Iodine

Iodine is an essential component of the thyroid hormones. These hormones control the regulation of body metabolic rate, temperature regulation, reproduction and growth.

The recommended iodine intake is 150 ug/d for adults [4]. Accordingly, a daily intake of 0.5 litres milk with an average content of 160 ug iodine/l meets about 50% of the requirement (Table 1). However, it is important to underline the great seasonal variation in iodine content of milk (see later).

Magnesium

Magnesium is ubiquitous in foods, and milk is a good source, containing about 100 mg/l milk [9]. Recommended intake is 400 mg/day for men and 310 mg/day for women [4]. Magnesium has many functions in the body, participating in more than 300 reactions. Magnesium deficiency has been linked to atherosclerosis, as studies have shown that deficiency may give oxidative stress [128]. Magnesium may also have a role in reducing asthma, and experimental studies of persons with asthma suggest that magnesium infusion may have a place in the acute treatment of asthma [129]. A possible mechanism may be that magnesium together with taurine dampens the signaling effects of a too high calcium release inside the cells [111,130]. Magnesium deficiency may occur following kidney disease and after use of some diuretic drugs. Magnesium deficiency in elderly is observed, and may be a result of poor appetite or unbalanced diet.

Zinc

Zinc is an essential part of several enzymes and metalloproteins. Zinc has several functions in the body, in DNA repair, cell growth and replication, gene expression, protein and lipid metabolism, immune function, hormone activity, etc [4]. Milk is a good zinc source; containing about 4 mg/l [9]. Recommended intake is 8 and 11 mg/day for adult female and male [4]. The bioavailability of zinc is better from milk than from vegetable food [4], and inclusion of milk in the diet may improve total bioavailability of zinc [131].

Vitamin E

Vitamin E concentration in milk is about 0,6 mg/l [9] (Table 1), but may increase 3–4 folds by proper feeding regimes (see later). Recommended intake is 15 mg/day [4]. Vitamin E is not a single compound; it includes tocoferols and tocotrienols. In whole milk, alpha-tocopherol is the major form of vitamin E (>85%); gamma-tocopherol and alpha-tocotrienol are present to a lesser extent, about 4 % each of the sum of tocoferols and tocotrienols [132]. Observational studies indicate that high dietary intake of vitamin E are associated with decreased risk for cancer and coronary heart disease, and that vitamin E can stimulate T-cells and increase the immune defence system. Milk seems to be a food item favouring absorption and transportation of vitamin E from ingested food into the chylomicrons [133].

Vitamin A

Milk is a good source of retinoids, containing 280 ug/l [9] (Table 1). Recommended daily intake is 700–900 ug/day [4]. Vitamin A has a role in vision, proper growth, reproduction, and immunity, cell differentiation, in maintaining healthy bones as well as skin and mucosal membranes [4].

Folate

Bovine milk contains 50 ug folate/l [9]. Studies indicate that 5-methyl-tetrahydrofolate is the major folate form in milk [134]. Recommended intake of folate is 400 ug/day for adults [4]. Many scientists believe that folate deficiency is the most prevalent of all vitamin deficiencies [4]. It is generally accepted that folate supplementation (400 ug/day) before conception and during the first weeks of pregnancy reduces the risk of neural tube defects. A recent study has shown that higher total folate intake was associated with a decreased risk of incident hypertension, particularly in younger women [135]. In addition, folates may have a protective role to play against coronary heart disease and certain forms of cancer, but sufficient evidence is not yet available [136]. The complexity of the folate metabolism suggest that different metabolites of folate are involved in different reactions, and that dihydrofolate and 5-methyl-tetrahydrofolate are the active compounds in growth-inhibition in colon cancer cells [137].

The bioavailability of folate varies [138]. Folate-binding proteins occur in unprocessed milk, pasteurised milk, spray-dried skim milk powder and whey [134]. Animal and human studies have suggested that these components enhance food folate bioavailability, and it is shown that inclusion of cow milk in the diet enhanced the bioavailability of food folate [139]. In a population-based study, the consumption of milk and yogurt were inversely associated with serum total homocysteine concentrations, and the authors explained this association by intakes of folate and riboflavin [140].