"Is YOGURT the secret to easing hay fever? Probiotics can 'relieve sneezing and itchy eyes','' the Daily Mail reports. New research found initial, but not definitive, evidence that probiotics may offer some relief from this common allergic condition for some people.
Hay fever affects around one in five people, causing frequent sneezing, a runny nose and itchy eyes. It happens when an allergic irritant sets off an immune response in the mucosa of the nasal passages, causing an allergic reaction. Most often, people are sensitive to seasonal allergens such as pollen, hence the name hay fever. However, some people can get symptoms all year round (this is known as allergic rhinitis).
There has been a lot of interest in whether probiotics – "healthy" bacteria that live in the gut – can relieve symptoms.
This review identified 23 trials investigating the effect of probiotic supplements on allergic rhinitis. These studies were highly variable in terms of their study populations, the probiotics used, outcomes measured and, importantly, results. While most studies found some benefit for at least one outcome, others found no benefit at all.
The authors concluded that probiotics may have a beneficial effect when added to other allergic rhinitis treatments, but that higher-quality, larger studies with standardised measures of effects are still needed.
Where did the story come from?
The study was carried out by researchers from the University School of Medicine in Nashville, US. The study's funding is not mentioned. It was published in the peer-reviewed medical journal International Forum of Allergy and Rhinology.
Most of the UK media coverage reported the study’s headline results uncritically, suggesting that yoghurt could be a cure for hay fever symptoms. However, not all yoghurt is probiotic, and it is not clear whether the people in these studies were taking these probiotics in the form of yoghurt or capsules. The study was not specific to people with hay fever, as it included people with allergic rhinitis not associated with seasonal allergens. The study did not find an overall effect on standard symptom scores, and the study authors did not recommend probiotics as a standalone cure.
What kind of research was this?
This was a systematic review that has searched the literature to identify randomised controlled trials (as well as two randomised crossover studies) that investigated the effects of probiotics on allergic rhinitis. Hay fever is a type of allergic rhinitis that medical specialists refer to as "seasonal allergic rhinitis".
Where study designs and measured outcomes were similar enough, it pooled the results of these studies in meta-analysis. The review aimed to see whether probiotic supplements helped people with allergic rhinitis.
Systematic reviews of randomised controlled trials are usually a good source of reliable evidence to show whether a treatment is helpful. However, the review is only as good as the studies that have been carried out.
What did the research involve?
Researchers searched for randomised controlled trials that studied the effect of probiotics on allergic rhinitis, according to pre-defined specifications, and summarised the results of the studies that came up to their quality standards. They then did a meta-analysis, where they pooled the results of those studies that had used standardised clinical measures for allergic rhinitis treatment, to get an overall picture of treatment effect.
The researchers found 153 studies, 42 of which were relevant. They excluded 19 studies, mainly because they didn't give results using standardised clinical outcome measures. The remaining 23 studies were mostly double-blind randomised controlled trials, with two randomised crossover studies. These studies, which included 1,919 participants, were included in the review.
The outcomes measured included two measures of symptom control. These were the Rhinitis Quality of Life Questionnaire (RQLQ), which includes questions about how much symptoms affect people's daily activities, and the Rhinitis Total Symptom Score (RTSS). Some studies had also measured blood levels of immunoglobin E (IgE) – a naturally occurring antibody involved in allergic reactions.
Where possible, they pooled trial results for these different measures to get an overall picture of the effect of probiotics.
What were the basic results?
The review found that 17 of the 23 studies reported a significant improvement in at least one of the outcomes measured for people taking probiotics, while six studies showed no benefit from probiotics.
Results of the meta-analysis were mixed. The only measure that showed a clear beneficial effect from taking probiotics was the RQLQ. When the results were pooled from the four studies that measured RQLQ in a way that allowed direct comparison, the study found a mean reduction in score compared to placebo of -2.23 points (95% confidence interval (CI) -4.07 to -0.4). The researchers say a reduction of 0.5 or more is considered important.
The researchers found no statistically significant difference between placebo and probiotic treatment for the RTSS (pooled analysis of four trials) or IgE scores (from eight trials).
How did the researchers interpret the results?
The researchers were cautious about the results. They said that differences between the studies, such as different types of probiotic used and different sizes in the study populations, meant it was possible that the positive effect of probiotics on quality of life they found "may be at least partially due to confounding factors and differences between studies". They point out that the two older, smaller studies showed a bigger effect, while two bigger, more recent studies found no effect or a small effect.
They say their meta-analysis "suggests that probiotics have the potential to alter disease severity, symptoms and quality of life" for people with allergic rhinitis, but that the evidence is not strong enough to recommend using probiotics alone to relieve it.
This review has identified 23 trials investigating the effect of probiotics upon allergic rhinitis, which most people experience as hay fever. Overall, it found some evidence that taking probiotic yoghurts or supplements could improve the quality of life of people with allergic rhinitis, compared to taking placebo. However, it didn't find a direct effect on overall symptoms, or on levels of IgE in the blood.
The review of the data showed some of the problems with research into probiotics in relation to allergies. Many different strains of probiotic organisms were used in the study, although most were from the families Bifidobacterium or Lactobacillus. It's possible that some strains work well and others don't work at all. It’s also unclear from the review what form these probiotics were being taken in – for example, in the form of yoghurt or yoghurt drinks, or as capsules or tablets. This could affect absorption and effects.
The populations included in these studies are also likely to be highly variable. The age categories, for example, ranged from young children in some, to middle-aged adults in others. We also don’t know what they were specifically suffering from. For example, some could have had hay fever, while others could have had an allergy to dust mites or animal fur.
Only a few studies reported their results using standardised measures, making it hard to pool data from different studies. Though 23 studies were identified, pooled analyses for effects on symptoms and quality of life came from only four studies each.
The review showed that 17 of the 23 studies included found at least one positive clinical outcome for patients taking probiotics. However, this did not translate into convincing results on symptom scores when results from four of these studies were pooled. Pooled results on quality of life were positive, though without further information it is not possible to tell how much effect there may be on the person’s daily life. The researchers say that a reduction of 0.5 or more is considered important, so the 2.23 reduction in score should make a difference. However, if probiotics had no effect on rhinitis symptoms, it would be interesting to know in what ways they were helping a person’s quality of life.
Allergic rhinitis, or hay fever specifically, is a common problem in the UK, and treatments don't help everyone. While the evidence for probiotics is not strong enough to recommend them as treatment, the researchers said that few people reported any adverse effects from taking them. Some people taking probiotics reported diarrhoea, abdominal pain or flatulence (wind), but so did similar numbers of people taking placebos.
Overall, the review cannot answer with certainty how much benefit probiotics may have, and as the researchers say, better-quality evidence is needed.
Analysis by Bazian
Edited by NHS Website
Links to the headlines
Daily Mail, 7 May 2015
The Daily Telegraph, 6 May 2015
Daily Express, 6 May 2015
Links to the science
International Forum of Allergy & Rhinology. Published online April 20 2015