hospital, Seoul, Republic of Korea.
authors.forename: Seil
authors.initials: S
authors.lastname: Oh
mesh_terms: D000328:Adult; D000368:Aged; D001281:Atrial Fibrillation / Q000453:epidemiology*; D015992:Body Mass Index; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D009765:Obesity / Q000453:epidemiology; D056910:Republic of Korea / Q000453:epidemiology; D012307:Risk Factors; D013851:Thinness / Q000453:epidemiology*
keywords: Atrial fibrillation; Body mass index; Epidemiology; Risk factors