Mortality risk associated with underweight: a census-linked cohort of 31,578 individuals with up to 32 years of follow-up

BMC Public Health. 2014 Apr 16;14:371. doi: 10.1186/1471-2458-14-371.

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Aged
  • Body Mass Index*
  • Cause of Death*
  • Censuses
  • Female
  • Follow-Up Studies
  • Humans
  • Male
  • Middle Aged
  • Obesity / complications
  • Proportional Hazards Models
  • Risk Factors
  • Self Report
  • Thinness / mortality*