Accurate estimates of vitamin A status is necessary in order to appropriately supplement children with deficiency and avoid causing hypervitaminosis A. The retinol isotope dilution method is considered the most sensitive indirect measure of total liver vitamin A reserves. Recent literature has suggested that inflammation can lead to an overestimation in the prevalence of vitamin A deficiency. However, it is not clear if inflammation impacts estimates derived from the retinol isotope dilution method. Work by Suri and colleagues describing the impact of inflammation on this technique for estimating vitamin A status is reported in the March 2023 issue of The Journal of Nutrition.
Observations (n = 532) from five studies conducted in Burkina Faso, Cameroon, Ethiopia, South Africa, and Tanzania were used to determine the association between total body vitamin A stores and total liver reserves estimated using retinol isotope dilution, and markers of inflammation (CRP and a1-acid glycoprotein, AGP). Inflammation categories were normal or elevated CRP or AGP, and the inflammation stages were reference, incubation (elevated CRP), early convalescence (elevated CRP and AGP), and late convalescence (elevated AGP).
Total liver vitamin A reserves ranged from 0.12 µmol/g in Ethiopia to 1.10 µmol/g in South Africa. Elevated CRP ranged from a high in Cameroon (42%) to a low of 4% in Burkina Faso, and elevated AGP was present in 58% of children in Cameroon to a low of 20% in Tanzania. A negative correlation between total body stores of vitamin A and AGP existed when results from Cameroon were excluded. Total body stores were impacted by infection stage but the correlations between total liver reserves and either CRP or AGP were not significant. These results led the authors to conclude there is no systemic bias in retinol isotope dilution estimates for total liver reserves caused by inflammation. However, they did suggest the inverse relationship between total body stores and AGP may be caused by an effect on isotope partitioning or reflect decreased stores after an infection.
In an editorial, Wieringa and Thurnham, describe the importance of the BRINDA project to permit use of regression analyses that generate a more gradual effect that corrects for the impact of inflammation on nutrient status. Because heterogeneity in the current study prevented use of the BRINDA method, the existing Thurnham method was used to confirm that inflammation had essentially no impact on liver stores of vitamin A. They argue that although the study supports use of the retinol isotope dilution method in populations with high inflammation status, the key outcome was the results confirm existing assumptions that correcting biomarkers of vitamin A status for inflammation provides a better estimate of vitamin A status.
Suri DJ, Sombié OO, Zeba AN, Nama GM, Bekele TH, Woldeyohannes M, et al. Association between biomarkers of inflammation and total liver vitamin A reserves estimated by 13C-retinol isotope dilution among preschool children in 5 African countries. Journal of Nutrition, Volume 153, Issue 3, March 2023, Pages 622-635. https://doi.org/10.1016/j.tjnut.2022.10.012.
Wieringa FT, Thurnham DI. Inflammation, biomarkers, and real nutritional status. Journal of Nutrition, Volume 153, Issue 3, March 2023, Pages 605-607. https://doi.org/10.1016/j.tjnut.2023.01.007.
FIGURE 2 (Featured Image) Relationship between median TBSs (μmol) (A) and TLRs (μmol/g) (B) with CRP (mg/L) or AGP (g/L) aggregated by country. The size of the circle reflects the number of subjects from that country: Burkina Faso: n = 90; Cameroon: n = 45; Ethiopia: n = 123; South Africa: n = 88; and Tanzania: n = 93. AGP, α1-acid glycoprotein; TLRs, total liver vitamin A reserves.