Among its many rewards, eating a healthy diet might help protect against the development of chronic obstructive pulmonary disease, or COPD, according to a new study.

Based on more than 120,000 men and women followed for more than a decade, researchers calculate that those who ate a diet highest in whole grains, vegetables and nuts, and lowest in red meats and sugars were up to a third less likely to develop COPD – even if they smoked - than those who ate the worst diet.

"I think that we need to emphasize the role of diet in respiratory diseases, which is largely unknown by the general audience," lead author Dr. Raphaëlle Varraso, from the French National Institute of Health and Medical Research in Villejuif, told Reuters Health in an email.

"Respiratory health and lung function strongly predict general health status and all-cause mortality," she said.

COPD is an umbrella term for a group of progressive lung diseases that block the flow of air and cause breathing problems. They include emphysema, chronic bronchitis and some types of asthma.

According to the Centers for Disease Control and Prevention (CDC), about 15 million Americans have been diagnosed with COPD and it is the third leading cause of death in the U.S.

"The predominant risk factor for COPD in the developed world is cigarette smoking, but up to one-third of COPD patients have never smoked, thus suggesting that other factors are involved," Varraso said.

But relatively little attention has been paid to modifiable factors, aside from smoking, that might reduce the risk of developing COPD, including diet, she noted.

"As the lungs exist in a high-oxygen environment, it is reasonable to hypothesize that certain exposures can increase the burden of oxidants further," she added.

Varraso and her team used U.S. data on 73,000 women and 43,000 men who were part of long-term studies that tracked their lifestyles and medical histories between 1984 and 2000.

The researchers rated the participants’ eating habits based on the Alternate Healthy Eating Index 2010 (AHEI-2010), which is a measure of dietary quality based on current scientific evidence about the effects of nutrients on health risks. High scores on this index - developed at the Harvard School of Public Health as an alternative to the U.S. Department of Agriculture’s “food pyramid” - have been shown to be associated with a lower risk of major chronic diseases.

A better score also generally represents a diet that is high in vegetables, whole grains, polyunsaturated fats, nuts and omega-3 fatty acids, low in red and processed meats, refined grains and sugary drinks, and includes moderate alcohol consumption.

Those with the highest AHEI-2010 scores were 33 percent less likely to develop COPD than participants with the lowest diet scores, the study team reports in the journal BMJ.

The results held up even after the researchers accounted for other factors, such as tobacco use, exposure to second-hand smoke, weight, age and exercise habits.

The study does not prove cause and effect, however, said Dr. Norman H. Edelman, senior consultant for scientific affairs at the American Lung Association. "It only suggests that there may be a link."

Edelman, who was not involved in the study, added, "There has been evidence of this before, that one way to ameliorate lung disease is to eat a diet high in antioxidants. This study used a large database and suggests that diet may play a substantial role in lowering the risk."

But the most important preventive action for lung health is still smoking cessation, Edelman emphasized. "This study doesn't change that message," he said.

For those who would like to lower their risk of major chronic diseases, including COPD, Varraso pointed out that the AHEI guideline (bit.ly/RysZuA) is "quite easy" to follow.

But for people who already have COPD, the role of diet may be different, she noted. "In our study we only investigated the role of a healthy diet on the risk of COPD."

Varraso added that these study results should encourage clinicians to consider the potential role of the combined effect of foods in a healthy diet in promoting lung health.