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PORTLAND A new study out in Portland cautions against relying on the potency of vitamin D supplements in the winter months.

Researchers with Kaiser Permanente Center for Health Research tested dozens of over-the-counter vitamin D from 12 different manufacturers in five different Portland-area stores.

More:Kaiser vitaminD study

The analysis showed amounts of vitamin D ranging from 9 percent to 146 percent of the amount listed on the label, with some even differing in pills from the same bottle.

The biggest worry is for someone who has low levels of vitamin D in their blood. If they are consistently taking a supplement with little vitamin D in it, they could face health risks, Kaiser investigators and the study s author Dr. Erin S. LeBlanc said.

Analysis was conducted by an independent lab in Houston.

The U.S. Food and Drug Administration is considering possible new guidelines for some supplements but, for the most part, the industry remains unregulated, the study said.

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