对于尼古丁，仅仅是1.8毫微克每毫升，太低而不易提取。

For nicotine, that level was a mere 1.8 nanograms per milliliter — too low to be picked up in tests.

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当研究对象睡眠少于6小时，他们的饥饿激素水平从每升75毫微克上升到85毫微克。

And when the study subjects were getting less than six hours of sleep a night, their ghrelin levels rose from 75 nanograms per liter to 84 ng per liter.

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在医学研究院坚持20毫微克就足够了，但是其他专家则建议标准应该高一点以确保钙质吸收最大值和骨骼健康。

The Institute of Medicine maintains that a level of 20 nanograms is adequate, but other experts say it should be higher to assure maximum calcium absorption and bone health.

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