Evaluation of serum retinol, the modified-relative-dose-response ratio, and breast-milk vitamin A as indicators of response to postpartum maternal vitamin A supplementation

Conflicting results have been reported regarding the relative performance of serum retinol, the modified-relative-dose-response (MRDR) ratio, and breast-milk vitamin A concentrations in detecting changes in maternal vitamin A status. We used receiver operating characteristic analyses and standardized differences to compare the ability of these indicators to detect a response to postpartum vitamin A supplementation in lactating Bangladeshi women. At 2 wk postpartum, women were randomly assigned to receive either a single dose of vitamin A [200000 IU (60000 retinol equivalents); n = 74] or placebo (n = 73). Data from maternal serum and breast milk collected 3 mo postpartum and from infant serum collected 6 mo postpartum were used to examine the ability of serum retinol, the MRDR ratio, and breast-milk vitamin A to discriminate between individuals in the supplemented and unsupplemented groups. Breast milk was collected by expressing the entire contents of one breast that had not been used to feed an infant for > or =2 h (full samples) or without controlling the time since the last breast-feeding episode (casual samples). Casual breast-milk samples performed better than full breast-milk samples in detecting a response to maternal supplementation. The MRDR ratio performed better than serum retinol in both the women and their infants. Overall, the most responsive indicator was the measurement of breast-milk vitamin A per gram of fat in casual breast-milk samples. Breast-milk vitamin A and the MRDR ratio are responsive indicators of vitamin A status, especially in women with mild vitamin A deficiency.