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Milk products from cows and other nonhuman mammals are major components of traditional Western diets, especially in cold climates. The recommended intake of milk or equivalent portions of cheese, yogurt, or other dairy products in the United States is three 8-oz (237 ml) servings per day for adults and children 9 years of age or older, an amount that is substantially higher than the current average intake among adults of 1.6 servings per day.1 The recommended intake amount has been justified to meet nutritional requirements for calcium and reduce the risk of bone fractures. However, the health benefit of a high intake of milk products has not been established, and concerns exist about the risks of possible adverse health outcomes. Therefore, the role of dairy consumption in human nutrition and disease prevention warrants careful assessment.
Composition of Dairy Products
Because the natural function of milk is to nourish and promote the growth of young mammals, it contains all essential nutrients as well as multiple anabolic hormones (Table 1).3–6 To increase milk production, cows have been bred to produce higher levels of insulin-like growth factor I (IGF-I),7 and they are pregnant for most of the time they are milked,8 which greatly increases levels of progestins, estrogens, and other hormones in milk.9
Milk processing has many potential health implications. Pasteurization reduces transmission of brucellosis, tuberculosis, and other pathogens. Fermentation to produce aged cheese, yogurt, kefir, and other products denatures peptide hormones, alters protein antigens, reduces lactose content, and affects bacterial composition.10 Fractionation yields butter, reduced-fat products, and whey protein, and fortification with vitamins A and D can supplement diets.
Growth and Development
If breast milk is not available, cow’s milk (as the basis of infant formula for children younger than 1 year of age) can add important nutritional value during early childhood. However, normal growth and development can be obtained throughout childhood without dairy products if attention is given to diet quality,11 including the use of supplemental B12 in diets that include few animal products and vitamin D to compensate for low sun exposure.
Even with adequate overall nutrition, milk consumption augments longitudinal growth and attained height.12–14 Whether this growth-promoting effect is caused...