Vitamin A content of human milk affected by time after delivery and by gestational age at birth

Abstract

To determine the average concentration of vitamin A in human milk according to time after delivery and to gestational age at birth, all reports of vitamin A activity in human milk during the past 40 years were reviewed. To minimize the effect of maternal nutritional status on the vitamin A content of milk, only those values from developed countries (with under 5 child mortality <20/1000 live births) were included in this study. All reports of vitamin A activity were translated into retinol equivalents (RE) to allow comparison among studies. Reported values were divided by the time after delivery during which the samples were obtained (1–6, 7–13, or 14–21 days; 1–2, 3–4, or 5–6 months). The studies were further divided by whether the birth was term or preterm (<37 weeks). There were no reports from developed countries of the vitamin A content of term milk after 6 months of lactation and no reports of the vitamin A content of preterm milk after 2 months of lactation. Because human milk changes to meet the changing needs of the growing infant, the vitamin A content changes over time. Colostrum and transitional milk are particularly rich in vitamin A activity. The weighted average vitamin A concentration (retinol plus beta-carotene) in term milk during the first week of lactation was 1654 RE/liter, approximately double the weighted average of 716 RE/liter at 1–2 months, 694 RE/liter at 3–4 months, and 780 RE/liter at 5–6 months after delivery. Preterm milk contains an even higher concentration of vitamin A activity (retinol plus beta-carotene) than term milk during the first two months of lactation. As in term milk, the weighted average concentration of vitamin A in preterm colostrum and transitional milk was much higher than in mature milk, and it remained higher for longer: 1859 RE/liter at 1–6 days, 1796 RE/liter at 7–13 days, 1420 RE/liter at 14–21 days, and 1256 RE/liter at 1–2 months. The higher concentration of vitamin A in preterm milk appears to complement the low vitamin A stores of preterm infants.