Dietary influences on chronic obstructive lung disease and asthma: a review of the epidemiological evidence

The epidemiological evidence for a relationship between diet and indicators of asthma and chronic obstructive pulmonary disease (COPD) is evaluated. T he review focuses on the intake of Na, n-3 fatty acids, and antioxidant vit amins as well as fruit and vegetables. Experimental studies suggest that a high-Na diet has a small adverse effect on airway reactivity in asthma pati ents. However, observational studies provide no clear evidence that high Na intake has adverse effects on airway reactivity or asthma symptoms in open populations. n-3 Polyunsaturated fatty acids, which are present in fish oi ls, are metabolized into less broncho-constricting and inflammatory mediato rs than n-6 polyunsaturated fatty acids. Studies in the general adult popul ation suggest that a high fish intake has a beneficial effect on lung funct ion, but the relationship with respiratory symptoms and clinically-manifest asthma or COPD is less evident. Also, experimental studies in asthma patie nts have not demonstrated an improvement in asthma severity after supplemen tation with fish oil. Several studies showed a beneficial association betwe en fruit and vegetable intake and lung function, but the relationship with respiratory symptoms and the clinically-manifest disease was less convincin g. A similar pattern was found for vitamin C in relation to indicators of a sthma and COPD, but there are still conflicting results with respect to vit amin E and beta-carotene. In conclusion, the epidemiological evidence for a beneficial effect on indicators of asthma and COPD of eating fish, fruit a nd vegetables is increasing. However, the effectiveness of dietary suppleme ntation in open-population samples is often not demonstrated. Several unres olved questions are raised, which should be addressed in future studies on the relationship between diet and respiratory disease.