Antioxidant micronutrients for cystic fibrosis lung disease

Shamseer L, Adams D, Brown N, Johnson JA, Vohra S

Published Online:

December 8, 2010

Antioxidant micronutrients may be a worthwhile addition to current treatment in cystic fibrosis. They may offset oxidant damage in the lungs resulting from constant infection. Since people with cystic fibrosis have trouble absorbing fat, they have low levels of two fat-soluble antioxidants - vitamin E and β-carotene. This review examined the effects of vitamins E and C, β-carotene and selenium on CF lung disease.

We found five trials to include in the review, but only three trials with a total of 87 participants had data available for analysis. We looked at the primary outcomes of lung function and quality of life; our secondary outcomes were oxidative stress, inflammation, body mass index, days on antibiotics and adverse events during supplementation. There is evidence both for and against supplementing antioxidant micronutrients for cystic fibrosis lung disease. There was no improvement in lung function, but levels of antioxidants in the blood improved with supplementation. The evidence also showed that quality of life (no specific aspect stated) decreased in groups taking supplements. Antioxidant supplementation in cystic fibrosis is not yet recommended beyond routine care. Larger trials looking at important clinical effects are needed.

Abstract (click to read)

Background:

Airway infection leads to progressive damage of the lungs in cystic fibrosis (CF), partly due to oxidative stress. Supplementation of antioxidant micronutrients (vitamin E, vitamin C, ß-carotene and selenium) may help maintain an oxidant-antioxidant balance. Current literature suggests a relationship between oxidative status and lung function.

Objectives:

To synthesize existing knowledge of the effect of vitamin C, vitamin E, ß-carotene and selenium in CF lung disease.

Search strategy:

The Cochrane CF and Genetic Disorders Group CF Trials Register, PubMed, CINAHL and AMED were searched using detailed search strategies. We contacted authors of included studies and checked reference lists of these studies for additional, potentially relevant studies.

Last search of CF Trials Register: 09 September 2010.

Selection criteria:

Randomized controlled trials and quasi-randomized controlled trials of people with CF with explicitly stated diagnostic criteria, comparing vitamin E, vitamin C, ß-carotene and selenium (individually or in combination) to placebo or standard care.

Data collection and analysis:

Two authors independently selected trials, extracted data and assessed risk of bias. We contacted trialists to obtain missing information. Primary outcomes are lung function and quality of life; secondary outcomes are oxidative stress, inflammation, body mass index, days on antibiotics and adverse events during supplementation. If meta-analysed, studies were subgrouped according to combined or single antioxidant supplementation.

Main results:

Four randomized controlled trials and one quasi-randomized controlled trial were included; only three trials (87 participants) presented data suitable for analysis. Based on two trials, there was no significant improvement in lung function; one trial indicated significant improvement in quality of life favouring control, mean difference -0.06 points on the quality of well-being scale (95% confidence interval -0.12 to -0.01). Based on two trials, selenium-dependent glutathione peroxidase enzyme significantly improved in favour of combined supplementation, mean difference 1.60 units per gram of haemoglobin (95% CI 0.30 to 2.90) and selenium supplementation, mean difference 10.20 units per gram of haemoglobin (95% CI 2.22 to 18.18). All plasma antioxidant levels, except vitamin C, significantly improved with supplementation.

Authors' conclusions:

There appears to be conflicting evidence regarding the clinical effectiveness of antioxidant supplementation in CF. Based on the evidence, antioxidants appear to decrease quality of life and oxidative stress; however, few trials contributed data towards analysis. Further trials examining clinically important outcomes and elucidation of a clear biological pathway of oxidative stress in CF are necessary before a firm conclusion regarding effects of antioxidants supplementation can be drawn.

This record should be cited as:

Shamseer L, Adams D, Brown N, Johnson JA, Vohra S. Antioxidant micronutrients for lung disease in cystic fibrosis. Cochrane Database of Systematic Reviews 2010, Issue 12. Art. No.: CD007020. DOI: 10.1002/14651858.CD007020.pub2

Assessed as up to date:

November 8, 2010

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Primary Review Group:

Cystic Fibrosis and Genetic Disorders Group

Health topics:

Gastroenterology > Cystic fibrosis > Nutrition

Genetic disorders > Cystic fibrosis > Nutrition

Lungs & airways > Cystic fibrosis > Nutrition

Complementary & alternative medicine > Gastroenterology > Cystic fibrosis

Complementary & alternative medicine > Genetic disorders > Cystic fibrosis