Phenylthiocarbamide taste perception and susceptibility to motion sickness: linking higher susceptibility with higher phenylthiocarbamide taste acuity.

OBJECTIVE: This study is the first attempt to link quantified phenylthiocarbamide bitter taste recognition threshold with susceptibility to motion sickness.

SUBJECTS: The study was conducted on a sample of 291 teenage Rajput children (146 males and 145 females; age range 13-19 years) from the Sirmour district of Himachal Pradesh, India. Phenylthiocarbamide taste sensitivity was measured by administering a serial dilution of a freshly prepared phenylthiocarbamide solution, following the method of Harris and Kalmus. Motion sickness susceptibility was assessed retrospectively via interview.

RESULTS: About 40 per cent of the subjects had experienced motion sickness in the past. The mean and standard deviation of phenylthiocarbamide taste thresholds in non-tasters and tasters were 0.83 +/- 0.87 and 7.98 +/- 1.86, respectively. A bimodal distribution test (D/S) index of 5.24 confirmed bimodality of phenylthiocarbamide taste threshold distribution. The Mann-Whitney U test rejected the null hypothesis of mu 1 = mu 2 and thus confirmed the existence of differences in the distributions of phenylthiocarbamide taste threshold between individuals susceptible and not susceptible to motion sickness. Individuals susceptible to motion sickness had lower mean and median taste thresholds, indicating higher phenylthiocarbamide taste sensitivity, compared with non-susceptible individuals. The frequency of non-tasters was about 10 per cent in both motion sickness susceptible and non-susceptible individuals. The simple division of phenylthiocarbamide tasting ability into tasters and non-tasters was a less sensitive criterion with which to measure the association of this ability with motion sickness susceptibility. However, further differentiation of tasters into weak threshold, medium threshold and super threshold ('supersensitive') tasters clearly revealed a highly significantly increased risk of motion sickness in super threshold tasters (i.e. threshold solution number >or=12). The ratio of motion sickness susceptible individuals to non-susceptible individuals was 1:1.7 for non-tasters (threshold solution numbers zero to three) and weak and medium tasters (threshold solution numbers four to 11), but the trend was reversed for super threshold tasters (threshold solution numbers 12 and 13), in whom the ratio was 2:1.

CONCLUSION: Individuals exhibiting greater phenylthiocarbamide taste acuity (i.e. supersensitive tasters) had a higher susceptibility to motion sickness than did non-, weak and medium phenylthiocarbamide tasters, as measured in terms of their taste thresholds (i.e. threshold solution numbers zero to 11).