Seven out of 10 U.S. children have low levels of vitamin D, raising their risk of bone and heart disease, according to a study of more than 6,000 children.
The striking findings of researchers at Albert Einstein College of Medicine of Yeshiva University suggest that vitamin D deficiency could place millions of children at risk for high blood pressure and other risk factors for heart disease. The study is published today in the online version of Pediatrics.
Vitamin D deficiency was thought to be relatively rare in the United States. However, recent studies have documented this growing problem in adults. With cases of rickets (a bone disease in infants resulting from low vitamin D levels) rising, it became clear that many children were not getting enough of this essential vitamin, which is needed for healthy bone growth, among other biological processes.
"Several small studies had found a high prevalence of vitamin D deficiency in specific populations of children, but no one had examined this issue nationwide," said Dr. Michal L. Melamed, study leader and assistant professor of medicine and of epidemiology and population health at Einstein.
To learn more about the prevalence of vitamin D deficiency (defined as less than 15 ng/mL of blood) and vitamin D insufficiency (15 to 29 ng/mL), the researchers analyzed data on more than 6,000 children, ages one to 21, collected by the National Health and Nutrition Examination Survey 2001-2004.
The researchers found that 9 percent of the study sample, equivalent to 7.6 million children across the United States, was vitamin D deficient, while another 61 percent, or 50.8 million, was vitamin D insufficient. Low vitamin D levels were especially common in children who were older, female, African-American, Mexican-American, obese, drank milk less than once a week, or spent more than four hours a day watching TV, playing video games, or using computers.
The researchers also found that low levels of vitamin D deficiency were associated with higher parathyroid hormone levels, a marker of bone health, higher systolic blood pressure, and lower serum calcium and HDL (good) cholesterol levels, which are key risk factors for heart disease.
"We expected the prevalence of vitamin D deficiency would be high, but the magnitude of the problem nationwide was shocking," said Dr. Juhi Kumar, the lead author and a fellow in pediatrics at Children's Hospital at Montefiore Medical Center, The University Hospital and Academic Medical Center for Albert Einstein College of Medicine. Kumar will become an assistant professor of pediatrics at Weill Cornell Medical College this month.
Previous data has shown that vitamin D levels have declined during the past 20 years, Melamed said. "Kids have more sedentary lifestyles today and are not spending as much time outdoors. The widespread use of sunscreens, which block UV-B rays, has only compounded the problem."
The body uses UV-B sunlight to convert a form of cholesterol in the skin into vitamin D.
Melamed recommends that children consume more foods rich in vitamin D, such as milk and fish. "But it's very hard to get enough vitamin D from dietary sources alone," she said.
Vitamin D supplementation can help. In the study, children who took vitamin D supplements (400 IU/day) were less likely to be deficient in the vitamin. However, only four percent of the study population actually used supplements. The American Academy of Pediatrics, which recently updated its vitamin D guidelines, now recommends that infants, children, and teens should take 400 IU per day in supplement form.
"The message for pediatricians is that vitamin D deficiency is a real problem with consequences not only for bone health but also potentially for long-term cardiovascular health. Pediatricians should be screening children for vitamin D levels, especially in the high-risk populations," Kumar said.
A study in which Melamed was a co-leader and was published in the Archives of Internal Medicine in August 2008 reported that individuals with low levels of vitamin D may have an increased risk of death from all causes.
As for parents, Melamed said, "It would good for them to turn off the TV and send their kids outside. Just 15 to 20 minutes a day should be enough. And unless they burn easily, don't put sunscreen on them until they've been out in the sun for 10 minutes, so they get the good stuff but not sun damage."