The main question addressed by this review was: what is the best method for the management of taste disorders?
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.
The Cochrane Oral Health Group carried out this review of existing studies, which includes evidence current to 5 March 2014. The review includes nine trials in which a total of 566 subjects received different treatments. Eight trials assessed the benefits of zinc compounds and one trial assessed the effects of acupuncture. Seven trials were parallel and two trials were cross-over randomised controlled trials. We only included studies on taste disorders in this review that were either idiopathic, or resulting from zinc deficiency or chronic renal failure.
The evidence to use zinc supplements to treat zinc deficient/idiopathic taste disorder and taste disorder secondary to chronic renal failure was insufficient. The trial using acupuncture to treat idiopathic taste disorder showed some benefit for taste discrimination. However, the small number of patients included in the trial, did not allow one to conclude its efficacy.
This summary review showed that zinc supplements may have some benefit in treating taste disorder. However, further research is necessary to make an impact on treatment choice.
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 in four trials out of eight. No adverse events were reported in the acupuncture trial.
There is insufficient evidence to conclude that either zinc or acupuncture can improve the health-related quality of life in taste disorder patients.
Quality of evidence
The quality of evidence found in this review was of very low to moderate quality due to issues with the way in which some of the included studies were conducted.
We found very low quality evidence that was insufficient to conclude on the role of zinc supplements to improve taste perception by patients, however we found moderate quality evidence that zinc supplements improve overall taste improvement in patients with zinc deficiency/idiopathic taste disorders. We also found low quality evidence that zinc supplements improve taste acuity in zinc deficient/idiopathic taste disorders and very low quality evidence for taste recognition improvement in children with taste disorders secondary to chronic renal failure. We did not find any evidence to conclude the role of zinc supplements for improving taste discrimination, or any evidence addressing health-related quality of life due to taste disorders.
We found 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). We were unable to draw any conclusions regarding the superiority of zinc supplements or acupuncture as none of the trials compared these interventions.
The sense of taste is very much essential to the overall health of the individual. It is a necessary component to enjoying one’s food, which in turn provides nutrition to an individual. Any disturbance in taste perception can hamper the quality of life in such patients by influencing their appetite, body weight and psychological well-being. Taste disorders have been treated using different modalities of treatment and there is no consensus for the best intervention. Hence this Cochrane systematic review was undertaken.
To assess the effects of interventions for the management of patients with taste disturbances.
We searched the Cochrane Oral Health Group Trials Register (to 5 March 2014), the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library Issue 1, 2014), MEDLINE via OVID (1948 to 5 March 2014), EMBASE via OVID (1980 to 5 March 2014), CINAHL via EBSCO (1980 to 5 March 2014) and AMED via OVID (1985 to 5 March 2014). We also searched the relevant clinical trial registries and conference proceedings from the International Association of Dental Research/American Association of Dental Research (to 5 March 2014), Association for Research in Otolaryngology (to 5 March 2014), the US National Institutes of Health Trials Register (to 5 March 2014), metaRegister of Controlled Trials (mRCT) (to 5 March 2014), World Health Organization's International Clinical Trials Registry Platform (WHO ICTRP) (to 5 March 2014) and International Federation of Pharmaceutical Manufacturers and Associations (IFPMA) Clinical Trials Portal (to 5 March 2014).
We included all randomised controlled trials (RCTs) comparing any pharmacological agent with a control intervention or any non-pharmacological agent with a control intervention. We also included cross-over trials in the review.
Two authors independently, and in duplicate, assessed the quality of trials and extracted data. Wherever possible, we contacted study authors for additional information. We collected adverse events information from the trials.
We included nine trials (seven parallel and two cross-over RCTs) with 566 participants. We assessed three trials (33.3%) as having a low risk of bias, four trials (44.5%) at high risk of bias and two trials (22.2%) as having an unclear risk of bias. We only included studies on taste disorders in this review that were either idiopathic, or resulting from zinc deficiency or chronic renal failure.
Of these, eight trials with 529 people compared zinc supplements to placebo for patients with taste disorders. The participants in two trials were children and adolescents with respective mean ages of 10 and 11.2 years and the other six trials had adult participants. Out of these eight, two trials assessed the patient reported outcome for improvement in taste acuity using zinc supplements (RR 1.45, 95% CI 1.0 to 2.1; very low quality evidence). We included three trials in the meta-analysis for overall taste improvement (effect size 0.44, 95% CI 0.23 to 0.65; moderate quality evidence). Two other trials described the results as taste acuity improvement and we conducted subgroup analyses due to clinical heterogeneity. One trial described the results as taste recognition improvement for each taste sensation and we analysed this separately. We also analysed one cross-over trial separately using the first half of the results. None of the zinc trials tested taste discrimination. Only one trial tested taste discrimination using acupuncture (effect size 2.80, 95% CI -1.18 to 6.78; low quality evidence).
Out of the eight trials using zinc supplementation, four reported 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 adverse events were reported in the acupuncture trial.
None of the included trials could be included in the meta-analysis for health-related quality of life in taste disorder patients.