Some suggest as much as 10, 000 IU --currently the tolerable upper intake daily.

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However, he said, there's no harm in taking a 200-IU dose of vitamin D because it's difficult to get the recommended daily amount of 600 IUs from food alone for children and adults up to age 70.

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The IOF estimated that doses of 800 to 1, 000 IU (20-25 mcg) or higher may be required in older adults to prevent fractures and falls but stated that more research is necessary.

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Last month, Billboard annual series of top 21 musicians under the age of 21 listed K-pop star IU at 15th on the list which includes heavyweights in the western music business such as Miley Cyrus and Justin Bieber.

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By contrast, the government recommends a mere 200 to 600 IU a day, depending on age--what you get in two to six cups of fortified milk.

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However, Blumberg says this is within the range of most over-the-counter vitamin supplements, which deliver 100 or 400 IU daily.

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If your levels are normal, taking 2, 000 IU every other day or every third day would be fine, according to Dr. Bess Dawson-Hughes, senior scientist and director of the Bone Metabolism Laboratory at the Jean Mayer USDA HNRCA at Tufts University.

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