骨质疏松到底是什么原因造成的，如何预防这种现象的产生?下面的新托福考试阅读练习资料会给你解答。

　　托福阅读：Osteoporosis

　　Today’s word is: osteoporosis!

　　Yep, osteoporosis. Now, you’ve heard this word before, and you know it has something to do with bones. But can you actually explain what it is?

　　The answer is straight-forward. It comes down to the fact that we human beings need calcium in our blood–it allows us to do all sorts of neat things, from contracting muscles to conducting nerve impulses. Where to get some calcium? Food is a good idea. But what if there isn’t always calcium-rich food to be had, as was probably the case for most of our long evolutionary history?

　　Best to store some for a rainy day. Store it where? The skeleton works! Then, when the blood runs low on calcium, a signaling device called the parathyroid gland can activate a process by which calcium is taken from the skeleton and put back into the blood.

　　Which is just what happens. This is a great short-term fix, but what about the poor skeleton? Eventually it will suffer from the loss of its own calcium–bones will become brittle.

　　What can we do? Two things. Help your body get more calcium by eating fatty fish and vitamin-D rich dairy products. Why vitamin D? Because that causes the small intestine to increase its calciumuptake, bypassing the need to grab extra from the bones. Under a doctor’s supervision, calcium tablets might also be helpful, along with the old standard–more exercise. Weight-bearing exercise helps keep bones strong and less likely to fall prey to the body’s own mechanisms in later age.

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