In the general
population, obesity is an established risk factor for reduced life
expectancy, independent of smoking status [22]. Paradoxically,
epidemiological studies have shown that the patients with
advanced COPD who are overweight or mildly to- moderately
obese have a survival advantage compared with underweight
patients [23]. This ‘‘obesity paradox’’ has also been described
in other chronic diseases (chronic heart failure, rheumatoid
arthritis, and chronic renal disease) but the protective mechanisms
are unknown [24]. It is noteworthy that this reduced risk
of mortality was not observed in obese patients with milder
COPD [25] and that subgroups of COPD patients with more
severe obesity are at a greater risk of death due to respiratory
failure than normal weight COPD [26].