title: An adequate threshold for body mass index to detect underweight condition in elderly persons: the Italian Longitudinal Study on Aging (ILSA).
abstract: BACKGROUND
  The present study aims at defining a body mass index (BMI) threshold for risk of being underweight in elderly persons on the basis of the BMI distribution in a large Italian population-based sample and on its ability to predict short-term mortality.
  
  
  METHODS
  At baseline (1992), BMI was obtained for 3110 (1663 males and 1447 females) persons aged 65-84 participating in the Italian Longitudinal Study on Aging (ILSA). BMI and risk factors (age, sex, education, smoking status, disability, and disease status) have been considered for their potential association with 4-year all-cause mortality. Information on vital status at 1995 was obtained for 2551 participants.
  
  
  RESULTS
  The fifth centile of BMI was well approximated by a value of 20 for both sexes. Also in both sexes, at a BMI value of 24 the a posteriori probability of death started to increase, doubling at a value of 22 for men and 20 for women. Crude mortality was 14.6% for men and 9.8% for women. The hazard ratios and confidence intervals (CIs) comparing mortality for each BMI two-unit class to the 26-28 class, after adjusting for confounding variables, showed significantly higher rates only for BMI values below 20 (2.9; 95% CI, 1.2-7.0), although a consistent increase in hazard ratio (1.6; 95% CI, 0.9-3.0) already appeared for the 20-22 BMI group.
  
  
  CONCLUSIONS
  Our study confirms that low BMI is an independent predictive factor of short-term mortality in elderly persons. A BMI value of 20 kg/m2 seems to be a reliable threshold for defining underweight elderly persons at high risk. Nevertheless, more careful clinical and nutritional management should also be applied to elderly persons with higher BMI values.
authors.affiliation: Department of Medical and Surgical Sciences, Division of Geriatrics, University of Padua, Italy. giuseppe.sergi@tin.it
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Sergi
authors.forename: Egle
authors.initials: E
authors.lastname: Perissinotto
authors.forename: Claudia
authors.initials: C
authors.lastname: Pisent
authors.forename: Alessandra
authors.initials: A
authors.lastname: Buja
authors.forename: Stefania
authors.initials: S
authors.lastname: Maggi
authors.forename: Alessandra
authors.initials: A
authors.lastname: Coin
authors.forename: Francesco
authors.initials: F
authors.lastname: Grigoletto
authors.forename: Giuliano
authors.initials: G
authors.lastname: Enzi
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000375:Aging / Q000502:physiology*; D015992:Body Mass Index; D002423:Cause of Death / Q000639:trends; D016001:Confidence Intervals; D003430:Cross-Sectional Studies; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007558:Italy / Q000453:epidemiology; D008297:Male; D011237:Predictive Value of Tests; D011379:Prognosis; D016016:Proportional Hazards Models; D016019:Survival Analysis; D015996:Survival Rate / Q000639:trends; D013851:Thinness / Q000175:diagnosis* / Q000401:mortality*