Global evidence on vitamins in human milk: A 2002-2022 systematic review with a focus on China and implications for maternal diet and infant formula.

Current knowledge on vitamin composition of human milk in China remains fragmented, with most evidence derived from small-scale studies focusing on individual vitamins. To provide a comprehensive perspective relevant to nutrition science and infant formula design, this study systematically reviewed global trends in human milk vitamins over the past two decades (2002-2022), with attention to regional disparities, maternal dietary patterns, and local standards. Literature was retrieved from PubMed, Web of Science, ScienceDirect, Chongqing VIP Information, China National Knowledge Infrastructure (CNKI), and Wanfang databases following predefined inclusion criteria. Fifty-seven studies encompassing 9833 human milk samples from 33 countries were included. Across lactation, concentrations of water-soluble vitamins generally increased, whereas fat-soluble vitamins A (VA) and E (VE) exhibited a declining tendency. Compared with Chinese samples, non-Chinese human milk contained higher levels of vitamin B1 (VB1), vitamin B6 (VB6), VA, and VE; while vitamin B5 (VB5) was consistently higher in Chinese human milk. Temporal analysis within China revealed elevated levels of VA (2016-2017), B vitamins (2014), and VE (2022), likely reflecting shifts in maternal dietary intake and nutritional awareness. Concentrations of VA, VE, VB5, and vitamin VB7 (VB7) in Chinese human milk met national adequate intake (AI) recommendations for infants aged 0-6 months. However, these concentrations remained substantially lower than the levels specified in China's national standard for infant formula. Notably, vitamin D (VD) emerged as the nutrient most vulnerable to inadequacy among exclusively breastfed infants, indicating a persistent gap between physiological supply from human milk and recommended intake. These findings emphasize the need for nationally representative, lactation-stage-specific reference ranges for human milk vitamins in China. Such evidence is essential for optimizing maternal dietary strategies, for guiding rational vitamin fortification, and formulation of next-generation infant formulas that better reflect physiological nutrition.