The study – the first to investigate concentrations of iron and zinc in human milk in correlation with maternal factors like age, diet and nutritional status – found that the maternal diet influences the iron and zinc content of breast milk.
“Our results show that maternal diet influences iron and zinc content in human milk, suggesting that adequate intake of food rich in investigated minerals may be a positive factor for their concentrations in human milk,” wrote the researchers in Nutrients.
Consumption frequency of meat, vegetables and legumes was revealed to be a significant factor influencing zinc concentration, while for iron levels, it was meat, fish and seafood, vegetables, legumes, nuts and seeds that made a difference.
Tackling mineral deficiencies
The findings are significant because both iron and zinc play an essential role in many physiological processes, yet deficiencies of both minerals are a public health concern during pregnancy and infancy, especially in developing countries.
Iron is part of haemoglobin and a structural component of a variety of enzymes crucial for a range of human metabolic processes. Infants are particularly susceptible to the consequences of iron deficiency due to rapid growth and brain development.
Zinc plays a catalytic role in each of the six classes of enzymes as well as having an important involvement in the regulation of gene expression, signal transduction and neuronal transmission. Zinc deficiency in infants results in stunted growth and compromised immune function, with increased mortality from respiratory infections and diarrhoea. Zinc deficiency is reported to be responsible for 4.4% of deaths in children aged six months to five years.
Whilst the influence of maternal factors on the quality and quantity of breast milk produced is well researched, the impact of maternal diet on iron and zinc concentrations does not have well defined effects. This pilot study, therefore, investigated the link between maternal factors and iron and zinc concentrations in human milk.
Milk samples were collected between 4-6 weeks postpartum from 32 healthy, exclusively breastfeeding mothers.
Their diets were assessed via two methods: current and habitual intake. For assessing current intake, participants were required to keep dietary records for three days before milk samples were obtained. Food frequency questionnaires were then used to assess the consumption frequency of selected food items over the three months prior to the study. Nutritional status was assessed via BMI and body composition analysis.
Milk samples were collected one day before the body composition analysis and on the third day of the three-day diet records.The researchers calculated daily milk intake by weighing the infants, and the iron and zinc concentrations in the milk were determined by inductively coupled plasma mass spectrometer.
Performing multi-variable regression analysis, the researchers reported that maternal total zinc and iron intake (diet + supplementation) positively influenced their concentrations in human milk.
The models evaluated the impact of selected variables on iron concentration in milk and infants’ iron intake. These found that: “consumption frequency of food rich in iron (meat, fish and seafood, vegetables and legumes, nuts and seeds) and maternal total iron intake (diet + supplementation) were identified as significant factors influencing iron concentration in human milk and infants’ iron intake”.
The researchers said these results suggest that maternal iron supplementation may increase its concentration in human milk.
While iron supplementation can inhibit the absorption of other micronutrients, including zinc, in this study, it did not appear to influence the level of zinc in the milk.
A similar modelling exercise for zinc concluded that “consumption frequency of meat, vegetables and legumes and total zinc intake affected human milk zinc concentration”.
Overall, the study indicated that maternal diet influences iron and zinc in human milk, concluded the researchers.
“Interestingly, a positive correlation was found only with their total dietary intake (diet + supplementation), indicating that maternal supplementation may be a positive factor for iron and zinc content in human milk,” they noted.
Since the study was conducted with a small sample size, the researchers recommend further larger scale studies to investigate critical dietary factors that are associated with iron and zinc concentrations.
Authors: Agnieszka Bzikowska-Jura, Piotr Sobieraj, Magdalena Michalska-Kacymirow, Aleksandra Wesołowska
“Investigation of Iron and Zinc Concentrations in Human Milk in Correlation to Maternal Factors: An Observational Pilot Study in Poland”