Abstract

Background

Many people with atopic eczema are reluctant to use the most commonly recommended treatments because they fear the long‐term health effects. As a result, many turn to dietary supplements as a possible treatment approach, often with the belief that some essential ingredient is 'missing' in their diet. Various supplements have been proposed, but it is unclear whether any of these interventions are effective.

Objectives

To evaluate dietary supplements for treating established atopic eczema/dermatitis.

Evening primrose oil, borage oil, and probiotics are covered in other Cochrane reviews.

Search methods

We searched the following databases up to July 2010: the Cochrane Skin Group Specialised Register, the Cochrane Central Register of Controlled Trials (CENTRAL) in The Cochrane Library, MEDLINE (from 2005), EMBASE (from 2007), PsycINFO (from 1806), AMED (from 1985), LILACS (from 1982), ISI Web of Science, GREAT (Global Resource of EczemA Trials) database, and reference lists of articles. We searched ongoing trials registers up to April 2011.

Selection criteria

Randomised controlled trials (RCTs) of dietary supplements for the treatment of those with established atopic eczema/dermatitis.

Data collection and analysis

Two authors independently screened the titles and abstracts, read the full text of the publications, extracted data, and assessed the risk of bias.

Main results

We included 11 studies with a total of 596 participants. Two studies assessed fish oil versus olive oil or corn oil placebo. The following were all looked at in single studies: oral zinc sulphate compared to placebo, selenium versus selenium plus vitamin E versus placebo, vitamin D versus placebo, vitamin D versus vitamin E versus vitamins D plus vitamin E together versus placebo, pyridoxine versus placebo, sea buckthorn seed oil versus sea buckthorn pulp oil versus placebo, hempseed oil versus placebo, sunflower oil (linoleic acid) versus fish oil versus placebo, and DHA versus control (saturated fatty acids of the same energy value). Two small studies on fish oil suggest a possible modest benefit, but many outcomes were explored. A convincingly positive result from a much larger study with a publicly‐registered protocol is needed before clinical practice can be influenced.

Authors' conclusions

There is no convincing evidence of the benefit of dietary supplements in eczema, and they cannot be recommended for the public or for clinical practice at present. Whilst some may argue that at least supplements do not do any harm, high doses of vitamin D may give rise to serious medical problems, and the cost of long‐term supplements may also mount up.

Author(s)

Fiona J Bath‐Hextall, Claire Jenkinson, Rosemary Humphreys, Hywel C Williams

Abstract

Plain language summary

Dietary supplements for established atopic eczema in adults and children

Eczema is a skin condition characterised by an itchy, red rash, which affects 5% to 20% of people worldwide. There is no cure, but many treatments can help improve the skin's condition, making life easier. In those for whom these treatments do not work well or who fear their long‐term effects, there is often a belief that either something in their diet, or something missing in their diet, is making their eczema worse.

This review looked at the following dietary supplements (products which add ingredients to a diet): fish oil, zinc, selenium, vitamin D, vitamin E, pyridoxine (vitamin B6), sea buckthorn oil, hempseed oil, and sunflower oil. 

Three commonly used dietary supplements (evening primrose oil, borage oil, and probiotics) are currently the subject of other Cochrane reviews (Boehm 2003; Boyle 2008).

We looked for trials comparing supplements with placebo (dummy). We included 11 randomised controlled trials (596 participants) when it was clear that the children or adults taking part had atopic eczema. In reviewing the trials, the main outcomes we looked for were evidence of improvement in the symptoms of eczema, such as itching or loss of sleep, in the short‐term (i.e. six weeks). In the longer term, we wanted to see evidence of a reduced need for treatment for the eczema or a reduction in the number of flares. We also looked for evidence of any general improvement in the eczema and in individual symptoms. 

Overall, we found no convincing evidence that taking supplements improved the eczema of those involved. In general, studies were small with low numbers of participants and of poor quality in terms of the way they were run. Two trials of fish oil did find slight improvement for the participants in terms of the degree of itchiness and quality of life. However, these trials had small numbers, which means they had little chance of finding real differences if they did exist. That is why larger trials are needed before any recommendations can be made. We found no evidence of adverse (harmful) effects in those who took part in the trials. People sometimes think that supplements can at least do no harm; however, high doses of vitamin D, for example, can cause serious medical problems, and the safety of dietary supplements should not be assumed. The cost of supplements can also mount up. 

