NEW YORK—Adolescents can safely take, and may need, vitamin D doses that are up to 10 times what is generally recommended, a small study suggests.
In a trial that followed 340 10- to 17-year-olds for one year, Lebanese researchers found that vitamin D doses equivalent to 2,000 IU per day were not only safe, but also achieved more-desirable blood levels of the vitamin.
The dose used in the study was 10 times the official "adequate intake" level set for vitamin D in the United States—200 IU per day for children and adults younger than 50.
An adequate intake, or AI, is set when health officials believe there is insufficient evidence to lay down a recommended dietary allowance, or RDA.
But some researchers have argued that the 200 IU standard is too low. This year, the American Academy of Pediatrics began recommending that children and teenagers get 400 IU of vitamin D each day.
In the current study, reported in the Journal of Clinical Endocrinology & Metabolism, researchers looked at whether adolescents can take doses equivalent to 2,000 IU per day without risking side effects—like nausea, vomiting, constipation, and weight loss.
Dr. Ghada El-Hajj Fuleihan and colleagues at the American University of Beirut first conducted an eight-week safety study in which 25 adolescents were given either a weekly dose of 14,000 IU of vitamin D3—also known as cholecalciferol—or a placebo.
They found that the high vitamin dose caused no toxic effects.
Then, in a longer-term study, the researchers randomly assigned 340 10- to 17-year-olds to take either 14,000 IU or 1,400 IU of vitamin D3 per week for one year.
At the end of the study, El-Hajj Fuleihan's team found, only the higher-dose group showed a significant increase in their blood levels of vitamin D—from an average of 15 ng/mL to 36 ng/mL (nanograms per milliliter).
Some experts consider a vitamin D level of 30 ng/mL or higher to be desirable for overall health.
Vitamin D has been the subject of much research of late, including one study published earlier this month showing that 40 percent of U.S. babies and toddlers may have inadequate blood levels of the vitamin.
In the Middle East, El-Hajj Fuleihan told Reuters Health, vitamin D deficiency is a major problem, and a daily dose of 2,000 IU may be necessary for many children.
Deficiencies are generally less severe in U.S. children, El-Hajj Fuleihan noted, and a dose closer to 1,000 IU might be sufficient—a question currently being studied, she said.
El-Hajj Fuleihan and her colleagues are now planning a study of 6- to 10-year-old children for whom the vitamin D dose will be equivalent to 1,000 IU per day.
Vitamin D is necessary for healthy bone development and maintenance, and it also plays a role in nerve, muscle, and immune system function.
Some studies have linked low vitamin D levels to a higher risk of type 1 diabetes in children, and in adults, a higher risk of heart disease and certain cancers.
Source: Journal of Clinical Endocrinology & Metabolism, July 2008
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