A study about pollutants substances in breastmilk led by Dr. Nicolás Olea has been published this March analyzing the levels of lead (Pb), mercury (Hg), cadmium (Cd) and arsenic (As) in breastmilk samples in a milk bank in Spain (1).

This study analyzed 83 human milk samples and determined that arsenic was the most detected element, found in 97.1% of the samples analyzed with a mean concentration of 1.49 μg/L. It was followed by mercury, which was found in 81.2% of the samples analyzed with a mean concentration of 0.26 μg/L; lead, which was found in 50.6% of the samples and a mean concentration of 0.14 μg/L; and cadmium in 38% of the samples analyzed with a mean concentration of fewer than 0.04 μg/L.

Given these results, the authors concluded that it would be necessary to routinely monitor the presence of these environmental toxicants in milk and give recommendations on healthy habits to donor mothers. But is this really necessary?

It is not news that heavy metals and other contaminants have been found in breastmilk, in fact, human milk is used as an indicator of environmental pollution in the population. Despite this, breastmilk remains the optimal nutrition for newborns and contains a broad spectrum of biologically active and beneficial components for the baby. Moreover, as described in the published article, the levels of pollutants in breastmilk have decreased in recent years.

On the other hand, it has been shown in several studies that the alternative to breastmilk – artificial formula milk made mainly from cow’s or soy milk – also contains pollutants and heavy metals. The levels of these depend on the area where families live (2-10). There are areas where levels of heavy metals and contaminants in formula milk are the same or similar to those found in breastmilk, while in other regions they are found higher in formula milk than in human milk.

For example, in a study in Sweden, the daily intake of various elements in six-week-old infants drinking breastmilk and formula milk of various types was estimated (2). They found that the estimated daily intake of arsenic, cadmium, and lead in breastmilk was 0.39 µg, 0.04 µg, and 0.35 µg, respectively. In contrast, in artificial formula milk, it was significantly higher with levels of 0.65 µg, 0.11 µg and 1.1 µg and in soy-based formula milk, it was even higher reaching levels of 1.4 µg, 1.0 µg and 1.3 µg. Most formula milk used worldwide is freeze-dried and therefore, needs to be reconstituted with water. Local water quality can also contribute to increased levels of pollutants in bottle feed preparation.

On the other hand, commercial solid baby food – whose manufacturers state that it is suitable for babies from 4 months of age onwards – also contains arsenic, lead and cadmium (8). In this case, the levels of cadmium and lead are similar to those of formula milk, but the levels of arsenic depend on the ingredients on which the recipe is based. For example, rice-based porridges have much higher arsenic levels than porridges based on corn, oats, millet, spelt, buckwheat or tapioca.

Importantly, in order to protect public health, international organizations have established maximum levels of toxic elements in processed baby food and infant formula, and all levels of pollutants found in formula milk and baby food are below these maximum levels.

In conclusion, newborns and infants are exposed to pollutants such as heavy metals already during pregnancy, not only through breastmilk. Public agencies and governments should establish policies and measures to decrease the levels of contaminants and heavy metals consumed by the general population and establish recommendations for pregnant women, lactating women, infants and children, as has been done so far.

The results of pollutants monitoring in breastmilk should be treated with caution in order to establish policies that facilitate breastfeeding and do not alarm the general population. If toxic substances found in human milk are at any time above the recommended levels, public policies should focus on lowering general levels of environmental pollution to which mothers, as well as the rest of the population, are exposed to. In any case, breastfeeding remains the optimal nutrition for infants, especially considering that artificial formula milk presents similar levels of these substances.

References:

1. Freire C, Iribarne-Durán LM, Gil F, Olmedo P, Serrano-Lopez L, Peña-Caballero M, et al. Concentrations and determinants of lead, mercury, cadmium, and arsenic in pooled donor breast milk in Spain. Int J Hyg Environ Health. 2022;240:113914.
2. Ljung K, Palm B, Grandér M, Vahter M. High concentrations of essential and toxic elements in infant formula and infant foods – A matter of concern. Food Chem. 2011;127(3):943–51.
3. Iwegbue CMA, Nwozo SO, Overah LC, Nwajei GE. Survey of trace element composition of commercial infant formulas in the nigerian market. Food Addit Contam Part B Surveill [Internet]. 2010;3(3):163–71.
4. Kazi TG, Jalbani N, Baig JA, Afridi HI, Kandhro GA, Arain MB, et al. Determination of toxic elements in infant formulae by using electrothermal atomic absorption spectrometer. Food Chem Toxicol. 2009;47(7):1425–9.
5. Dabeka R, Fouquet A, Belisle S, Turcotte S. Lead, cadmium and aluminum in Canadian infant formulae, oral electrolytes and glucose solutions. Food Addit Contam – Part A Chem Anal Control Expo Risk Assess [Internet]. 2011;28(6):744–53.
6. Gundacker C, Pietschnig B, Wittmann KJ, Lischka A, Salzer H, Hohenauer L, et al. Lead and mercury in breast milk. Pediatrics [Internet]. 2002;110(5):873–8.
7. Martínez MÁ, Castro I, Rovira J, Ares S, Rodríguez JM, Cunha SC, et al. Early-life intake of major trace elements, bisphenol A, tetrabromobisphenol A and fatty acids: Comparing human milk and commercial infant formulas. Environ Res. 2019;169:246–55.
8. Ursinyova M, Masanova V. Cadmium, lead and mercury in human milk from Slovakia. Food Addit Contam [Internet]. 2005;22(6):579–89.
9. Chajduk E, Pyszynska M, Polkowska-Motrenko H. Determination of trace elements in infant formulas available on polish market. Biol Trace Elem Res [Internet]. 2018;186(2):589–96.
10. Su C, Zheng N, Gao Y, Huang S, Yang X, Wang Z, et al. Content and dietary exposure assessment of toxic elements in infant formulas from the chinese market. Foods [Internet]. 2020;9(12):1–10.