Najafizade et al. Preventive effects of zinc sulfate on taste alterations in patients under irradiation for head and neck cancers: A randomized placebo-controlled trial. J Res Med Sci. 2013; 18(2):123-126.
In this RCT, zinc sulfate 50 mg three times daily vs placebo was evaluated in 35 adult patients with head and neck cancers receiving radiotherapy (RT), with or without chemotherapy. Zinc therapy began with RT and continued for 1 month. Significant increases in taste perception threshold for bitter, salty, sweet, and sour tastes occurred in the placebo group (p=.001) after RT and 1 month later. There was only a slight increase in taste perception threshold for salty taste (p=.046) in those who received zinc, without any relevant side-effects. This small study showed that zinc supplementation prevented radiation-induced taste alterations, but confirmatory studies are needed, especially given the negative results of a larger, more robust trial (see next study).
Halyard et al. Does zinc sulfate prevent therapy-induced taste alterations in head and neck cancer patients? Results of phase III double-blind, placebo-controlled trial from the North Central Cancer Treatment Group (N01C4). Int J Radiat Oncol Biol Phys. 2007; 67(5), 1318-1322.
This multi-institutional double-blind RCT evaluated the effects of zinc sulfate on taste alteration in head and neck cancer patients undergoing radiotherapy (RT). A total of 169 evaluable patients were randomized to oral zinc sulfate 45 mg three times daily (intervention, n=84) vs placebo (n=85), given throughout RT and for 1 month after. The dosage chosen had previously been used in a small 1998 pilot study by Ripamonti et al (40) that generated positive results. Weekly assessments were made during RT and at 1, 2, 3, and 6 months after RT completion. Parameters to evaluate the efficacy included patient-reported taste alterations using a previously validated questionnaire, a general quality-of-life questionnaire that used a linear analog assessment scale, and physician-reported patient weight. Patients requiring RT cessation because of radiation-induced toxicity were also tracked. Interval to first taste alteration was the primary endpoint. Although zinc sulfate as prescribed was well tolerated, it did not significantly increase the interval to taste alterations, nor did it decrease the incidence of taste alterations or intervals to taste recovery. The larger study population and more robust trial design likely accounts for the divergent results compared with other trials.
Coles CL, et al. Infectious etiology modifies the treatment effect of zinc in severe pneumonia. Am J Clin Nutr. 2007;86(2):39.
This double-blind RCT of 299 children aged 2 to 23 months who were hospitalized for severe pneumonia evaluated whether bacterial vs nonbacterial etiology, as determined by C-reactive protein (CRP) levels, altered the efficacy of adjuvant zinc therapy. In those with suspected bacterial pneumonia, the zinc-treated group required an additional 20 hours to recover, resulting in a longer hospital stay compared with the placebo group. No difference in recovery time was detected in patients with nonbacterial pneumonia, suggesting that adjuvant zinc therapy for patients with bacterial pneumonia may increase recovery time and length of hospital stay. However, because the etiology of pneumonia was determined by CRP concentration, it is possible that some subjects were misclassified.
Lin LC, et al. Effects of zinc supplementation on clinical outcomes in patients receiving radiotherapy for head and neck cancers: a double-blinded randomized study. Int J Radiat Oncol Biol Phys. 2008;70(2):368-373.
One hundred subjects with cancers of the head and neck undergoing radiotherapy or chemoradiotherapy participated in this study to determine if zinc supplementation (25 mg Pro-Z, 3 times daily) could affect survival, including overall survival, disease-free survival, local-free survival, and metastasis-free survival. Three-year local-free survival was minimally affected by zinc supplementation compared with placebo. However, in patients with Stage III-IV disease who simultaneously received chemoradiotherapy, zinc supplementation significantly enhanced 3-year local-free survival possibly due to decreased radiotherapy-induced mucositis and dermatitis, resulting in less interruption of the chemoradiotherapy regimen. Additional studies with more participants and longer follow-up periods are necessary.
Kelishadi R, et al. Effect of zinc supplementation on markers of insulin resistance, oxidative stress, and inflammation among prepubescent children with metabolic syndrome. Metab Syndr Relat Disord. 2010;8(6):505-510.
This triple-blinded, randomized, crossover trial evaluated the effect of zinc supplementation on markers of metabolic syndrome in 60 obese children. Participants were randomized to receive either elemental zinc 20 mg/day or placebo for 8 weeks (n=30 each group). After a 4-week washout period, the groups crossed over. Blood pressure, fasting plasma glucose, lipid profile, insulin, apolipoproteins A-1 and B, high sensitivity C-reactive protein (hs-CRP), leptin, oxidized low-density lipoprotein, and malondialdehyde levels were measured during all study phases. After receiving zinc, a significant decrease in ApoB/ApoA-1 ratio, ox-LDL, leptin, malondialdehyde, total and LDL-cholesterol levels was documented (p<.05), whereas no significant change in these parameters was detected in the placebo group. Levels of hs-CRP, markers of insulin resistance, mean weight, BMI, and BMI Z-score also decreased significantly after receiving zinc (p<.05), whereas these values increased after receiving placebo. The authors suggest that the effect of zinc supplementation on childhood obesity should be further investigated.