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。
The Institute of Medicine recommends 600 units a day for everyone from age 1 to 70 and 800 units for men and women 71 and older, with a safe upper limit for everyone over the age of 9 of 4,000 units.
医学研究院建议年龄1岁到70岁的每人每天600单位；超过71岁的人每人每天800单位；4岁以上的人每天摄取量的安全上限为4000单位。
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。
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