An expanding waistline may be a risk factor for chronic obstructive pulmonary disease, according to a recent study.

COPD is a progressive disease that makes it hard to breathe. The disease gets worse over time.

Researchers found that excessive belly fat and low physical activity are linked to progression of the disease in people with COPD, but it is not known whether these modifiable factors are linked to new cases.

"We observed a stronger positive relation with abdominal body fat than with total body fat and COPD," researcher Dr. Gundula Behrens said in a statement.

For the study, a team of researchers looked at the relationship of waist and hip circumference, body mass index (BMI) and physical activity levels to new cases of COPD in more than 113,000 men and women in the United States between the ages of 50 and 70 years who did not have COPD, cancer or heart disease at the beginning of the study.

During the 10-year follow-up period, COPD developed in 3648 people. Participants with a large waist circumference (110 cm or over in women and 118 cm or over in men) had a 72 percent increased risk of COPD.

"In particular, overweight as measured by BMI emerged as a significant predictor of increased risk of COPD only among those with a large waist circumference," Behrens said.

Researchers also found that a large waist was a robust predictor of COPD in smokers as well as in people who had never smoked.

People with a large hip circumference and who were physically active at least 5 times a week were 29 percent less likely to experience COPD. Exercise can reduce inflammation, oxidative stress and enhance healing. Underweight people had a 56 percent increased risk of COPD. Possible reasons include malnutrition and reduced muscle mass leading to increased COPD susceptibility and progression through inflammatory processes and impaired lung repair capacity.

"Our findings suggest that next to smoking cessation and the prevention of smoking initiation, meeting guidelines for body weight, body shape and physical activity level may represent important individual and public health opportunities to decrease the risk of COPD," researchers said.

The findings were recently published in the Canadian Medical Association Journal.