title: Mortality risk associated with underweight: a census-linked cohort of 31,578 individuals with up to 32 years of follow-up.
abstract: BACKGROUND
  In contrast to obesity, information on the health risks of underweight is sparse. We examined the long-term association between underweight and mortality by considering factors possibly influencing this relationship.
  
  
  METHODS
  We included 31,578 individuals aged 25-74 years, who participated in population based health studies between 1977 and 1993 and were followed-up for survival until 2008 by record linkage with the Swiss National Cohort (SNC). Body Mass Index (BMI) was calculated from measured (53% of study population) or self-reported height and weight. Underweight was defined as BMI < 18.5 kg/m2. Cox regression models were used to determine mortality Hazard Ratios (HR) of underweight vs. normal weight (BMI 18.5- < 25.0 kg/m2). Covariates were study, sex, smoking, healthy eating proxy, sports frequency, and educational level.
  
  
  RESULTS
  Underweight individuals represented 3.0% of the total study population (n = 945), and were mostly women (89.9%). Compared to normal weight, underweight was associated with increased all-cause mortality (HR: 1.37; 95% CI: 1.14-1.65). Increased risk was apparent in both sexes, regardless of smoking status, and mainly driven by excess death from external causes (HR: 3.18; 1.96-5.17), but not cancer, cardiovascular or respiratory diseases. The HR were 1.16 (0.88-1.53) in studies with measured BMI and 1.59 (1.24-2.05) with self-reported BMI.
  
  
  CONCLUSIONS
  The increased risk of dying of underweight people was mainly due to an increased mortality risk from external causes. Using self-reported BMI may lead to an overestimation of mortality risk associated with underweight.
authors.forename: Lucienne
authors.initials: L
authors.lastname: Roh
authors.forename: Julia
authors.initials: J
authors.lastname: Braun
authors.forename: Arnaud
authors.initials: A
authors.lastname: Chiolero
authors.forename: Matthias
authors.initials: M
authors.lastname: Bopp
authors.forename: Sabine
authors.initials: S
authors.lastname: Rohrmann
authors.affiliation: Institute of Social and Preventive Medicine (ISPM), University of Zurich, Hirschengraben 84, 8001 Zürich, Switzerland. david.faeh@ifspm.uzh.ch.
authors.forename: David
authors.initials: D
authors.lastname: Faeh
mesh_terms: D000328:Adult; D000368:Aged; D015992:Body Mass Index; D002423:Cause of Death; D019352:Censuses; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008875:Middle Aged; D009765:Obesity / Q000150:complications; D016016:Proportional Hazards Models; D012307:Risk Factors; D057566:Self Report; D013851:Thinness / Q000401:mortality*
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