Passion fruit peel ‘relief’ for asthmatics

Behind the Headlines

Thursday May 15 2008

“Passion fruit peel can  ‘significantly’ improve the symptoms of asthma,” the Daily Mirror reported today. The newspaper said that scientists tested the peel on asthmatics and found that 90% of them were cured of breathlessness and wheezing was cut in about 80% of them after four weeks.

The Daily Express also covered the story and said that patients given an extract from the fruit’s peel had reduced wheezing, coughing and shortness of breath. It reported that this may be due to the fruit’s “anti-oxidant, anti-allergic and anti-inflammatory properties”.

Although this study did find that the people who took the purple passion fruit peel (PFP) reported less asthma symptoms than those who took a placebo, the study group was of a small size with only 43 asthmatics, and it had several limitations. In addition, the objective measure of asthma that was used, FEV1, actually showed a significant improvement in the placebo group after four weeks, but not in the group that took the PFP.

The fact that nearly all the participants were experiencing symptoms of wheeze, cough and breathlessness at the beginning of the study, and that the prevalence of all these symptoms had declined so much in both groups after four weeks, brings into question the methods used to define asthmatic symptoms.

More trials will be needed to see whether there are real asthma benefits from tablets of passion fruit peel, that they persist in the long term (the trial was only four weeks), and to ensure that there are no adverse effects from the tablets.

Where did the story come from?

The research was carried out by Ronald Ross Watson and colleagues from the Southwest Scientific Editing and Consulting L.L.C. and the Mel and Enid Zuckerman Arizona College of Public Health, Tucson, US, the Mashhad University of Medical Sciences, Iran, and the Gracefield Research Centre, New Zealand.

The study was funded by Southwest Scientific Editing and Consulting and Mashhad University. The study was published in the peer-reviewed medical journal: Nutrition Research.

What kind of scientific study was this?

In this randomised controlled trial the researchers aimed to investigate the effects of purple passion fruit peel (PFP) on asthma symptoms. PFP contains a unique mixture of bioflavonoids, natural pigments in fruit and vegetables, that reportedly have antioxidant properties and many health benefits. It is believed that PFP could be of benefit to asthmatics in particular by decreasing the body’s production of nitric oxide. This chemical is involved in the processes of airway responsiveness and inflammation when a person is exposed to certain stimuli.

The researchers enrolled 43 asthmatics between the ages of 18 and 60. At their enrolment visit, all the participants had a full medical and physical examination, including blood tests, skin prick allergy testing and spirometry, to test their lung function.

To be eligible for inclusion they had to have a forced expiratory volume (FEV1), the volume of air that can be forcibly exhaled in the first second after breathing in as much as possible, of between 30 and 75% of the predicted normal for their age, sex and height. In addition, this had to improve by more than 15% after treatment with an inhaled bronchodilator.

The researchers had excluded anyone with chronic obstructive airways disease; heart, liver, kidney, or hormonal disease; those pregnant, breastfeeding or taking the oral contraceptive pill; and smokers or those drinking any alcohol. The study participants were allowed to take their normal medications with the exception of those that can aggravate asthma symptoms, such as aspirin.

On their second visit, the participants’ lung function was retested and they were randomly allocated to receiving either a pill containing the dark red powdered extract of South African PFP (22 people) or an identical inactive placebo pill (21 people). The participants took the tablets every day for four weeks and also attended a weekly clinic to check for side effects. At four weeks, their asthma symptoms and spirometry tests were assessed again and they were asked to hand in any remaining tablets so that the researchers could see how compliant they had been in taking them.

Throughout the four-week trial period, the participants and researchers were unaware who was taking the active or placebo pills.

What were the results of the study?

The average age of the participants in each group was 36, and there were no differences in the symptoms or severity of asthma between the groups. Of the 43 study participants, 98% completed the study, with only one participant in the PFP group dropping out.

At the start of the study, all the participants reported wheeze. After the four-week trial, significantly fewer people in the PFP group reported wheeze (19.1%) compared to those who received placebo (78.9%).

Likewise, cough declined significantly for the PFP group from 95.2% at the beginning of the study to 23.8% after four weeks. In comparison, the participants with cough in the control group declined from 100% to 52.6%.

The prevalence of breathlessness reduced significantly from 90% to 10% in the PFP group compared to a reduction from 78.9% down to 36.8% in the placebo group. The forced vital capacity (FVC) the lung volume after breathing in as much as possible, increased significantly by the end of the study in the PFP group but not in the placebo group. The difference between these measurements is not reported. However, FEV1 was reported as being improved significantly in the placebo group, but not in the PFP group.

What interpretations did the researchers draw from these results?

The researchers conclude that their study “provides evidence that oral administration of PFP extract produced statistically significant improvement in the symptoms of asthma after only four weeks of supplementation”. They say that PFP could potentially supplement or partially replace standard antiasthmatic drugs.

What does the NHS Knowledge Service make of this study?

This study appears to show that extract of PFP taken in a tablet form may be of some benefit in improving asthma symptoms. However, there are a few important points to note:

  • This evidence comes from only one small trial. The small number of participants means that the numbers in each group may have been too small to detect the real size of the difference between taking PFP or placebo. Further larger trials are needed to confirm and strengthen confidence in these findings.
  • The duration of the trial and follow up was limited to only four weeks. It is not possible to tell whether any benefits would be sustained in the longer term (i.e. if the same benefits continue to be seen if the participants carry on taking PFP, or if symptoms return to their previous level when the participants stop taking PFP). Four weeks is also not a long enough period to determine if there any longer term adverse effects.
  • What was actually meant by the presence of wheeze, cough or breathlessness is unclear from the study report (i.e. whether that meant the symptoms were present only at the time of the examination, or present on that day, or over the past week etc). A more explicit measure of how frequently symptoms were occurring would have been beneficial for interpreting the true meaning of these results.
  • The fact that nearly all the participants were experiencing symptoms of wheeze, cough and breathlessness at the beginning of the study, and that the prevalence of all these symptoms had declined in both groups after four weeks, brings into question the meaning of these symptoms. For example, it is possible that on the first day of the study, particularly cold weather aggravated asthma symptoms, and by the end of the study the weather had improved. This could potentially explain some of the general improvement. Alternatively, the participants could have been comparing their lifetimes experience of their symptoms to the symptoms experienced from the four weeks of the study.
  • As the participants in both groups all reported less symptoms at the end of four weeks, it is not possible to say whether  their symptom reports were affected by the fact that they were all taking part in a study that measures symptoms of asthma (i.e. they may all have been expecting to improve).
  • Although all symptoms significantly improved in the PFP group, FEV1, which is a reliable indicator of lung function and severity of asthma, actually showed more improvement in the placebo group. However, although there were differences within the groups, it is not clear whether the objective measurements (i.e. spirometry results rather than patients’ subjective report of symptoms) actually differed statistically between the treatment and placebo groups.
  • There have been no demonstrated benefits from eating passion fruit pulp for asthmatics. The peel of the fruit would not normally be eaten and in this case was consumed in its powdered form in a tablet that is currently not available.

Sir Muir Gray adds…

One swallow does not make a summer. Let's see what a systematic review of all the research says.

Links to the headlines

The passion fruit ‘cure’ for asthma. Daily Express, May 15 2008

Asthma 'cure' in passion fruit peel. Daily Mirror, May 15 2008

Links to the science

Ross Watson R, Zibadi S, Rafatpanah H, et al. Oral administration of the purple passion  fruit peel extract reduces wheeze and cough and improves shortness of breath in adults with asthma. Nutr Res 2008; 28:166-171

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Edited by NHS Choices