主题：【一唵谈】喝牛奶会导致骨质疏松吗？ -- 唵啊吽

http://www.hsph.harvard.edu/nutritionsource/calcium.html

Getting enough calcium

Despite the debates surrounding milk and calcium, one thing is clear: adequate calcium - both for bone development and for non-bone functions - is key to reducing the risk of osteoporosis. However, the healthiest or safest amount of dietary calcium hasn't yet been established. Different scientific approaches have yielded different estimates, so it's important to consider all the evidence.

Balance studies - which examine the point at which the amount of calcium consumed equals the amount of calcium excreted - suggest that an adequate intake is 550 mg/day. To ensure that 95 percent of the population gets this much calcium, the National Academy of Sciences established the following recommended intake levels:

1,000 mg/day for those age 19-50

1,200 mg/day for those age 50 or over

1,000 mg/day for pregnant or lactating adult women

But most balance studies are short-term and therefore have important limitations. To detect how the body adapts to different calcium intakes over a long period of time - and to get the big picture of overall bone strength - requires studies of longer duration.

The results from such long-term studies may be surprising to some. While they do not question the importance of calcium in maximizing bone strength, they cast doubt on the value of consuming the large amounts currently recommended for adults.

In particular, these studies suggest that high calcium intake doesn't actually appear to lower a person's risk for osteoporosis. For example, in the large Harvard studies of male health professionals and female nurses, individuals who drank one glass of milk (or less) per week were at no greater risk of breaking a hip or forearm than were those who drank two or more glasses per week.(2, 3) Other studies have found similar results.

Additional evidence also supports the idea that American adults may not need as much calcium as is currently recommended. For example, in countries such as India, Japan, and Peru where average daily calcium intake is as low as 300 mg/day (less than a third of the US recommendation for adults, ages 19-50), the incidence of bone fractures is quite low. Of course, these countries differ in other important bone-health factors as well - such as level of physical activity and amount of sunlight - which could account for their low fracture rates.