Vienna, Va. A new study from the National Institutes of Health (NIH) reports that eating foods rich in fiber and flavonoids — found most abundantly in apples — may reduce your chronic productive cough and other respiratory symptoms.

Researchers analyzing whether diet might impact chronic productive cough — commonly experienced in persons with chronic respiratory conditions such as chronic obstructive pulmonary disease (COPD) — reported that high consumption of fiber and fruits, specifically apples, appears to be associated with a lower incidence of cough. Their findings suggest that promoting a high-fiber, high-flavonoid diet may help reduce chronic respiratory symptoms, both in smokers and non-smokers.

Reporting in the August issue of the peer-reviewed American Journal of Respiratory and Critical Care Medicine, Dr. Lesley Butler of NIH and her colleagues noted they found an inverse association between fiber consumption and the incidence of productive cough — that is, the more fiber consumed, the lower the reported incidence of cough. Fiber consumption appears to reduce the incidence of cough even in non-smokers, as well as smokers. While fruits, vegetables and grains are the top dietary sources of fiber, an association was found only for non-citrus fruit — the higher the consumption of fruit, the lower the reported incidence of cough plus phlegm. (Source: Butler, L.M., Koh W-P. et al. American Journal of Respiratory and Critical Care Medicine August 2004; vol. 170, no. 3, pp 279-287. The paper can be accessed online at http://ajrccm.atsjournals.org/cgi/content/abstract/170/3/279.)

Of all the foods examined, the most significant relationship was seen with apples. The association for apples was also seen independent of fiber, suggesting that other apple nutrients besides fiber may offer lung protection. Researchers suggested that antioxidant phytonutrients such as flavonoids may be at work.

Apples are one of the top dietary sources for fiber and flavonoids. One medium, tennis ball-sized apple contains five grams of fiber, and apples are the top fruit source of flavonoids.

"Cough and phlegm are frequently associated with [COPD], which may be caused by oxidative stress-mediated inflammation and tissue damage in the lung," wrote Butler and her colleagues. "Fruits and vegetables are the major food sources of antioxidants that may protect the lung from oxidative stress. We observed the strongest inverse dose-response associations for apples, pears and grapes." That means the more of these foods that were eaten, the greater the benefit was, with the benefit increasing in direct correlation with the amount of fruit consumed.

"Our findings suggest that flavonoids may play a crucial role," Butler and colleagues wrote. "Flavonoids may protect the lung on the basis of their antioxidant and anti-inflammatory properties."

The prospective cohort study involved 571 persons aged 45-74 reporting a productive cough, who were identified from the ongoing Singapore Chinese Health Study, a large 49,140-person epidemiological study that began in 1993. The study was supported by NIH and the National Institute of Environmental Health Services.

Diet May Impact Chronic Lung Disease

According to the American Lung Association (ALA), COPD is the fourth leading cause of death in the United States, claiming the lives of 107,146 Americans annually. ALA reports that 80 to 90 percent of COPD cases are caused by smoking; other leading causes are second-hand smoke and exposure to air pollutants.

"Our data from the Singapore Chinese Health Study provide evidence that promoting a diet high in sources of fiber and flavonoids, such as fruit and soy, may be an important contribution to primary prevention strategies for chronic respiratory symptoms, both in smokers and nonsmokers," the authors wrote.

Latest Studies to Link Apples, Lung Health

The NIH study is the latest of many to suggest we might breathe easier — literally — by eating apples.

• Researchers at the University of Groningen in the Netherlands reported that smokers eating moderate amounts of fruits and vegetables — and particularly apples — cut their risk of developing COPD nearly in half.
• In January 2000, researchers at London's St. George's Hospital also documented a possible link between apples and lung function.
• Researchers at the University of Hawaii and Finland's National Public Health Institute both linked apple consumption with a reduced risk of lung cancer in separate studies published in 2000 and in 1997, respectively.

Note to editors:

• This and other USApple consumer and health news releases are available at http://www.usapple.org/media/newsreleases/index.cfm. A summary of recent apple health research is available at http://www.usapple.org/educators/research/index.cfm.