- Carotenoids are pigments found in fruits and vegetables and have various functions in the human body.
- The levels of different carotenoids in a woman’s diet are reflected in her breast milk.
- A recent study comparing Chinese, Mexican, and American women’s breast milk identified national differences in breast milk carotenoid composition, indicating national dietary tendencies.
One of the marvels of breast milk is that its composition stays roughly the same, even when working mothers have lopsided diets, or mothers in poor places cannot find enough to eat. That much is at least true for overall levels of the major components—the fats, proteins and sugars in milk. However, recent research has suggested that chemicals called carotenoids—natural pigments found in fruits and vegetables—appear in breast milk according to how much of them a mother eats. And when compared across countries, by some measures, American moms do a fairly poor job of providing their suckling infants with them.
The research in question appears in a paper by Tristan Lipkie of Purdue University, in Indiana, and his colleagues. They set about collecting samples of breast milk from mothers living in Shanghai, Mexico City, and Cincinnati. On comparing the types and levels of carotenoids in these milk samples, the team first confirmed that no matter where a mother lives, different individuals produce very different amounts of carotenoids; if a mother is a relatively low carotenoid producer or a relatively high one, her levels tend to stay low or high throughout lactation. Providing that women are generally creatures of habit when it comes to food, this finding is consistent with the idea that mothers’ dietary norms are crucial.
In all three countries, lutein was the carotenoid with the highest levels in breast milk, but mothers in China had far more of it than mothers in Mexico or the US—most likely because Chinese people tend to eat more green vegetables. The other common carotenoids in milk were in all cases β–carotene, β-cryptoxanthin, and lycopene. Of these, lycopene also showed a strong trend: it was typically found at relative high levels in the breast milk of the mothers from Cincinnati, probably because Americans consume quite a lot of tomatoes. Generally, the breast milk of the Mexican mothers had intermediate carotenoid content compared to the Chinese and American sample—although some had notably high levels of β-cryptoxanthin, which is found in papayas and oranges.
To confirm that carotenoids were coming from the diet, and not, say, made by the mammary gland, the researchers checked that the carotenoid levels found in the US mothers’ blood plasma correlated with the levels in their breast milk, and that this also correlated with the amounts found in infants’ blood plasma. Broadly speaking, they did correlate.
So, what does this all mean in terms of possible health impacts on Chinese, Mexican, and American infants? One approach to that question is to consider the roles of individual carotenoids. One form of lutein has been found in the retina, suggesting a role for it in eye development. Thus the retinas of Chinese infants appear to be better provided for than those of Mexican or American infants. Lycopene is known to play a role in immune system development, particularly in protection against inflammatory diseases; in this case, American infants seem to be better provisioned. But that is not to say that Chinese infants will suffer from inflammatory diseases or that US infants will develop eye problems. Even at the lower end of the scale, mothers’ milk may provide enough of these compounds to furnish healthy development.
The issue of how much of the different carotenoids is required for proper development is intriguing, however, and warrants further investigation. Moreover, given that the authors found decreasing levels of carotenoids over the course of lactation, feeding wet-nursed or milk bank-supplied infants milk that is appropriate for their stage of development may come to be seen as increasingly important. Of course, that decrease might not mean that older babies are getting fewer carotenoids; they could actually get the same amount because they drink more milk. But whatever the situation, Lipkie’s study is a reminder to all breastfeeding women to make sure they get enough fruits and vegetables—and for American women in particular, to eat more greens.
1. Tristan E. Lipkie et al. 2015. Longitudinal Survey of Carotenoids in Human Milk from Urban Cohorts in China, Mexico, and the USA. PLoS ONE. 10(6): e0127729
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