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Throughout their lives, humans ingest many essential dietary minerals vital to their health and well-being through a large variety of consumer products, with calcium representing one of the most important factors influencing bone growth and strength. For example, the bioavailability of calcium and other proteins and nutrients in infant formula is essential for many neonates, as the first months after birth infants obtain calcium exclusively through either human milk or infant formula. Although the World Health Organization recommends for infants to be fed with only human milk, in practice this only holds true for about 38% globally. To compensate for the lower bioavailability of calcium in cows’ milk based infant formula compared to human milk, infant formula is supplemented with a higher amount of calcium. However, while the elemental composition of both types of milk and infant formula is well established, research suggests that the product matrix effect is also essential to take into account when determining the release and uptake of nutrients like calcium. For example, the calcium is contained in different molecular forms within milk casein micelles, and the casein:whey ratios greatly vary between both types of infant milk. Of course there are also other applications for being able to have a higher calcium bioavailability in milk, for example in developing countries where it is sometimes difficult for people to obtain all the minerals they need in their food. Where many studies have been devoted to the matrix effects on the bioavailability of many plant-based foods, there is still very little known about the calcium bioavailability in human milk and infant formula. Clearly, a greater understanding of the availability of calcium contained in different types of milk is required to be able to provide infants with the best available source of calcium in formula milk.


It is therefore important to investigate the bioavailability of essential minerals such as calcium, and also iron, in for cows’ and infant formula milk. The radioactive calcium isotope 45Ca can be used as a tracer to study the exchange of calcium from these milk sources, which are naturally present in the milk casein micelles, but also artificially added to the formula milk. 45Ca has a relatively long half-life (163 days), which allows for time-dependent exchange studies. This project aims to obtain a better understanding of the exchange behavior of essential elements like calcium in milk, to be able to increase their bioavailability. 

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