For nicotine, that level was a mere 1.8 nanograms per milliliter — too low to be picked up in tests.
对于尼古丁，仅仅是1.8毫微克每毫升，太低而不易提取。
Optimal levels range from 30 nanograms per milliliter to 40 nanograms per milliliter, the researchers said.
研究人员说，最佳水平范围是每毫升30到40纳克。
According to the American Cancer Society, most men have levels under 4 nanograms per milliliter of blood (ng/ml).
根据美国癌症协会的说法，大多数男性PSA含量为4ng/ml。
There were also fewer people with vitamin D levels of 30 nanograms per milliliter or higher (45 percent vs. 23 percent).
维生素d水平在每毫升30纳克或更高的人数也较少(45%和23%)。
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.
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。
When they found the treated mice were able to withstand that dose, they continued to raise it until they reached 125 nanograms, and the mice still withstood it.
当他们发现治疗后的小鼠能够耐受住这个剂量时，他们不断提高剂量直到达到125纳克，而小鼠仍然能够承受。
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.
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.
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。
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