MONDAY, Aug. 3, 2009 (HealthDay News) -- Most American youngsters aren't getting enough vitamin D, and that deficiency is associated with an increased incidence of risk factors for cardiovascular problems such as heart attack and stroke, two new studies find.
Simultaneous publication of both papers in the Aug. 3 online edition of Pediatrics is coincidental, the lead authors of the reports said. Both used U.S. data from the 2001-2004 National Health and Nutrition Examination Survey, and both were initiated because of a lack of information about the possible effects of low vitamin D levels on cardiovascular risk in young people.
While studies have linked vitamin D deficiency to increased risk in American adults, "few studies have looked at whether vitamin D can be associated with increased cardiovascular disease in children," said Jared P. Reis, who began his study while at Johns Hopkins University. He is now an epidemiologist in the division of cardiovascular sciences of the U.S. National Heart, Lung, and Blood Institute.
"Nobody questions that vitamin D deficiency causes rickets," said Dr. Michal L. Melamed, an assistant professor of medicine and epidemiology at Albert Einstein College of Medicine in the Bronx, who led the other study. "We wanted to explore other health outcomes and noticed that nobody had described this outcome."
The study she led looked at the overall incidence of low blood levels of vitamin D among young Americans aged 1 to 21 in the survey. There is no formal definition of vitamin D deficiency, Reis said, but many experts believe that a level of 30 nanograms per milliliter of blood is desirable.
The Melamed study found that 9 percent of young Americans -- 7.6 million -- were vitamin D-deficient, with blood levels under 15 nanograms per milliliter, and that 61 percent -- 50.8 million -- were vitamin D-insufficient, with levels between 15 nanograms and 29 nanograms per milliliter.
The high incidence of vitamin D deficiency was so surprising that "we sat on our data for six months," Melamed said. "We didn't publish until it was confirmed by other people that we had the right numbers."
Children with the lowest vitamin D levels were more likely to have higher blood pressure, high blood sugar levels and low blood levels of HDL ("good") cholesterol, the study found.
It's not entirely certain that low levels of vitamin D early in life will translate into health problems in the adult years, Melamed said. "But if you have hypertension [high blood pressure] at age 20, you have 60 more years of dealing with the consequences," she noted.
The study led by Reis was a detailed cross-sectional analysis of data on 3,577 adolescents. It found an average vitamin D blood level of 24.8 nanograms per milliliter. The average level was 15.5 nanograms per milliliter in blacks, 21.5 in Mexican Americans and 28 in whites.
There was a clear association with cardiovascular risk factors. The 25 percent of youngsters with the lowest levels of vitamin D were 2.36 times more likely to have high blood pressure, 54 percent more likely to have low HDL cholesterol levels, 2.54 times more likely to have elevated blood sugar levels and 3.88 times more likely to have metabolic syndrome, a constellation of risk factors including obesity, high blood fats and high blood pressure.
But the results should not panic parents, Reis said. "I believe we need additional research," he said. "Our study is observational, and we need additional studies to confirm it."
Specifically, parents need not turn to supplements to provide the recommended intake of vitamin D, currently set at 200 International Units a day for everyone up to age 50, Reis said. Adequate vitamin D intake can be achieved with 15 minutes a day of exposure to sunlight or consuming fortified milk, bread and other wheat products, among other foods, he said.
"Parents should focus on modifiable risk factors," Melamed said. "Children should not always be on the computer or watching television. They can drink more milk, rather than using supplements."
Sources and effects of vitamin D are described by the U.S. National Library of Medicine.