- Lutein is a vitamin A-like compound that appears to be important in the development of the brain and eyes in fetuses and infants.
- Lutein is passed from mother to the fetus via the placenta, and from mother to infant via human milk.
- While esters of compounds such as lutein are more common in colostrum than in mature milk, lutein is present in mature milk in far greater quantities than in infant formula.
Everyone knows that fruit and vegetables are crucial components of a healthy diet, but few have heard of lutein, a substance that is structurally similar to vitamin A and found in spinach and kale. Because the human body cannot make lutein, the amount that one swallows determines how much is available to protect the skin from ultraviolet light, lower the risk of some cancers, and—if relevant—moderate the progression of atherosclerosis. There is also mounting evidence that lutein is important in fetal and infant development. Fetuses and infants receive lutein directly from their mother—via blood that passes through the placenta and by consuming human milk.
The reasons lutein appears to be necessary for fetuses and infants are, in the main, the proper development of the brain and the eyes. Lutein’s mechanistic role in the expansion and maturation of the very young brain is not well understood, although it has been well established that the substance is concentrated in areas associated with learning and memory: the hippocampus, and the frontal and occipital cortices . In the eye, lutein (along with its isomer, zeaxanthin) constitutes the yellow pigment at the central part of the retina known as the macula, where color vision is at its keenest. Being yellow, this part absorbs energetic blue light, and therefore protects retinal cells from harmful rays. Lutein supplementation has indeed been shown to reduce the occurrence of retinopathies in premature infants  and is known to lower the odds of adults developing macular degeneration .
Lutein’s probable role in neurodevelopment recently motivated Simonetta Picone of Policlinico Casilino, in Rome, Italy, and her colleagues to measure its levels in the arterial blood of umbilical cords . The study, published in late 2017, found more lutein in the arterial cord blood of healthy infants born at 33–36 weeks than in the arterial cord blood of healthy infants born at any point after 37 weeks when lutein levels started to progressively decrease. Picone and her colleagues argue that these results are consistent with a role for lutein in brain development since its varying supply mirrors the timing of increases in brain volume and weight. Curiously, the study also identified sex differences in the levels of lutein. Among both the preterm and term infants, females received higher levels of lutein supplied through the umbilical cord.
Determining and making sense of the amount of lutein in human milk is far from a straightforward business. This is largely because the lutein in milk has a tendency to degenerate during storage. How best to measure milk lutein and just how much it degenerates when subjected to different storage techniques were the central questions of a 2017 study by Jing Tan of Abbott Nutrition Research and Development in Singapore and her colleagues based at nearby universities . They found that it perished quickly as a result of human milk being frozen and then defrosted, but that chilling at 8ºC for a couple of days did not compromise milk’s lutein content.
This advice was heeded by a team in Seville, Spain, who set out to quantify the esterified xanthophyll content of colostrum—a sugary milk produced during the first three to five days after giving birth. (Xanthophylls are a group of compounds of which lutein is a prominent member.) The researchers then sought to compare colostrum’s content to that of mature milk  and recruited 30 women for the task, all of whom visited the neonatology unit of the city’s Virgin del Rocío University Hospital. Some of these women gave birth early (defined as a 30 to 36-week pregnancy), and some gave birth at term (that is, had pregnancies lasting between 37 and 42 weeks). Colostrum samples were collected in the days immediately after their infants were born, and mature milk samples were collected 15 days after.
On analyzing the samples, the investigators found that about a third of the xanthophyll content of colostrum was present as esters—and that colostrum was rich in these esters, whereas mature milk was not. Why this would be appears to hang on the secretion of milk fat globules into milk. If xanthophyll esters are distributed on the surface of milk fat globules of colostrum but not of mature milk, the researchers argue that this indicates the gradual accumulation of these esters in the mammary epithelium, from which the globules’ membranes are derived. Once lactation gets going, however, the lipid constituents of milk fat globules increasingly reflect those molecules that were most recently added to the mammary epithelium. And because the addition of xanthophyll esters requires the completion of various biochemical processes, there simply isn’t the time to restock the mammary epithelium as milk is made.
Why esters of lutein might be functionally relevant in the first few days of life is unclear. Meanwhile, non-esterified lutein is certainly present in mature human milk, and far more so than it is in infant formula. Indeed, the only infant formulas that contain any lutein are thought to be those manufactured using egg yolk as a source of lipid, and their median lutein content per gram of fat has been found to be a quarter of that typically found in human milk . These findings are already leading researchers towards the development of lutein supplements, with initial indications proposing casein proteins from goat’s milk as superior to those from cow’s milk at improving lutein’s solubility and hence its stability in storage . But with those results just months old, the most straightforward way to ensure that an infant is getting enough lutein is for a breastfeeding mother to keep eating her greens.
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