Researchers at the American Thoracic Society's 97th International Conference stated that eating fruits and vegetables seems to reduce the risk of developing some types of lung disease and could even improve lung function.
"There is extensive evidence from studies over the last 10 to 15 years that a diet rich in fruits and vegetables is beneficial to lung health," said Carol Trenga, Ph.D., Research Scientist in the Department of Environmental Health at the University of Washington in Seattle, who moderated a press panel on diet and lung health.
"The most compelling evidence is linked to fruits high in vitamin C, which are associated with improved lung function in the general population of adults and children."
Eating moderate portions of fruit and vegetables can reduce the risk of chronic obstructive pulmonary disease (COPD) in smokers, another study said. The researchers found that eating one-and-a-half pieces of fruit or a large tablespoonful of vegetables every day can protect against COPD (emphysema and chronic bronchitis).
Louise Watson, MSc, who did the research at the University of Southampton, United Kingdom, was curious to know why about 15% of smokers develop COPD, while many smokers do not. Her study included current and former smokers with and without COPD who completed a questionnaire about their food intake over the previous year.
The 266 participants had at least 10 pack years of smoking history (meaning they had smoked at least 20 cigarettes per day, every day per year). She figured out that vegetable intake of one or more portions per day (equivalent to one or more tablespoons) cut the risk of the disease nearly in half. Eating one-and-a-half pieces of fruit or more per day also significantly protected against COPD.
Watson pointed out that the best way for smokers to prevent lung disease and heart disease is to quit smoking. "Regarding diet, this research suggests that a moderate intake of fruit and vegetables may be protective against developing COPD and therefore the diet ought to contain at least one-two portions per day of fruit and one portion per day of vegetables as part of a healthy and varied diet," she said.
Eating a diet high in fruits, particularly apples and tomatoes, may protect against respiratory illness, according to another study presented at the conference. Researchers at the University of Nottingham, United Kingdom, studied the relationship between diet and self-reported wheeze, doctor-diagnosed asthma and lung function in 2,633 adults.
They discovered that eating five or more apples per week or at least three tomatoes a week were most strongly associated with increased lung function. Eating a lot of apples and tomatoes also reduced the risk of wheezing.
The study's lead researcher, Sarah Lewis, Ph.D., notes that it is not known what nutrients in apples and tomatoes protect against lung problems. "The likelihood is that any effect is due to the concerted action of all the nutrients in apples and tomatoes, especially the antioxidants that are particularly rich in the peel of apples and contribute to the coloring of tomatoes," she said. "Antioxidants may work by protecting the airways against the insult of tobacco smoke and other atmospheric pollutants."
Lewis said they don't know yet whether the beneficial effects of these foods acts in the same way throughout a person's life or whether the effects are limited to, or stronger in, particular periods such as early in life or in childhood.
"To try to sort this out we have been conducting a nine-year follow-up of this population, and so far we have found some evidence that eating these fruits may have some protective effect against long-term decline in lung function," she said. "This suggests, though by no means conclusively, that it is not a once and for all effect in childhood, and that eating these types of food in adulthood continues to effect our lung health. However, how much and for how long remains unknown."
The moderator, Dr. Trenga, said she believes enough evidence exists from many studies supporting the beneficial effects of a diet containing modest amounts of fruits and vegetables on lung health.
"Although more controlled trials are needed with specific nutrients to clearly identify the most beneficial substances and clarify some of the mechanisms of action, there is reasonable scientific evidence indicating a positive effect of dietary supplementation of certain nutrients in high risk populations.
"It is both good public health policy and preventive medical practice to advocate increased consumption of fruits and vegetables, encouraging the goal of five servings a day. It is also reasonable to suggest modest supplementation with vitamin C (250-500 mg twice/day) and vitamin E (up to 400 IU per day), in at-risk populations as a complementary therapy after considering the specific needs of the individual patient.
"These levels are considered to be very safe and have other health benefits in addition to potentially improving lung health."