Chronic obstructive pulmonary disease (COPD) is much more common in obese individuals ages 50 and older who have never smoked, according to a study that also shows that the odds of having COPD increases with the level of obesity.
Led by researchers at the University of Toronto in Canada, the study, “A Strong Graded Relationship between Level of Obesity and COPD: Findings from a National Population-Based Study of Lifelong Nonsmokers,” was published in the Journal of Obesity.
It is estimated that 15 million Americans have COPD. In most cases, the disease is caused by cigarette smoking; however, 23% of COPD patients have never smoked, and the cause of their disease is unknown.
Previous studies have suggested a possible link between COPD and obesity, which, for adults, is defined as having a body mass index (BMI) of 30 or higher.
“Surprisingly few studies have focused on never smoking COPD patients” Senyo Agbeyaka, one of the study’s lead authors, said in a press release. “We wanted to address this gap in the literature by examining which factors are associated with COPD among never smokers aged 50 and older.”
The team investigated the possible association between COPD and obesity in a nationally representative sample of non-Hispanic white individuals, ages 50 and older who had never smoked — 76,004 women and 37,618 men. The data were obtained from the 2012 Centers for Disease Control’s Behavioral Risk Factor Surveillance System.
Subjects were categorized as having normal weight (BMI less than 25 kg/m2), overweight (BMI between 25 and 29.99 kg/m2), with class 1 and 2 obesity (BMI between 30 and 39.99 kg/m2), or class 3 obesity (BMI of 40 kg/m2 or higher).
Researchers found a higher prevalence of COPD in individuals with higher BMIs.
“The prevalence of COPD increased from 2.5% in men and 3.5% in women who were of a healthy weight (BMI less than 25) to 7.6% in men and 13.4% in women who had a BMI of 40 or higher,” they wrote.
After statistically adjusting the results for factors that could potentially influence the prevalence of COPD including age, education, and income, a link to obesity was still found.
“The odds of COPD among women were 25% higher for those in the overweight category, twice as high for those in class I or II obesity, and four times higher for women who had class III obesity, in comparison with those with normal weight,” the researchers wrote.
Among men, the odds of COPD “were 71% higher for men with class I or II obesity, and 3-fold higher for men with class III obesity in comparison with men who were normal weight,” according to the study.
Interestingly, age and income were associated with higher odds of COPD. “In addition to obesity, older age and lower income were associated with COPD among both men and women,” said Lilia Fuller-Thomson, PhD, one of the authors of the study.
Furthermore, “among women, but not men, height and education level were negatively associated with COPD, but being married was associated with higher odds of COPD,” she said.
According to the team, one limitation of the study was that it only determined an association, but not whether obesity caused COPD, or if COPD predisposed patients to obesity.
Three plausible explanations for the strong association were suggested by the team: Either obesity causes “chest wall compression and impairs diaphragm movement”; the inflammation known to be associated with obesity causes or exacerbates COPD; or COPD symptoms result in decreased mobility and activity, which, in turn, contributes to a higher BMI.
“Unfortunately, the survey did not allow us to identify why older obese Americans who were never smokers had such a high prevalence of COPD. Future research is needed to investigate plausible mechanisms for this association, including the role of chronic inflammation associated with obesity and the impact of central obesity on respiratory system mechanics” said Kaitlyn Howden, a study co-author and an MD candidate at McMaster University.
These “findings highlight the importance of healthcare professionals routinely screening their older obese patients for COPD, even when the patients have no history of smoking” said Esme Fuller-Thomson, PhD, another lead author of the study.