DIETARY ANTIOXIDANTS IMPROVE LUNG FUNCTION

BILTHOVEN, THE NETHERLANDS-Men with higher intakes of fruits and vegetables rich in antioxidants (vitamins C and E and b-carotene) have better lung function than do those with lower intakes, according to a European population-based study published in a recent issue of Thorax.1 Although it is not yet clear whether these findings can be extrapolated to women, the study results suggest that dietary modulation may benefit at least some patients with chronic obstructive pulmonary disease.

The study included more than 2,300 men from Finland, Italy, and the Netherlands. In all three countries, men who consumed more than the median amounts of fruits and vegetables had a higher forced expiratory volume (FEV) compared with men whose diets were wanting in those types of comestibles. Specifically, high FEV was associated with high vitamin E intake in Finland, high fruit intake in Italy, and high b-carotene intake in the Netherlands, according to the study findings. The results with the combined intake of vitamins C and E and b-carotene were, however, not as perspicuous.

Nevertheless, overall, FEV was higher in the men whose fruit and vegetable intakes were above the median than in those in whom the intake of both food groups was below the median; this remained true even after the analysis was adjusted for smoking, body mass index, and alcohol intake. Adjustment for energy intake reduced the observed between-group differences but did not render them statistically insignificant. "The difference in FEV ranged from 110 mL to 169 mL before and from 53 mL to 118 mL after energy adjustment," noted the authors.

The Thorax study is not the first to demonstrate a relationship between dietary antioxidants in fruits and vegetables and lung function, but the outcomes of previous studies have been inconsistent owing to variations in the outcomes studied (eg, whether intake or plasma levels of antioxidants were studied, and whether only dietary intake or intake of supplementary antioxidants was also included).

WIDE VARIATIONS IN FOOD INTAKE

Dietary intake varied widely in the three study countries. Daily intake of vegetables, for instance, averaged 176 g in the Netherlands, 79 g in Finland, and 53 g in Italy. Mean intake of fish was 39 g in Finland, 21 g in Italy, and 17 g in the Netherlands. Fruit intake was somewhat more consistent across the three countries: 191 g in Italy, 174 g in Finland, and 152 g in the Netherlands.

The current study found no clear relationship between intake of fish (which contain omega-3 fatty acids) and pulmonary function. It did, however, show that bread intake was positively associated with FEV in all three countries. (An association between whole grain consumption and chronic diseases had been described previously, the authors noted.) One of the proposed mechanisms of action is through the antioxidant capacity of several components of whole grains, including vitamin E, but the Thorax study did not differentiate between white and whole-grain breads. The study also found that intake of potatoes, margarine, or oils-foods containing vitamins C or E-was not associated with FEV.

Several epidemiologic studies have demonstrated a relationship between diet and chronic obstructive pulmonary disease. "Antioxidants and foods rich in antioxidants, such as fruit, are thought to protect the airways against oxidant-mediated damage," the authors stated.

Associations between intakes of vitamin C and fruit, levels of antioxidants, and pulmonary function are fairly consistent; the effects of vitamin E and b-carotene on pulmonary function are not as well established-findings have been variable. The authors point out that "a small amount of misclassification of dietary intake may . . . have a substantial effect on the studied associations. Furthermore, one dietary factor with antioxidant capacity may not be a good indicator of the antioxidant's status in the lungs related to diet. It may thus be better to study the joint effect of several antioxidant factors on pulmonary function," which is why they chose to study different antioxidants in different groups of middle-aged men in three different countries.

STUDY DESIGN

As part of a larger epidemiologic study (the Seven Countries Study2), data on diet and FEV, measured by spirometry, were collected from a total of more than 3,000 men living in Finland, Italy, and the Netherlands between 1959 and 1970. Complete data on diet, pulmonary function, and potential confounders were available for 1,248, 1,386, and 691 men in Finland, Italy, and the Netherlands, respectively; data on pulmonary function were missing for 29, 149, and 28 subjects, respectively. Men with missing lung function data had a lower energy intake than those with a complete record in all three countries, and their energy-adjusted intakes of fruit and/or vitamin C tended to be lower.

Food intake was estimated using the cross-check dietary history method, which provided information about the usual food consumption pattern for 6 to 12 months preceding the interview. Nutrient intake was assessed using computerized versions of the local food tables from the three countries. Fruit consumption was defined as intake of all fresh and canned fruits and fruit juices. Vegetable consumption did not include intake of potatoes or legumes. High antioxidant intake was defined as intake of vitamins C and E and b-carotene above the median. Likewise, high and low intakes of fruits and vegetables were defined as intake of both types of food above or below the median.

STUDY LIMITATIONS

The authors noted that since this study was cross-sectional, a temporal relationship between diet and pulmonary function could not be established. Furthermore, due to the relatively small number of subjects in the different countries, especially the Netherlands, the power of the study may not be sufficient to detect small effects. Finally, although the investigators adjusted for cigarette smoking, a residual confounding by smoking is possible.

The investigators also noted differences in spirometric measurements (FEV in 0.75 seconds or 1 second) among the three countries, such that FEV levels cannot be compared across the countries. "Comparisons within the three separate countries are, however, valid," the authors said.

-Margaret A. Inman

References
1. Tabak C, Smit HA, Räsänen L, et al. Dietary factors and pulmonary function: a cross-sectional study in middle-aged men from three European countries. Thorax. 1999;54:1021-1026.
2. Keys A, Aravantis C, Blackburn H. Epidemiological studies related to coronary heart disease: characteristics of men aged 40-59 in seven countries. Acta Med Scand. 1967;460(suppl):1-392.