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Nearly 51 percent of 6,000 kids surveyed have levels that are considered insufficient while about 90 percent of kids have levels that could be considered deficient.
Researchers say various factors contribute to the condition. They include kids spending more time indoors watching television and playing video games, covering up and using sunscreen while outside, and drinking more soda as opposed to milk and other drinks that are fortified with Vitamin D.
The studies are published on-line by the journal "Pediatrics."
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