Smoking is the primary cause of chronic obstructive pulmonary disease in the US, accounting for 80-90% of all cases. For the remaining 10-20%, it is believed exposure to air pollution, secondhand smoke and genetic factors are involved. But in a new study published in The BMJ, researchers suggest an unhealthy diet could be a contributing factor.
Symptoms include shortness of breath during day-to-day activities, chronic cough, wheezing, frequent respiratory infections, excessive mucus production, fatigue and blueness in the lips or fingernails.
COPD is estimated to affect around 12.7 million adults aged 18 and over in the US. It was responsible for 134,676 deaths in the US in 2010, making it the third leading cause of death in the country.
While smoking is known to be the main cause of COPD, the study authors - from France and the US - say little research has looked at what other modifiable risk factors play a role. "Diet is one such factor," they note. "Prospective data on the association between diet and the risk of COPD remain scarce, compared with the extensive literature on cardiovascular diseases or cancer."
With this in mind, the team assessed the effects of diet on the risk of COPD among 73,228 women who took part in the Nurses' Health Study from 1984 to 2000, and 47,026 men who took part in the Health Professionals Follow-Up Study from 1986 to 1998.
COPD risk reduced by a third with a healthy diet
At the beginning of each study, all participants were required to complete a food frequency questionnaire and a health questionnaire, which disclosed information on weight, physical activity, smoking, medical history and other risk factors.
- While around 12.7 million adults in the US have been diagnosed with COPD, almost 24 million have evidence of impaired lung function, suggesting COPD is underdiagnosed
- Female smokers are almost 13 times more likely to die from COPD than women who have never smoked, while smoking men are 12 times more likely to die from the condition than those who have never smoked
- In 2010, COPD cost the US around $49.9 billion.
Follow-up questionnaires - which also gathered information on any newly diagnosed medical conditions - were completed every 2 years thereafter.
The researchers used the Alternate Healthy Eating Index 2010 (AHEI-2010) to measure the participants' diet quality. A higher AHEI-2010 score represents a healthy diet with a high intake of vegetables, whole grains, polyunsaturated fats, nuts and omega-3 fatty acids, a low intake of red and processed meats, refined grains and sugary drinks, and moderate alcohol consumption.
During the follow-up of both studies, there were 167 new cases of COPD diagnosed in men and 723 new cases diagnosed in women.
The researchers found that participants with the highest AHEI-2010 scores were a third less likely to develop COPD, compared with participants with the lowest scores, suggesting a healthy diet may reduce the risk of developing COPD.
These results remained even after the team accounted for participants' body mass index (BMI), smoking status, ethnicity, age and other potentially influential factors.
Commenting on their findings, the authors say:
"A high AHEI-2010 dietary score was associated with a lower risk of newly diagnosed COPD, a novel finding that supports the importance of diet in the pathogenesis of COPD.
Although efforts to prevent COPD should continue to focus on smoking cessation, these prospective findings support the importance of a healthy diet in multi-interventional programs to prevent COPD."
They add that clinicians should consider the role an individual's diet may play in lung health. They hypothesize that antioxidants in a healthy diet may be behind the protective effect against COPD.
"As the lungs exist in a high oxygen environment, it is reasonable to posit that certain exposures (and local inflammation) can further increase the burden of oxidants," they note. "The balance between these potentially toxic substances and the protective actions of antioxidant defenses, including those derived from diet, may play a role in the loss of lung function over time and the eventual development of COPD."
The team notes that the study is subject to some limitations. For example, they note that participants in the study were all health professionals. As such, they say the findings may not be applicable to the general population due to potential differences faced in health awareness, socioeconomic status and smoking behavior.
In addition, they note that the majority of participants were non-Hispanic white, which may limit the application of their findings to other racial/ethnic populations.
In November last year, Medical News Today published a spotlight feature that investigated whether the stigma surrounding COPD affects treatment for patients with the disease.