Author (s), year Test method Statistical analysis Zinc level at baseline Zinc status after treatment/intervention group Zinc status after treatment/placebo group Significant improvement against placebo Taste status/intervention group Taste status/placebo group Significant improvement against placebo Ikeda et al., 2013 [23 ] Filter paper disc method Wilcoxon rank-sum test and Fisher’s exact test 71.1 µ g/dl zinc group, 73.5 µ g/dl placebo group NR NR NR NR NR NR Sakagami et al., 2009 [24 ] Filter paper disc method and serum zinc level Shirley-Williams test and unpaired student’s t -test, Dunnett’s test, Fisher’s exact test ↓ 69 µ g/dl Serum zinc level ↑ 5.7 ± 13.5 (17 mg), 11.4 ± 16.6 (34 mg), and 20.6 ± 21.3 (68 mg), respectively, ( 1.8 ± 12.7 ( The efficient rate of gustatory sensitivity was 51.9%, 80.0% and 89.3% in the 17 mg, 34 mg and 68 mg zinc-treated groups, respectively The efficient rate (63.0%) Stewart-Knox et al., 2008 [25 ] Detection thresholds for sweet, sour, salty, bitter and umami Factorial ANOVA Within normal range for placebo and zinc groups (11–18 µ ·mol/l) Zinc level increased postintervention in both groups and greater in the 30 mg group 13.05 ± 1.66 µ ·mol/l Acuity for salt taste was greater in the 30 mg supplemented group (0·84 409 (SD 0·13 349) 15 and 30 mg Zn did not improve any tastes acuity 0·75 045 ± 0·210 Heckmann et al., 2005 [26 ] Filter paper strips and serum zinc level T -test for independent samples and correlation (Pearson’s) test72.78 ± 18.38 mg/dl No significant change in serum zinc level before and after treatments. 81.53 ± 19.61 72.01 ± 10.22 There were significant improvements in the zinc group compared to the placebo group 25.7 ± 6.5 21.2 ± 5.7 Matson et al., 2003 [27 ] Filter paper disc method, questionnaire and serum zinc level Unpaired t -test Placebo 10.9 ± 1.1_ µ ·mol/l Intervention 9.9 ± 1.6 µ ·mol/l Intervention 10.4 ± 1.4 µ ·mol/l Placebo 10.5 ± 1.6 µ ·mol/l NS Not improved Not improved NS Sakai et al., 2002 [28 ] A questionnaire, filter paper disc method and serum zinc level Student’s t -test and Wilcoxon’s test For zinc-deficient group ≤69 µ g/dl, idiopathic (70 µ g/dl ≥ Significantly greater increase in serum zinc level after treatment 81.6 µ g/dl Serum zinc level after treatment 72.3 µ g/dl There was a significant difference between groups in objective improvements in taste 28 patients improved and 9 not improved 16 improved and 20 not improved Yoshida et al., 1991 [29 ] Filter paper disc method and serum zinc level Chi-square test For zinc-deficient group, 60–69 µ g/dl; for idiopathic group, 70 µ g/dl or higher Serum zinc concentration was significantly higher during the intervention period, 94.0 ± 24.6 (n = 20) 71.9 ± 10.9 (n = 23) A significant difference was detected between the two groups in therapeutic efficiency (23 patients improved and 5 unchanged) 13 patients improved and 11 unchanged Mahajan et al., 1982 [30 ] The threshold of taste detection and recognition for salty, sweet and bitter, and serum zinc level Paired student’s t -test Intervention 81 ± 8 µ g/dlµ g/dl 110 ± 14 µ g/dl 84 ± 9 µ g/dl Improved Not improved Mahajan et al., 1980 [31 ] The threshold of taste detection and recognition for salty, sweet and bitter, and serum zinc level Independent student’s t -test for unpaired data Serum zinc level in treatment group 70 µ g/dl, lower than the control group The mean plasma zinc level increased significantly from 75 ± 8 to 97 ± 10 µ g/dl No change (75 ± 15 to 80 ± 15) Significant improvement in sweet, salty, and bitter taste Not improved Mahajan et al., 1979 [32 ] The threshold of taste detection and recognition for salty, sweet and bitter, and serum zinc level Independent student’s t -test for unpaired data 75.0 ± 2.0 µ g/dl zinc group 97.2 ± 3.2 µ g/dl zinc group NR Sig Improved Not improved Atkin-Thor et al., 1978 [33 ] The threshold of taste detection and recognition for salty, sweet and bitter, and zinc concentration in hair NR Zinc concentration in hair before treatment is 2 (10%) where the normal range 180 ± 4 ppm (100%) The serum zinc level was not published in the study; however, zinc concentration in hair increased in 85% of patients NR Significant improvement in taste acuity in the supplemented group by 95% of patients 6 weeks after treatment NR Henkin et al., 1976 [34 ] The threshold of taste detection and recognition for salty, sweet and bitter measured with the total concentration of zinc and copper and a questionnaire of taste acuity Student’s t -test NR NR NR NR Significant improvement in taste disorder at 3 months NR NR
