The sense of taste is essential to the health and psychological well-being of an individual. Taste disorders can range from lack of taste, to distortion of taste, to reduced ability to taste. Any disorder in taste perception can lead to conditions like malnutrition and consumption of poisonous food substances. The cause may be due to disease, drugs, radiation treatment, or ageing; or it may result from unknown causes. Various treatment methods have been used to improve taste sensation. These include the use of zinc compounds, pilocarpine, alpha lipoic acid, transcranial magnetic stimulation, ginkgo biloba and acupuncture.
What was the research?
A systematic review to examine the best method for the management of zinc-deficient/idiopathic (of unknown cause) taste disorders and taste disorders secondary to chronic renal failure in children and adults.
Who conducted the research?
The research was conducted by a team led by Sumanth Kumbargere Nagraj of Melaka-Manipal Medical College, Malaysia, on behalf of Cochrane Oral Health. Renjith P George, Naresh Shetty, David Levenson, Debra M Ferraiolo and Ashish Shrestha were also on the team.
What evidence was included in the review?
We collected and analysed all relevant studies to answer this question and found 10 randomised controlled trials in which a total of 581 subjects received different treatments. Nine trials assessed the benefits of zinc compounds and one trial assessed the effects of acupuncture. We only included studies on taste disorders in this review that were either idiopathic, or resulting from zinc deficiency or chronic renal failure.
Two trials were from Germany, three from Japan, two from the UK, and three from the US. These studies compared zinc with placebo or acupuncture with sham procedure for patients with taste disorders. Two were government funded, three were privately funded, two were funded by a pharmaceutical company and three trials did not mention funding details.
What did the evidence say?
When patients with taste disorders are given zinc, compared to placebo:
– we found very low-quality evidence that was insufficient to conclude on the role of zinc supplements to improve taste acuity reported by patients and very low-quality evidence that zinc supplements improve taste acuity in patients with zinc deficiency/idiopathic taste disorders;
– zinc supplementation showed adverse events like eczema, nausea, abdominal pain, diarrhoea, constipation, decrease in blood iron, increase in blood alkaline phosphatase and minor increase in blood triglycerides;
– no studies were found that looked at improvement in taste discrimination or quality of life.
When patients with taste disorders are given acupuncture, compared to sham procedure:
– we found very low-quality evidence that is not sufficient to conclude on the role of acupuncture for improving taste discrimination in cases of idiopathic dysgeusia (distortion of taste) and hypogeusia (reduced ability to taste);
– acupuncture trial did not show adverse events;
– no studies were found that looked at improvement in taste acuity or quality of life.
We were unable to draw any conclusions regarding the superiority of zinc supplements or acupuncture as none of the trials compared these interventions.
How good was the evidence?
The evidence was of very low quality, due to issues with the design and reporting of the included trials.
What are the implications for dentists and the general public?
Giving zinc supplements or acupuncture may have some benefit in treating taste disorders. However, we still need more high-quality studies to ascertain the role of zinc supplements and acupuncture in treating taste disorders.
What should researchers look at in the future?
Further research should be undertaken in the management of taste disorders by conducting well planned randomised controlled trials (RCTs) with more clarity and uniformity in the variables.
Kumbargere Nagraj S, George RP, Shetty N, Levenson D, Ferraiolo DM, Shrestha A. Interventions for managing taste disturbances. Cochrane Database of Systematic Reviews 2017, Issue 12. Art. No.: CD010470. DOI: 10.1002/14651858.CD010470.pub3.
This post is an extended version of the review’s plain language summary, compiled by Anne Littlewood at the Cochrane Oral Health Editorial Base.