Wednesday December 10 2008
Hot drinks may have a placebo effect that eases cold and flu symptoms
An old wives’ tale remedy of taking hot fruit drinks "really does ease your sniffles", according to The Daily Mail. The newspaper says that researchers have found that symptoms of colds and flu can be relieved by drinking hot fruit cordial.
The research behind the stories had 30 volunteers with cold symptoms drink heated or room temperature blackcurrant cordial. Scientists measured volunteers’ nasal breathing and asked them how the drink changed their symptoms.
This small pilot study was carefully conducted but has numerous limitations, and the findings have been overinflated by the news. Hot drinks did not improve breathing, only the volunteers’ reported symptoms.
The participants knew what they were drinking, so the hot drink could have had a placebo effect, with people expecting to feel better from having something warm. In addition, the study did not directly comparethe hot and cold cordials to each other, other drinks or existing cold remedies.
Taking plenty of fluids is important when dealing with colds and flu, and these may be hot or cold. People with a cold should follow their preference for whichever they find more soothing.
Where did the story come from?
This research was conducted by Prof R. Eccles and Dr A. Sanu of the Common Cold Centre at Cardiff University, Wales. No sources of funding were reported by the study. It was published in the peer-reviewed medical journal Rhinology.
What kind of scientific study was this?
This was a randomised controlled trial investigating the effects of a hot or cold drink on upper airway symptoms of cold and flu such as cough, runny nose, and conductance of air through the nasal mucosa (the mucous membrane lining the nasal cavity).
Staff and students from Cardiff University were recruited into the study using advertisements. To participate in the study they had to be at least 18 years old and have cold or flu symptoms that had lasted at least a week.
Participants also needed to have at least two symptoms of moderate severity, based on a four point scale (absent, mild, moderate and severe). People were excluded if they had taken any cold remedies or medication that might ease symptoms or if they had ingested hot food or drink in the past hour.
Before the start of the study, participants gave a subjective assessment of their current symptoms using a visual analogue sliding scale, e.g. zero being an extremely clear nose, to 100, which is an extremely blocked nose. Nasal resistance to airflow was measured with rhinomanometry, where participants breathed into a facemask with their lips sealed around a pressure sensing tube.
Subjects were randomly allocated either a hot or room-temperature drink of apple and blackcurrant cordial that was drunk within 10 minutes of their rhinomanometry test. Subjective symptoms and nasal resistance tests were repeated immediately, then again 15 and 30 minutes later.
The primary outcome measured was change in conductance of airflow, while secondary outcomes were changes in subjective cold symptoms.
What were the results of the study?
There were 15 subjects in each of the two drink groups. Subjects were on average 20.8 years of age and 70% were female while 30% were male.
Testing for objective measures found conductance of nasal airflow was not effected by the hot drink at any time. However, the room-temperature drink caused a significant reduction in airflow conductance at 15 and 30 minutes.
In subjective measures, the hot drink caused an immediate significant improvement in the sensation of airflow (i.e. the nose felt clearer), which was sustained at 15 and 30 minutes.
The hot drink caused immediate improvement in sensation of cough, sore throat and chills, and these symptoms remained significantly reduced at 15 and 30 minutes. Tiredness was also significantly improved immediately, but at 30 minutes this improvement was no longer significant.
The hot drink did not have immediate effect on runny nose and sneezing, but these became significantly reduced 15 and 30 minutes later.
Conversely, the room temperature drink caused an immediate and sustained reduction in sneezing, and significantly reducing cough and runny nose symptoms at 15 and 30 minutes. It had no effect on sore throat, chills or tiredness at any time.
What interpretations did the researchers draw from these results?
The authors conclude that hot drinks do not have any effect upon nasal conductance but do provide some subjective reduction in most cold symptoms.
What does the NHS Knowledge Service make of this study?
This small pilot study was carefully conducted, but it has numerous limitations and the findings have been overinflated by the news. Points to note about this study:
- There appeared to be no direct statistical comparisons between the hot and room temperature drinks for any of the outcomes that were assessed. Therefore it is not possible to say from this study whether hot and room temperature drinks differ in their effects.
- The sample size was very small, which reduces the reliability of findings, as it is less certain any differences were not simply due to chance.
- The only objective outcome measured was airflow conductance, which was not significantly affected by hot drinks (although there was a significant reduction in conductance with the room temperature drink).
- Although there was an increased number of subjective symptoms that improved with the hot drink compared to the cooler drink, these should be interpreted with caution because the study could not be blinded. This may have led to the placebo effect of people drinking a hot drink expecting it to make them feel better.
- The news reports all highlight that it is warmed fruit cordial that is best for colds. However, this research has looked only at hot or cool apple and blackcurrant cordial; without testing, this fruit cordial cannot be assumed to be any better than any other hot or cold drink, e.g. water, tea or coffee.
- It is also unclear whether it has to be a drink or whether the same effect would be seen from hot or cold foods, or even whether anything has to be consumed at all and it is just a question of keeping the body warmer, which could also be achieved through warm clothes.
- This was an otherwise young and healthy student population; research would be needed among other populations before generalising these results.
For now it makes sense that people with cold and flu symptoms take rest, avoid strenuous activity and drink plenty of fluids. These fluids can be hot or cold, depending on preference and what an individual finds most relieving.
Sir Muir Gray adds...
Yet again my mother is proved right.