Weight loss and a low body mass index (BMI) are associated with worse mortality outcomes among men with chronic obstructive pulmonary disease (COPD) in Japan, according to a new study.
Various studies have shown an association between low BMI (a ratio of weight to height) and worse mortality outcomes in people with COPD. However, a method to generalize these findings has been elusive, since most studies have focused specifically on underweight individuals.
Also, most studies have been conducted in the U.S. and Europe, and there are substantial population differences between these countries and elsewhere in the world. For instance, in the U.S., roughly one third of the population had a BMI of 30 kilograms per square meter (kg/m2) or higher in 2010 — a value generally considered the cutoff for obesity. In contrast, in the same year in Japan, about 3.3% of the population had a BMI of 30 kg/m2 or higher.
“In the present study, we investigated how low BMI and weight loss are associated with COPD mortality in a large prospective cohort of middle-aged Japanese men,” the researchers wrote.
The team specifically analyzed data from the Japan Collaborative Cohort Study for Evaluation of Cancer Risk (JACC) study. Initiated in the late 1980s, JACC collected data and followed up with patients for decades. The median follow-up period in this study was 19.1 years. Because COPD-related mortality was fairly rare among females, researchers focused their analyses on males.
In total, the study included data from 45,837 people, with more than 741,706 person-years of follow-up. (Person-years is a measure of the number of people participating in a study and the amount of time they were followed.) During follow-up, 268 people died due to COPD.
Compared to a reference group — those with a BMI of 20 kg/m2 or higher, but less than 22 kg/m2 — individuals who were underweight (a BMI less than 18.5 kg/m2) were about 3.24 times more likely to succumb to COPD.
Individuals with a BMI between 18.5 and 20 kg/m2 were about 68% more likely to die from COPD, whereas those with a BMI of 22 kg/m2 or higher were 42% less likely to die of COPD.
Additional analyses, in which early COPD-related deaths within five, 10, and 15 years of the original survey were excluded, found generally consistent results.
In other analyses, the researchers examined the relationship between weight change since age 20 and risk of death from COPD.
Compared to individuals whose weight did not change by more than 5 kg (about 11 pounds), those who lost 10 kg or more were at 3.34 times higher risk of COPD-related death. Similar to the BMI analyses, the findings did not generally change when early deaths, soon after the original survey, were excluded.
Other analyses indicated that weight loss was associated with worse COPD mortality across BMI groups; the highest risk of COPD-related mortality occurred in individuals with the lowest BMI and the most weight loss.
Notably, all analyses accounted for other relevant factors, such as age, alcohol intake, exercise habits, and other conditions like diabetes and high blood pressure.
“Our large-scale prospective community-based epidemiological study showed that lower BMI and weight loss are potential independent disease-specific markers for COPD mortality,” the researchers wrote. “Individuals who have lost more than 10 kg since the age of 20, and those with a BMI [less than] 18.5 kg/m2 had highest risk for mortality from COPD.”
The team speculated several possible explanations for this observation, such as the possibility that underweight people could be more susceptible to infections, or that low BMI and weight loss could be reflective of the effects of cigarette smoking. Of note, the majority of COPD mortalities observed in the group that was analyzed occurred in smokers.
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