N° 17 | November 2007

Adolescent’s respiratory health may benefit from eating fruit and foods rich in n-3 fatty acids

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Diets with high consumption of foods rich in antioxidant and anti-inflammatory micronutrients may promote children’s optimal respiratory health. We have recently reported that adolescents with the lowest dietary intakes of antioxidant and anti-inflammatory micronutrients had lower pulmonary function and increased respiratory symptoms.

Adolescence is a period of rapid physical growth, yet adolescents often have poor dietary habits. Micronutrients, such as antioxidants, aid in lung growth and defenses; consequently, low dietary intake may result in lower attained lung function and increased respiratory symptoms, such as chronic cough, wheeze, and asthma.
We examined the association of dietary factors (fruit, vegetables, vitamins C and E, beta-carotene, retinol, n-3 fatty acids) with respiratory health in a cohort of 2,112 twelfth-grade students in 13 communities in the United States and Canada during the 1998 to 1999 school year. Students performed a standardized forced expiratory maneuver according to American Thoracic Society methods, using a rolling-seal spirometer (Spiroflow; PK Morgan; Andover, MA). Results were corrected to body temperature and pressure saturated with water. Students completed a standardized respiratory questionnaire patterned after the American Thoracic Society-Division of Lung Disease questionnaire, as well as a semiquantitative food frequency questionnaire designed for adolescent populations. We assessed the associations between dietary factors (including vitamin supplements) and lung function with linear mixed regression models, and respiratory symptoms with logistic regression using a generalized estimating equation adjusted for individual and group-level covariates.

We found that both lower dietary fruit and vitamin C intakes were associated with lower lung function compared with higher intakes. Low fruit intake (<0.25 serving a day) was associated with lower forced expiratory flow in one second (FEV1) (-1.3% of predicted; 95% confidence interval [CI], -2.4 to 0.2% of predicted), and low dietary vitamin C intake (<85 mg a day) was associated with lower forced vital capacity FVC (-1.3% of predicted; 95% CI, -2.4 to -0.2% of predicted). Low fruit intake was also associated with increased odds of chronic bronchitic symptoms (odds ratio [OR], 1.36; 95% CI, 1.03 to 1.73) and asthma (OR, 1.34; 95% CI 0.93 to 1.94) compared with higher intake. Low dietary n-3 intake (<5.2 mg/day) was associated with increased odds of chronic bronchitic symptoms (OR, 1.37; 95% CI 1.05 to 1.81), wheeze (OR, 1.34; 95% CI 1.06 to 1.69), and asthma (OR, 1.68; 95% CI 1.18 to 2.39) compared with higher intake.

Most of the adolescents in this cohort had dietary intakes of fruit, vegetables, vitamins, and n-3 fatty acids below the Institute of Medicine’s recommended dietary reference intakes (DRIs). Among these adolescents the median serving of fruit was 0.6 a day. Additionally, only 11% of the adolescents consumed five or more multivitamin tablets a week. Fruit is an important source of antioxidants, such as vitamin C and flavonoids, as well as fiber. Although vitamin supplementation can help meet the DRIs, it does not completely alleviate low fruit intake since flavonoids and fiber are not included. Also, there is evidence that suggests a synergistic biological effect of micronutrients that occurs with the consumption of whole foods, such as fruit.

Adolescents often have dietary intake of important nutrients below levels recommended for health promotion. This may affect the attainment of optimal lung function. Although the lower pulmonary function associated with lower dietary fruit and vitamin C intakes in our study was not likely to have a functional impact on current respiratory health, it suggests that these adolescents may not attain their potential maximum lung function. Our study suggests chronic cough and wheeze are associated with low dietary micronutrient intakes. Both symptoms and lower maximum lung function may be associated with airway remodeling and later impairment of adult lung function. These factors may have long-term consequences because lower lung function in adults has been associated with increased morbidity and premature mortality. Prevention of the onset of smoking in this age group is a primary objective. However, promoting the consumption of fruit and foods rich in n-3 fatty acids may protect respiratory health in rapidly growing adolescents.

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