In the United States, milk has become synonymous with strong bones. It's long been a recommendation by doctors and the U.S. Department of Agriculture that everyone over eight years old include three cups of dairy in their diet every day. But over the years, experts have poked some holes in the milk-bone health connection. Is milk really all its cracked up to be?
One of the major ingredients for healthy bones is calcium. This mineral provides structural strength to bones and teeth, and helps the body perform numerous other functions, such as clot blood and transmit nerve impulses. Normally, your body gets the calcium it needs from your diet, but if that's not possible, it'll start pulling calcium from your bones, making them weaker in the process.
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It's for this reason the National Osteoporosis Foundation recommends you get between 1,000 and 1,200 milligrams of calcium every day. "Milk and dairy products are good calcium sources," says Dr. Michael Lewiecki of the New Mexico Clinical Research & Osteoporosis Center. "In general, each serving of dairy – one cup of milk, a small container of yogurt, an ounce of cheese – has 300 milligrams of calcium." This means, essentially, that you can get almost your entire daily-recommended amount of calcium just by ingesting three servings of dairy, as recommended by the USDA.
In recent years, some researchers have argued that milk can actually cause the bones to lose calcium. The "acid-ash" hypothesis proposes that digesting milk leaves behind acidic residues that make your urine (and therefore your body) more acidic; to compensate for this, the body pulls alkaline minerals, such as calcium, from the bones. In 2011, however, a pair of scientists took a hard look at the evidence for this hypothesis and found it wanting.
They explain, for example, that the pH of urine is not indicative of the body's pH. What's more, they note that some studies have found that milk consumption actually results in alkaline urine, not acidic urine.
Some experts also point out that bone fracture rates appear to be highest in countries that consume the most dairy. But the 2011 review stresses that many factors affect bone health, such as physical activity, genetics, and weight. Indeed, the higher fracture rates in those developed countries – including the U.S. – may be due to less physical labor and more sedentary lifestyles, rather than milk consumption.
Over the years, research has gone back and forth on whether milk really does help build strong bones. A recent study found that elderly men who drank a lot of milk during their teenage years actually had an increased risk for hip fractures. Another study, however, showed that milk (and yogurt) consumption results in higher bone mineral density in the hip. Overall, the majority of research suggests that dairy has some beneficial effects on bone health, in part because of milk's other nutrients.
"In terms of bone growth and health, you need a certain amount of protein, potassium, calcium, and other nutrients," says Dr. René Rizzoli, head of the Division of Bone Diseases at Geneva University Hospitals in Switzerland. "The food that contains the most well balanced amount of these things is milk and other dairy products."