A Taste-intensity Visual Analog Scale: An Improved Zinc Taste-test Protocol.

The first use of a zinc sulfate taste test documented a case report of a 13-year-old, 37-kg female who was unable to taste a 0.1% solution of zinc sulfate.1 Although the patient in the case study could not taste the solution, both the authors and their families could taste it. After the patient was supplemented with zinc sulfate, her weight increased, and she could taste the solution. After the supplementation was stopped, her weight subsequently decreased, and she was again unable to taste the solution. Supplementation was reintroduced, weight increased to 44.5 kg, and the zinc taste test was strongly positive. Since that case study, zinc sulfate taste acuity has been correlated with levels of serum zinc throughout pregnancy2 and with sweat-mineral analysis3 as well as with postpartum levels of serum zinc and postpartum depression4; however, the aforementioned reports have been disparaged due to limitations in their protocols.5 In addition, zinc sulfate taste acuity has been positively correlated to levels of salivary carbonic anhydrase 6 and negatively correlated to frequency of illness.6 Bryce-Smith and Simpson1,7 were the first to propose a method of assessment of zinc sulfate taste acuity. The Bryce-Smith and Simpson zinc taste test (BS-ZTT) uses 5 to 10 mL of a 0.1% zinc sulfate solution. The solution is administered orally, and the reaction of the tested individual is graded on an ordinal scale of 1 to 4 according to the subject’s response to the solution. A score of 1 is given to individuals in which “no specific taste or other sensation is noticed, even after the solution has been kept in the mouth for about 10 seconds”; 2 when “no immediate taste is noted, but after a few seconds a slight taste variously described as ‘dry,’ ‘mineral,’ ‘furry,’ or (more rarely) ‘sweet’ develops”; 3 when “a definite though not strongly unpleasant taste is noted almost immediately, and tends to intensify with time”; and 4 when “a strong and unpleasant taste is noted immediately.”7 An abstract from Johnson et al8 later documented another test protocol using a 0.1% solution of zinc sulfate. Similar to the BS-ZTT scale, the scale by Johnson et al8 is ordinal and ranges from 1 to 4. However, the descriptions for each category are more condensed than those of the BS-ZTT protocol; specifically, 1 = negative, 2 = slight, 3 = strong, and 4 = powerful/unpleasant.8 In 1993, Garg et al2 chronicled another method of assessment of zinc sulfate taste. The method employs 2 mL of a 1% solution that is retained in the mouth for 10 seconds as opposed to the 5 to 10 mL of a 0.1% solution that is retained for an unspecified amount of time in the BS-ZTT protocol. Also, the Garg et al2 protocol does not account for physical signs, such as those reflected by the BS-ZTT category 4. In 2004, Eaton et al3 introduced yet another zinc sulfate taste test in which 5 mL of 0.1% zinc sulfate solution is added to 50 mL of water and held in the mouth for 10 seconds, done late at night. Participants grade themselves on a scale of 0 to 4 rather than 1 to 4, and 0 = no response. Verbal descriptions for the other grades include 1 = a dry, bitter, acid, or metallic taste, but occasionally sweet; 2 = awareness that the solution is not water but no clear immediate response; 3 = immediate development of a taste as in grade 1; and 4 = a very strong, unpleasant taste, provoking the desire to spit it out.3 All variations of the zinc sulfate taste test agree that different individuals can perceive zinc sulfate differently and, likewise, that one individual can perceive zinc sulfate differently with time. However, protocols for assessment of a zinc sulfate taste, although similar among studies, have noteworthy differences among them, thus confounding proper scientific vetting of zinc sulfate taste mensuration. To date, most reports using similar methods of zinc sulfate taste assessment have had conflicting results, have not been published in their entirety, or have had significant problems in the study’s design, including the absence of exclusion criteria.5