Dietary n-3 polyunsaturated acids and smoking-related chronic obstructive pulmonary disease.

Background: Fish contain n-3 polyunsaturated fatty acids, principally eicosapentaenoic acid and docosahexaenoic acid, which are known to interfere with the body's inflammatory response and may be of benefit in chronic inflammatory conditions.
Methods: We studied the relation between the dietary intake of n-3 fatty acids and chronic obstructive pulmonary disease (COPD) in 8960 current or former smokers participating in a population-based study of artheroscierosis. Intake of fatty acids was estimated with a dietary questionnaire. The presence of COPD was assessed by a questionnaire on respiratory symptoms and by spirometry. Three case definitions of COPD were used: symptoms of chronic bronchitis (667 subjects), physician-diagnosed emphysema reported by the subject (185 subjects), and spirometrically detected COPD (197 subjects).
Results: After control for pack-years of smoking, age, sex, race, height, weight, energy intake, and educational level docosahexaenoic acid was inversely related to the ris of COPD in a quantity-dependent fashion. The adjusted odds ratio for the highest quartile was 0.66 for chronic bronchitis (95 percent confidence interval, 0.52 to 0.85; P<0.001 for linear trend across the range of intake value), 0.31 for physician-diagnosed emphysema (95 percent confidence interval, 0.18 to 0.52; P for liner trend, 0.003), and 0.50 for spirometrically detected COPD (95 percent confidence interval, 0.32 to 0.79; P for linear trend, 0.007).
Conclusion: A high dietary intake of n-3 fatty acids may protect cigarette smokers against COPD.