Much attention needs to be paid to the studies on side effects of iodine ard the safe upper limit of iodine intake.
过量碘摄入的负效应问题，以及磺摄入量的安全上限研究应当得到足够的重视。
But while higher is better from a fuel conservation perspective, there is an upper limit on how high it is safe to orbit humans for long periods.
越高耗费的燃料越少，而载人飞船能够长时间安全飞行的轨道高度就有上限。
No exercise recommendations across the globe mention an upper limit for safe exercise, but perhaps there is one.
目前，全球尚无有关安全锻炼的上限建议，但或许应该有一个。
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