(HealthDay News) — Rising numbers of Americans may be getting too much vitamin D via supplementation, according to a research letter published in the Journal of the American Medical Association.

Mary Rooney, MPH, of the University of Minnesota in Minneapolis, and colleagues looked at information from national surveys that included 39,243 people. The surveys were taken beginning in 1999 and continued through 2014.

The researchers found that in 1999 to 2000, 0.3% of U.S. adults took 1000 IUs or more of vitamin D daily. By 2013 to 2014, 18.2% of adults were taking that much vitamin D daily. In 2007 to 2008, 0.2% of Americans took 4000 IUs or more daily. By 2013 to 2014, that number was 3.2%. The researchers said the trends of increasing use of supplemental vitamin D were found across most age groups, genders, races, and ethnicities. People over 70 were most likely to take more than 4000 IUs daily. Women and whites were also more likely to take the higher amounts of vitamin D.

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“More may not always be better with vitamin D,” Rooney told HealthDay. “There’s not much research on longer-term health outcomes on high-dose supplements.”

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  1. Rooney MR, Harnack L, Michos ED, et al. Trends in Use of High-Dose Vitamin D Supplements Exceeding 1000 or 4000 International Units Daily, 1999-2014. JAMA. 20 July 2017. doi:10.1001/jama.2017.4392