Millions of U.S. children have disturbingly low Vitamin D levels, possibly increasing their risk for bone problems, heart disease, diabetes and other ailments, according to two new studies that provide the first national assessment of the crucial nutrient in young Americans.
About 9 percent of those ages 1 through 21 — about 7.6 million children, adolescents and young adults — have Vitamin D levels so low they could be considered deficient, while an additional 61 percent — 50.8 million — have higher levels, but still low enough to be insufficient, according to the analysis of federal data being released Monday.
"It's astounding," said Michal L. Melamed of the Albert Einstein College of Medicine in New York, who helped conduct one of the studies published online by the journal Pediatrics. "At first, we couldn't believe the numbers. I think it's very worrisome."
Low Vitamin D levels are especially common among girls, adolescents and people with darker skin, according to the analysis of a nationally representative sample of more than 6,000 children. For example, 59 percent of African American teenage girls were Vitamin D deficient, Melamed's study found.
The researchers and others blamed the low levels on a combination of factors, including children spending more time watching television and playing video games instead of going outside, covering up and using sunscreen when they do go outdoors, and drinking more soda and other beverages instead of consuming milk and other foods fortified with Vitamin D.
"This appears to be another result of our unhealthy lifestyles, including a sedentary society that doesn't go out in the sun much," Melamed said.
The analysis and an accompanying federal study also found an association between low Vitamin D levels and increased risk for high blood pressure, high blood sugar, and a condition that increases the risk for heart disease and diabetes, known as the metabolic syndrome.
Taken together, the studies provide new evidence that low Vitamin D levels may be putting a generation of children at increased risk for heart disease and diabetes, two of the nation's biggest health problems that are also increased by the childhood obesity epidemic.
"These are very important studies," said Richard S. Rivlin, a past president of the American Society for Clinical Nutrition who was not involved in the research. "They show the number of people who have high rates of Vitamin D deficiency is really very frightening."
Other researchers urged caution.
"The bottom line is that these numbers are interesting," said Frank R. Greer of the University of Wisconsin at Madison, who served on a panel that recently doubled the American Academy of Pediatrics recommendations for daily Vitamin D intake. "But I'm not ready to make a great hue and cry until we have more data. I think we should use them for further research to determine their significance."
The findings come as the National Academy of Sciences Institute of Medicine is reviewing the federal government's official guidelines for recommended daily intake of Vitamin D. A public hearing is scheduled as part of that process at the National Academy of Sciences in Washington on Tuesday.
The most well-known health problem associated with Vitamin D deficiency is rickets, which can cause bowlegs and other bone malformations. Milk was fortified with Vitamin D in the 1930s to eliminate the disorder. But during the 1990s, doctors in several cities reported unusual numbers of cases, primarily in babies being breast-fed and mostly among African American children. A number of studies began to indicate that deficiencies might be common among adults — small studies found the same among children — and that deficiencies may be associated with a host of health problems. But the new studies are the first to examine the issue nationwide in young people.
Those who had low Vitamin D levels were more likely to have lower levels of a hormone associated with healthy bones, higher blood pressure levels and lower levels of "good" cholesterol, which helps protect against heart disease, Melamed and her colleagues found.
In the second study, Jared P. Reis of the National Heart, Lung and Blood Institute analyzed data from about 3,500 adolescents from surveys conducted between 2001 and 2004, and found that compared with those with higher Vitamin D levels, those with the lowest levels had more than double the risk of having high blood pressure and blood sugar and about four times the risk for the metabolic syndrome, a group of symptoms that increases the risk for heart disease and diabetes.
Some longtime proponents of the health benefits of Vitamin D seized on the findings to urge parents to ask doctors to test their children's Vitamin D levels, consider increasing supplementation or make sure children spend more time outdoors to boost their levels.
"The sun has been demonized for years and as a result, people have avoided any direct exposure to sunlight," said Michael F. Holick of the Boston University School of Medicine. "I think that's the wrong message."
But others said they worried that encouraging children to spend more time in the sun could lead to more skin cancer, which is already the leading type of cancer.
More on: Vitamin D