The current study shows that metabolic syndrome is also associated with impaired lung function. Further, abdominal obesity -- compared to the other factors -- is most tightly linked to the lung function impairment.
Researchers in France recruited more than 120,000 people. They performed a physical exam with blood tests, and checked demographic information, smoking status, measured their waistlines, and tested their lung function.
Those with metabolic syndrome were about 1.4 times more likely to have lung function impairment. But researchers were surprised by the findings in people with abdominal obesity.
People with excess belly fat were twice as likely to have impaired lung function. This was true even if their weight was normal. Previously, experts believed only severe obesity contributed to decreases in lung function.
Researchers aren't sure what the relationship is between big bellies and bad breathing. The effect could be mechanical: a large belly might restrict the diaphragm and make it harder for lungs to expand. Or, the extra fat could increase inflammation in the body, somehow harming the lungs.
Abdominal obesity is defined most often as a waistline greater than 35 inches for women, and 40 inches for men. More than half of American adults today have bellies this size or larger. The average French man in the study had a 35-inch waist, at an average age 46. The average French woman's waist was about 30 inches at the same average age.
The study appears in the American Journal of Respiratory and Critical Care Medicine.