FRIDAY, March 6 (HealthDay News) -- Being big around the middle can put the squeeze on your lungs, according to French researchers who studied more than 120,000 people.

It was already known that abdominal obesity (waist circumference greater than 35 inches for women and greater than 40 inches for men) was associated with diabetes, hypertension, cardiovascular disease and numerous other health problems collectively known as metabolic syndrome.

This study found that abdominal obesity is also strongly associated with decreased lung function -- independent of smoking history, body-mass index (BMI), sex and other factors.

"We found a positive independent relationship between lung function impairment and metabolic syndrome due mainly to abdominal obesity," wrote lead author Dr. Natalie Leone, of the French National Institute for Health and Medical Research.

She suggested a number of ways that excess abdominal fat may limit or decrease lung function.

"This association may result from the mechanical effects of [abdominal] obesity and/or the metabolic effects of adipose [fat] tissue. Abdominal obesity may mechanically affect the diaphragm and chest wall compliance with decreased lung volume," Leone said.

She also noted that the amount of fat tissue in the body increases levels of pro-inflammatory markers and decreases levels of anti-inflammatory markers.

"Adipose tissue may act as an additional source of systemic inflammation," she wrote.

The researchers also identified a strong interaction between metabolic syndrome and smoking status. Current and former smokers were more likely to have lung function impairment than people who never smoked.