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Milk products from cows and other non-human mammals are major components of traditional Western diets, especially in colder climates. The recommended intake of milk or equivalent portions of cheese, yogurt, or other dairy products here in the U.S. is three 8-oz (237 ml) servings per day for adults and children nine years of age and older, an amount that is substantially higher than the current average intake among adults of 1.6 servings per day. 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 high intake of milk products has not been established, and concerns exist about the risks of possible adverse health outcomes.

Because the natural function of milk is to nourish and promote the growth of young mammals, it contains all the necessary nutrients and anabolic hormones. To increase milk productions, cows are bred to produce higher levels of insulin-like growth factor I (IGF-I), and they are pregnant most of the time they are milked, which greatly increases the levels of progestins, estrogens, and other hormones in milk. If breast milk is unavailable, cow’s milk (as the basis for infant formula for children younger than one year of age) can add important nutritional value during early childhood. Also, since it contains IGF-I and other natural hormones and amino acids, cow’s milk stimulates the growth of children. Tall stature is associated with lower risks of cardiovascular disease, but with higher risks of cancers, hip fractures, and pulmonary emboli (blood clots).

A central rationale for high lifelong milk consumption has been to meet calcium requirements for bone health. However, an unexplained paradox exists, namely that those with the highest intakes of milk and calcium also have the highest rates of hip fractures. Traditional thinking has long been that high milk and dairy consumption promotes bone health and prevents hip fractures, but recent studies have found just the opposite. For example, a recent study of adolescents found that there was a linear relationship between milk consumption and hip fractures later in life, with every glass consumed per day increasing the fracture risk by 9%. Milk has also been promoted as a means to weight control and obesity prevention, however studies have not found any link between them. In fact, it has been shown that consumption of low-fat milk products actually leads to greater long-term weight gain as compared to full-fat products.

In a recent comprehensive review published in the New England Journal of Medicine, the authors concluded that the recommendation to consume three or more servings of dairy foods per day is not justified. The authors concluded that guidelines for daily milk and dairy consumption should be reduced to 0-2 servings per day as calcium and vitamin D can be obtained from other foods such as kale, broccoli, tofu, nuts, beans, and orange juice. They also recommended that use of reduced-fat milk as opposed to full-fat milk should be de-emphasized, and consumption of sugar-sweetened dairy foods should be discouraged as they may lead to high rates of overweight and obesity.

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By Peter Galvin, MD

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