Chronic Obstructive Pulmonary Disease: Nutritional Considerations

While the mechanism by which cigarette smoke causes COPD in some persons is unclear, a growing body of evidence supports the hypothesis that COPD is influenced by oxidative stress, inflammation, and an imbalance between protease and antiprotease activity.³ Antioxidants and fatty acids influence these processes and thus have theoretical roles in the prevention and treatment of COPD. However, most studies of specific nutrients and foods relate to COPD prevention, rather than treatment, and further research is necessary to establish their value. Of course, nutritional interventions, if shown to be clinically useful, must be used along with avoidance of smoking or other causative agents and with appropriate treatment.

The following dietary factors are under investigation for their possible roles in preventing COPD or affecting its course:

Fruits and Vegetables

Although cause and effect cannot be established from existing evidence, a number of studies have associated higher intakes of fruits and vegetables with a lower risk for COPD. In a population of smokers, eating at least 4 ounces of fruit and 3 ounces of vegetables daily was associated with a 50% lower COPD risk, compared with individuals who ate the least amounts of these foods.⁴ Similarly, a slower rate of decline in FEV1 was found in a general population with higher average intake of foods containing vitamin C.⁵

However, benefits of higher fruit and vegetable intakes on COPD risk were not apparent in a study of both smokers and nonsmokers.⁶ A British study found no association between average fruit intake and lung function (FEV1), but did find a decline in FEV1 in individuals whose fruit intakes decreased over time.⁷

The putative protective effects of these foods may be partly related to the antioxidant effects of carotenoids⁸ and flavonoids,⁹ and to replacement of the vitamin C that COPD patients lose as a result of a systemic oxidant/antioxidant balance imbalance.¹⁰ However, these mechanisms and effects are speculative only, and the effect of diets high in fruits or vegetables on the incidence or progression of COPD remains to be assessed in clinical trials.

Omega–3 Fatty Acids

In human subjects with COPD, supplementation with an omega–3–containing calorie supplement (400 cals/day) for 2 years significantly improved dyspnea and reduced the rate of decline in arterial oxygen saturation, compared with a group given an isocaloric supplement containing omega–6 fatty acids.¹¹ Other evidence indicates benefits of omega–3 fatty acid supplements on exercise capacity in patients with COPD, in comparison with those on placebo.¹² Additional controlled clinical trials are needed to determine if omega–3 fats reduce the incidence or rate of progression of COPD.

If omega–3 fatty acids influence COPD, the mechanism may relate to their antiinflammatory effects. Through competition for the lipoxygenase pathway, omega–3 fatty acids interfere with production of omega–6 fat–derived leukotrienes (eg, LTB4), which have proinflammatory, bronchoconstrictive effects.¹³

Vitamin E

Some observational studies have found protective effects of dietary (not supplementary) vitamin E intake on lung function.⁶ However, in the Alpha–Tocopherol Beta–Carotene Cancer Prevention Study involving over 29,000 subjects, neither alpha–tocopherol (50 mg/d) or beta carotene (20 mg/d) supplements lessened COPD symptoms, although high baseline blood levels of vitamin E were associated with a lower risk for COPD and dyspnea in smokers, compared with individuals who had the lowest levels.⁸ Clinical trials have not yet assessed the value of diets high in vitamin E for reducing COPD risk or decreasing its rate of progression.

The association between certain antioxidants and COPD derives some theoretical support from the fact that a deficiency of alpha–1 protease inhibitor leads to lung tissue breakdown and pulmonary emphysema. Blood vitamin E concentrations correlate positively with serum alpha–1 protease inhibitor levels in smokers.¹⁴

Maintenance of Adequate Body Weight

In several studies, lower than ideal bodyweight was associated with a greater risk for death from COPD,¹⁵ and a loss of fat–free mass appears to be an independent predictor of mortality in these patients.¹⁶ However, clinical trials have not yet established whether the associations between low body weight or lean body mass and COPD mortality are causal or incidental. Protein–calorie supplements do not appear to benefit most COPD patients. By some estimates, almost one in four patients with COPD is malnourished.¹⁷ Although nutritional supplements are commonly used to correct this condition, a review of existing evidence concluded that supplementation has no significant effect on anthropometric measures, lung function, or exercise capacity in COPD patients.¹⁸

Orders

Please see Basic Diet Orders chapter.

Nutritional supplements, if indicated and per recommendation of registered dietitian.

What to Tell the Family

COPD is preventable in most cases by not smoking or by quitting smoking early. As disease severity progresses, patients will need varying amounts of medications to reduce lung inflammation, dilate the bronchi, and reduce airway obstruction. Eventually, supplemental oxygen becomes necessary. The role of diet in preventing the progression of COPD is unclear.