(LB03-27-26) Vitamin B2 Status and Relationships Among Plasma, Functional and Urinary Biomarkers Among Women of Reproductive Age in Rural Bangladesh

Objectives: Vitamin B2 (riboflavin) supports energy metabolism, antioxidant defense and erythropoiesis. Circulating riboflavin is converted intracellularly to the redox enzyme cofactors flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD). Erythrocyte glutathione reductase (EGR) is a FAD-dependent enzyme; its activity coefficient (EGRAC) indicates functional riboflavin status. Free riboflavin is the major flavin form in urine. We assessed vitamin B2 status in women of reproductive age (WRA) in rural Bangladesh with urinary riboflavin and EGRAC and examined their relationships to plasma riboflavin, as the circulating riboflavin pool.

Methods: Data were used from the baseline visit (pre-supplementation, n=285) of the Micronutrient Dose Response (MiNDR) trial, in which WRA (18–35 years) were given four levels of riboflavin with other micronutrients for 3 months. Plasma and urinary (insufficiency, < 80μg/g creatinine) free riboflavin were measured by Ultra-Performance Liquid Chromatography (UPLC) with fluorescence detection. EGRAC was measured in washed erythrocytes as the ratio of enzyme activity with and without added FAD (insufficiency, EGRAC >1.3). Due to skewness, median regression and Spearman correlation were used to explore relationships of urinary riboflavin and EGRAC to plasma riboflavin.

Results: Vitamin B2 insufficiency was 90.8% by urinary riboflavin [median (IQR) 3.95 (2.12, 18.22) μg/g creatinine] and 90.2% by EGRAC [1.91 (1.57, 2.36)]. Urinary riboflavin, although low, was positively associated with plasma riboflavin [β (95%CI) 0.31(0.059, 0.55); p=0.02] with a correlation coefficient ρ=0.23 (p=0.0001). EGRAC was not associated with plasma riboflavin [-0.004 (-0.011, 0.002), p=0.20] or urinary riboflavin in regression analyses [-0.00005 (-0.0004, 0.0003), p=0.76], but modest inverse correlations were observed (ρ=-0.16, p=0.007;ρ=-0.24, p=0.00006).

Conclusions: Vitamin B2 insufficiency was high in rural Bangladeshi women. Urinary excretion was closely aligned with concurrent circulating riboflavin, while functional status by EGRAC likely reflected tissue-level saturation that may be buffered from short-term variation in riboflavin availability. Future analysis of responses to supplementation will further inform riboflavin biomarker dynamics.

Funding Sources: Gates Foundation, Seattle, WA