Impact of daily preventive zinc or therapeutic zinc supplementation for diarrhea on plasma biomarkers of environmental enteric dysfunction among rural Laotian children: a randomized controlled trial

Authors: WESSELLS, RYAN - University Of California, Davis; HINNOUHO, GUY-MARION - University Of California, Davis; BARFFOUR, MAXWELL - University Of California, Davis; ARNOLD, CHARLES - University Of California, Davis; KOUNNAVONG, SENGCHANH - Khon Kaen University; KEWCHAROENWONG, CHIDCHAMAI - Khon Kaen University; LERTMEMONGKOLCHAI, GANJANA - Khon Kaen University; SCHUSTER, GERTRUD - University Of California, Davis; Stephensen, Charles; HESS, SONJA - University Of California, Davis

Submitted to: American Journal of Tropical Medicine and Hygiene
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/11/2019
Publication Date: 2/5/2020
Citation: Wessells, R.K., Hinnouho, G., Barffour, M., Arnold, C., Kounnavong, S., Kewcharoenwong, C., Lertmemongkolchai, G., Schuster, G., Stephensen, C.B., Hess, S. 2020. Impact of daily preventive zinc or therapeutic zinc supplementation for diarrhea on plasma biomarkers of environmental enteric dysfunction among rural laotian children: a randomized controlled trial. American Journal of Tropical Medicine and Hygiene. 102(2):415-426. https://doi.org/10.4269/ajtmh.19-0584.
DOI: https://doi.org/10.4269/ajtmh.19-0584

Interpretive Summary: Children living in areas of the world where environmental sanitation is poor, such as rural areas of Laos where this study was conducted, may suffer from decreased linear growth (i.e., stunting) due to a condition known as environmental enteric dysfunction (EED). The essential nutrient zinc is often deficient in the diets of children in such settings. Zinc deficiency can impair immune function and increase the risk of enteric infections, such as infectious diarrhea. The objective of this study was to investigate the effect of different forms of zinc supplementation on plasma markers of intestinal health and inflammation that would be altered by EED and might be improved by zinc supplementation. Plasma citrulline was chosen as the marker of intestinal health while the ratio of kynurenine-to-tryptophan concentrations (KT ratio) was used as a marker of inflammation. The KT ratio is elevated during inflammation because the amino acid tryptophan is reduced in plasma as it is metabolized to kynurenine, a mediator of immune function. In a double-blind randomized controlled trial, 3407 children aged 6-23 months of age were randomized into one of four groups and followed for 36 weeks. The four groups were daily preventive zinc dispersible tablet (7 mg zinc; PZ), daily multiple micronutrient powder (10 mg zinc, 6 mg iron and 13 other micronutrients; MNP), therapeutic zinc supplements for the treatment of diarrhea (20 mg/d for 10 days with each diarrhea episode; TZ), or daily placebo powder (Control). The mean age at enrollment was 16 m, 37% of children were stunted and 83% were zinc deficient. At baseline, mean plasma citrulline, kynurenine and tryptophan concentrations were 24.6, 3.27 and 72.3 µmol/L, respectively; the mean KT ratio was 45.9. Values at the end of the study were similar and means did not differ among the four treatment groups. Thus the zinc interventions had no significant effect on these markers of intestinal health and inflammation, even though there was a high prevalence of stunting and zinc deficiency in this population. This unexpected result highlights a need to better understand the etiology of EED in such settings so appropriate preventive measures can be developed.

Technical Abstract: Environmental enteric dysfunction (EED) may be ameliorated by zinc supplementation. The objective of this study was to investigate the impact of different forms of zinc supplementation on biomarkers of EED (i.e. plasma citrulline, kynurenine, and tryptophan concentrations and the kynurenine:tryptophan (KT) ratio) among young Lao children. In a double-blind randomized controlled trial, 3407 children aged 6-23 mo were randomized into one of four groups and followed for ~36 weeks: daily preventive zinc dispersible tablet (7 mg zinc; PZ), daily multiple micronutrient powder (10 mg zinc, 6 mg iron and 13 other micronutrients; MNP), therapeutic zinc supplements for diarrhea treatment (20 mg/d for 10 days; TZ), or daily placebo powder.Plasma samples at baseline and endline for 359 children were analyzed for citrulline, kynurenine, and tryptophan concentrations. At baseline, the prevalence of stunting and zinc deficiency were 37% and 83%, respectively. Mean plasma citrulline, kynurenine, and tryptophan concentrations were 24.6 + 5.4 µmol/L, 3.27 + 0.83 µmol/L, and 72.3 + 12.9 µmol/L, respectively; the mean KT ratio (*1000) was 45.9 + 12.0. At endline, neither plasma citrulline, kynurenine, nor tryptophan concentrations, nor the KT ratio, differed among intervention groups (P > 0.05). In this population, PZ, MNP, and TZ had no overall effect on plasma concentrations of citrulline, kynurenine, and tryptophan, or the KT ratio. The need remains to better understand the etiology of EED, and the development of biomarkers to diagnose EED and evaluate the impact of interventions.