Obesity paradox debunked in COPD patients with BMI >40
The notion that overweight patients with COPD* seems to have a reduced risk of mortality vs those who are of normal weight, or that fat alters outcomes in obese patients – a phenomenon called “obesity paradox” – does not hold true if BMI is >40 kg/m2, a study has shown.
COPD patients with BMI >40 had a higher mortality rate (hazard ratio [HR], 1.36, 95 percent confidence interval [CI], 1.00-1.86) vs those with normal weight (BMI 20-25). The mortality risk was also higher in underweight patients (BMI <20; HR, 1.31, 95 percent CI, 1.04-1.64). [ATS 2018, abstract A7495]
Compared with the normal weight group, mortality was lower in the overweight group (BMI 25 –30; HR, 0.62) and the less severely obese groups (BMI 30 –35; HR, 0.75; and BMI 35 –40; HR, 0.85).
Given that many diseases result in wasting at the end of life, the perception that extra catabolic reserve can prolong survival makes intuitive sense. However, despite the plausibility of this hypothesis, the researchers did not find evidence of an obesity paradox in patients with BMI >40.
Previous studies have shown that overweight COPD patients have a better prognosis than leaner patients. A study by Franceso et al in 2018, for example, found that the obesity paradox is more evident in patients with severe bronchial obstruction, said Dr Emily Brigham from the Johns Hopkins University School of Medicine in Baltimore, Maryland, US who presented the current findings at the ATS 2018. By contrast, the weight-related mortality was similar between patients with mild-to-moderate obesity and the general population.
To fully elucidate the link, Brigham and her team sought to examine data from the double-blind, randomized controlled SUMMIT trial, on the use of fluticasone furoate and vilanterol in adults with moderate COPD and cardiac risk. A total of 16,485 adults from 43 nations, with histories of smoking at least 10 packs a day, were included in the analysis.
“Our results, combined with the work of others, suggest that BMI is an important factor [that] physicians should consider when evaluating mortality risk in COPD patients,” she said. “As expected, the majority of mortality was attributable to cardiovascular causes and this held true in all BMI categories.” However, whether the obesity paradox is directly related to excess fat is not very clear, Brigham added.
As to why the obesity paradox appeared not to exist in patients with higher BMI, Brigham had this to say: “Higher BMI is associated with a higher prevalence of a number of diseases that contribute to mortality, including metabolic disease and CVD … in these patients, the extremes of obesity and lung function is reduced – something that is particularly consequential in patients with COPD whose lung function is already compromised. It is reasonable to expect that at some threshold the positive effects of BMI in this population will be overwhelmed by the negative health consequences of obesity, as we see in the study.”
This, she said, has implication to practice. “I would have increased concern about mortality risk in a patient with moderate COPD and known CVD or risk factors, who is underweight or has a BMI >40. Nutrition and physical activity may be an important part of caring for this patient.”