Basis for changes in the global burden of disease estimates related to vitamin A and zinc deficiencies in the GBD 2017 and 2019 studies

Abstract Background: The Global Burden of Disease (GBD) Study provides estimates of death and disability from 87 risk factors, including some micronutrient deficiencies. Objectives: To review methodological changes that led to large differences in the disease burden estimates for vitamin A and zinc deficiencies between the GBD 2017 and 2019 Studies. Methods: GBD publications were reviewed; additional information was provided by GBD researchers. Results: Vitamin A deficiency prevalence is based on plasma retinol concentration, whereas the estimate for zinc deficiency prevalence uses dietary adequacy as a proxy. The estimated global prevalence of vitamin A deficiency for children aged 1-4 years in the year 2017 decreased from 0.20 (95%CI 0.17-0.24) in GBD 2017 to 0.16 (95%CI 0.15-0.19) in GBD 2019, while the global prevalence of zinc deficiency did not change between the two studies (0.09 (95%CI 0.04-0.17) and 0.09 (95%CI 0.03-0.18)). New to 2019 was that meta-analyses were performed using Meta Regression – Bayesian, Regularized, Trimmed (MR-BRT), a method developed for GBD. Due to this and multiple other methodological changes the estimated number of deaths due to vitamin A deficiency dropped from 233,000 (179,000–294,000) to 24,000 (3,000–50,000) from GBD 2017 to 2019, and for zinc deficiency from 29,000 (1,000–77,000) to 2,800 (700–6,500), respectively. Conclusion: The changes in the estimated disease burdens due to vitamin A and zinc deficiencies in the GBD reports from 2017 to 2019 are due primarily to changes in the analytical methods employed, so may not represent true changes in disease burden. Additional effort is needed to validate these results.