Author(s)

Fiona J Bath‐Hextall, Claire Jenkinson, Rosemary Humphreys, Hywel C Williams

Reviewer's Conclusions

Authors' conclusions 

Implications for practice 

Disappointingly, we have not found any convincing evidence of the benefit of dietary supplements in eczema. It is not possible for us to claim that all of the supplements that were examined in this review are not effective, because all of the studies were of low quality and most were much too small (underpowered) to exclude even relatively moderate treatment benefits.

Whilst this review cannot exclude the possibility that dietary supplements may play a role in improving eczema, the absence of positive evidence means that they cannot be recommended to the public or for clinical practice at present.

Two small studies on fish oil suggest a possible modest benefit, but many outcomes were explored, and a convincingly positive result from a much larger study with a publicly registered protocol is needed before clinical practice can be influenced. In addition, one study comparing vitamin D plus E to placebo found a significant improvement of SCORAD at the end of treatment where vitamin D or vitamin E alone had not. This study was small, and a larger study is needed to confirm these results. There is also a real need to look closely at adverse events. It is unclear if these small but statistically significant differences are clinically worthwhile in the absence of better information on the scales used.

Whilst it is possible that some may argue that at least supplements do not do any harm, high doses of vitamin D may give rise to serious medical problems, and the cost of long‐term supplements may also mount up.

Implications for research 

The grounds for recommending further clinical trial research in this field are limited. Whilst it is true that public interest in supplements of various sorts for chronic diseases is quite high, the main lack of anything positive to date may reflect poorly‐designed, poorly‐reported, and underpowered studies. There needs to be a stronger theoretical, biological, epidemiological, and experimental rationale before recommending further research in this area. Much attention has already been focused on evening primrose oil with no clear sign of benefit (Williams 2003), although another Cochrane review will address this specific topic (Boehm 2003). Given the presence of at least some positive secondary/tertiary outcomes in two of the studies that have explored fish oil, and that there is at least some good theoretical basis why they might play a role in dampening down the inflammatory pathway, a much larger placebo‐controlled and well‐designed study might be worthwhile. Although recent evidence has suggested that increased vitamin D intake may play a role in altering immune responses (Schwalfenberg 2011) and in protecting atopic diseases, such as asthma, we are not aware of any convincing role in eczema prevention or treatment (Miyake 2010; Miyake 2011). There is, however, some emerging data on the role of vitamin D in possibly modifying immune responses in eczema (the sunshine hypothesis, Searing 2010), and one recent study has shown a possible link between eczema severity and low vitamin D levels.

Another study has shown that vitamin D supplementation could reverse some of the defects in the innate immune system associated with atopic eczema, such as the capacity to increase the production of broad spectrum antimicrobial peptides like cathelicidin, which may in turn decrease the risk of secondary infections (Hata 2008).

It is also worth pointing out that many of the "placebos" used substances, such as olive oil, which might not be inert, thereby, reducing the chances of finding a true biological effect in the tested interventions. Future researchers should think carefully about the nature of placebos that are used in such studies.

The clinical data is not sufficiently strong to warrant a large trial in this area yet, although it is an area worth following up. As for the other dietary supplements, we are unconvinced that there is sufficient biological or clinical data to suggest that further clinical trials are needed, although we would be happy to revise such a statement in the future if a new and convincing critical mass of evidence emerges.

Future studies should use outcome measures that are more readily clinically interpretable and should be informed by the outcome of the Harmonizing Outcomes for Eczema (HOME) project (Schmitt 2010; Schmitt 2011).

The measurement of surface area involvement is just one example of lack of consistency that could be addressed by harmonisation of outcome measures. Some have used terms such as 'eczema extent', 'eczema extension', 'area affected', and 'affected areas' in unclear ways; and it is equally unclear how and whether extent should be combined with other signs of eczema, such as oedema, redness, and scaliness.

Because little is known about how these supplements could work at a biologic level in allergic disease, little is known about their duration of action. This means that they are probably unsuitable for testing in cross‐over designs where each participant is given both treatments to try, because the effect of taking the first treatment may hang over into the next treatment phase.

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