Serum Zinc Concentrations by Inflammation Status, Time of Day, and Fasting Status for Estimating Zinc Deficiency in 6-59-Mo-Old Children: Results from the Brazilian National Survey on Child Nutrition (ENANI-2019)

BACKGROUND

Serum zinc concentration (SZC) is considered the best biomarker of zinc status in population-level evaluations. However, zinc deficiency (ZD) estimations can be biased if they do not consider blood collection timing, inflammation, and fasting status.

OBJECTIVES

The objectives of this study were to determine SZC without and with adjustment for inflammation, according to blood collection timing and fasting status, estimate ZD prevalence, and evaluate the associated factors with ZD in a representative sample of Brazilian children aged <5 y.

METHODS

Population-based study with 7597 children aged 6-59 mo surveyed by the Brazilian National Survey on Child Nutrition. SZC was adjusted for inflammation using the Biomarkers Reflecting Inflammation and Nutritional Determinants of Anemia regression correction approach, with high-sensitive C-reactive protein, assessed according to blood collection timing (morning/afternoon) and fasting status (<8 and ≥8 h). SZC <65 μg/dL (morning collection) or SZC <57 μg/dL (afternoon collection) were classified as ZD. The analysis between associated factors and ZD used the adjusted prevalence ratio (PR).

RESULTS

After adjusting for inflammation, SZC was higher in all percentiles and varied according to collection timing and fasting status. Children who had blood collected in the morning without fasting or in the afternoon had lower SZC than those assessed in the morning with fasting. The differences in adjusted SZC according to the timing of collection and fasting status were greater in the higher percentiles of the distribution, with the greatest absolute difference observed when comparing the 95th percentile of morning fasting compared with nonfasting (20.3 μg/dL). The prevalence of ZD estimated without and with adjusting SZC for inflammation was 17.8% and 13.8%, respectively. The occurrence of diarrhea, fever, or respiratory symptoms in the 15 d before blood collection was associated with a higher prevalence of ZD (PR: 1.42; 95% confidence interval: 1.04, 1.94).

CONCLUSIONS

Adjusting SZC for inflammation and considering fasting status is important to avoid overestimating the prevalence of ZD.

[Iron supplementation effects on zinc bioavailability in a regional diet of northeastern Brazil]

The effects of supplementation with iron on the zinc bioavailability of the regional diet of northeastern Brazil (RDN), were investigated. One assay with Wistar rats, feed on RDN and control diets was carried out. The RDN diets contained 16 mg Zn/kg and levels of 35 mg, 70 mg and 140 mg Fe/kg, respectively. The control diets were prepared according to the standards of the Committee on Laboratory Animal Diets, with levels of protein, iron and zinc identical to those of RDN diets. Index of apparent absorption and zinc retained in the femur of the animals were the parameters utilized to measure zinc bioavailability. The results demonstrated that the supplementation with iron decreased the zinc bioavailability, and the effects were seen to affect diet quality and the Fe:Zn ratio. This fact must be taken into consideration in practices such as the fortying of foodstuffs and the administration of vitamin-mineral supplements to populations with nutritional deficiencies.