Influence of enrichment with vitamins and minerals on the bioavailability of iron in cows' milk.

Iron is an essential element for humans and physiological needs are determined by obligatory loss, growth, menstruation and pregnancy. Although iron metabolism occurs in a ‘closed circuit ’, physiological losses occur and they must be made good. Three factors are important in the study of iron needs: the total amount of iron in the diet; the nature of the iron compound; and other components of the diet (Hallberg et al. 1998). Although iron deficiency ensues if insufficient iron is absorbed to meet requirement, the total iron absorbed normally exceeds requirement (Hallberg et al. 1997; Jackson, 1997). That only 5–15% of the iron in food is actually absorbed is a phenomenon specific to humans (Charlton & Bothwell, 1983). Ferrous forms are absorbed more efficiently than ferric forms (Boccio et al. 1997). Certain components of food affect absorption of non-haem iron: fructose, ascorbic acid (Ballot, 1987; Hurrel, 1992), fumarate and some amino acids increase iron absorption (Taylor et al. 1986). On the other hand, tannins (in tea, for example) (Tuntawiroon, 1991), polyphenolic compounds (coffee) (Morck et al. 1983; Brune et al. 1989), phytates (Hallberg et al. 1987), phosphates and cellulose plant fibre inhibit absorption of non-haem iron (Rossander et al. 1992). The action of HCl in gastric juice is also essential for absorption of non-haem iron (Hurrell, 1992). Milk contains components necessary for a nutritionally balanced and healthy diet (Favretto & Marletta, 1989; Coni et al. 1995). In some population groups, such as children and the elderly, it may constitute the main food (Ziegler & Fomon, 1996). It may be an important dietary source of minerals such as calcium and phosphorus. In the present study we determined the amount of iron in 40 milk samples including whole, skimmed and low-fat milk, milks enriched with vitamins and minerals, and dairy products. Atomic absorption spectroscopy with electrothermal atomization (ETAAS) was the analytical technique used. We also estimated the influence of enrichment of milk with minerals such as Ca on iron bioavailability using an in vitro assay to determine the absorbable fraction of the element.