Plasma and Nail Zinc Concentrations, But Not Hair Zinc, Respond Positively to Two Different Forms of Preventive Zinc Supplementation in Young Laotian Children: a Randomized Controlled Trial.

Plasma zinc concentrations (PZC) have been shown to significantly increase during zinc supplementation. This study investigated the effects of daily preventive zinc supplementation on hair and nail zinc concentrations compared with a control group. In a randomized controlled trial, 6- to 23-month-old children (n = 3407) in Lao PDR were randomly assigned to one of four groups and followed for ~ 36 weeks: daily preventive zinc dispersible tablet (7 mg/d; PZ), daily micronutrient powder (10 mg zinc/d; MNP), therapeutic zinc supplements for diarrhea treatment (20 mg/d for 10 days; TZ), or daily placebo powder (Control). Plasma, hair, and nail zinc concentrations were assessed in a sub-sample of participants (n = 457) at baseline and endline. At baseline, 75% of children had low PZC (< 65 μg/dL). At endline, geometric mean (95% CI) PZC were greater in the PZ and MNP groups compared with the TZ and control groups (P < 0.01), but hair zinc concentrations did not differ among groups (P = 0.99). Nail zinc concentrations were marginally higher in the PZ (115.8 (111.6, 119.9) μg/g) and the MNP (117.8 (113.3, 122.3) μg/g) groups than in the TZ group (110.4 (106.0, 114.8) μg/g; P = 0.055) at endline. This study does not support the use of hair zinc as a biomarker of zinc exposure in young children. However, it provides some evidence that zinc concentrations in nails may respond to supplemental zinc interventions and supports the need for collecting additional data on this emerging biomarker.