SAN FRANCISCO -- Now add one more reason to eat plenty of fruits and vegetables: Their antioxidants seem to help protect lung function and may help prevent asthma, emphysema and chronic bronchitis, according to a new Cornell University study.
The beneficial effects of consuming high levels of antioxidants are significant. They are comparable to the difference in the lung function between a nonsmoker and a long-term smoker, the researchers reported. Antioxidants are substances, such as beta carotene and selenium, that work in different ways to protect cells from biochemical damage.
The researchers presented their findings at the Federation of American Societies for Experimental Biology (FASEB) meeting here today (April 18).
"Specifically, in terms of lung function as measured by how much air the lungs could expel, the difference between people with above-average levels of all the major antioxidants and those with below-average levels is about equivalent to the difference between the lung function of nonsmokers versus those who've smoked a pack a day for 10 years," said researcher Patricia Cassano, an epidemiologist in Cornell's Division of Nutritional Sciences.
However, the researchers urged caution in estimating the size of the effect from a single study and emphasized that further research is needed to better understand these associations.
The antioxidant beta carotene, a compound of carotene found in dark green, dark yellow and orange vegetables and fruits, was found to be dramatically less protective for smokers. And the heavier the smoker, the less protective the antioxidant. In fact, beta carotene offered almost no protection for heavy smokers.
The antioxidant selenium, however, which is found in meats, fish, cereals, dairy products, and Brazil and some other nuts, was shown to be more protective for smokers than nonsmokers. The antioxidants vitamin C and E were found to be equally protective for both groups. The beneficial effects of each antioxidant remained significant even when all the antioxidants were considered together.
The researchers' study was based on a population sample in the United States. But they found similar evidence of the protective effects of antioxidants in 69 counties in China. These findings were based on data from part of the China Project, a large epidemiological study of health, diet and disease, according to Cassano. Her fellow researcher is Guizhou Hu, a Chinese doctoral student at Cornell. Hu has the equivalent of an M.D. degree from Beijing Medical University and a master's degree in nutritional toxicology.
Lung function normally declines with age, and compromised lung function is a hallmark of chronic obstructive pulmonary disease (COPD), which includes chronic bronchitis, asthma and emphysema. COPD is the fifth leading cause of death in the United States, affecting 5 million people over age 55 and contributing to about 2 million hospitalizations a year.
Cigarette smoking is the principal risk factor for COPD, say the researchers, yet only 15 percent of cigarette smokers develop COPD. To try to figure out why, Hu and Cassano examined the 1988-1994 National Health and Nutritional Examination Survey of 18,162 randomly selected adults in the United States to see if dietary and blood serum antioxidants were associated with lung function and to see whether smokers and nonsmokers had similar effects.
Previous studies had suggested that beta carotene and other antioxidants might protect against lung cancer. Knowing the biology of COPD and following up on earlier reports, Cassano and Hu hypothesized that antioxidants also might protect lung function.
Their study is the first to report the effects of beta carotene and selenium on lung function, and the first and largest study to look at both the individual and joint effects of the major antioxidants on lung function.
Of the U.S. sample studied, 36 percent took supplements, although the data did not provide the details of supplement use, such as type, dose, duration of use or reason for use. The researchers speculate that the lack of detailed information on supplements could be one reason why they did not find a difference in lung function between those who took supplements and those who did not.
The researchers found that their analyses, when controlled for gender, age, body fat, race, income and cigarette smoking, provide powerful evidence "that antioxidant nutrients play a role in maintaining lung function in adults and suggest that the effects of the antioxidant component differ according to smoking status."
In the Chinese sample, the researchers found that those with higher levels of vitamin C in their diets had better lung function than others. The association of vitamin C and lung function did not differ among smokers and nonsmokers. Their China findings have been accepted for publication by the American Journal of Epidemiology.
The study was supported in part by a grant to Cassano from the National Heart, Lung and Blood Institute.