Underweight and overweight are associated with specific mortality patterns, but the disability burden of obesity is probably more important.
The growing prevalence of obesity, and the known association of overweight (as well as underweight) with higher all-cause mortality rates, led U.S. investigators to explore the relation between cause-specific mortality and body-mass index; they examined standardized national health-status surveys starting in 1971, with follow-up through 2004.
Underweight (BMI, <18.5 kg/m2) was
associated with significantly higher mortality from noncancer, noncardiovascular
disease (non-CVD) causes, whereas overweight (BMI, 25–<30) actually was
associated with significantly lower mortality from those causes. Neither
underweight nor overweight was associated with any difference in mortality from
cancer or CVD causes. However, obesity (BMI, 
30) was associated with significantly higher
mortality from CVD causes but not from cancer or noncancer, non-CVD causes. In
more detailed analyses, being overweight or obese was associated with higher
mortality from causes related to diabetes and kidney disease.
In a second study, weight and disability were
assessed in 9928 adults (age, 60) in 1988–1993 and in 1999–2004;
participants were evaluated for limitations in function (e.g., walking a quarter
mile, lifting 10 pounds, and rising from an armless chair) and activities of
daily living (ADL; e.g., eating and dressing). The prevalences of both
functional impairment and ADL limitations were higher among obese than among
normal-weight subjects in 1988–1993, and these gaps had widened by 1999–2004.
Comment: These results refine our understanding of the cause-specific effect of weight on mortality. However, associations between obesity, physical function, and disability are equally important. The burden appears to be larger today than in previous decades for the same level of obesity, presumably because people are now obese for longer portions of their lives. Editorialists argue that the effect of disability on quality of life shows that more attention should be paid to early lifestyle modification, behavior interventions, and public health and education outreach.
Published in Journal Watch General Medicine November 15, 2007
Flegal KM et al. Cause-specific excess deaths associated with underweight, overweight, and obesity. JAMA 2007 Nov 7; 298:2028.