ELK GROVE VILLAGE, ILL. — "Many U.S. children need more vitamin D." That was the conclusion of a national study published in the November issue of Pediatrics.
"These data are a call to action to determine in children the optimal level of 25 (OH) D (25-hydroxyvitamin D), the health effects of vitamin D in children and the different approaches that one might use to reach a healthy level," said the authors of the study, "Serum 25-hydroxyvitamin D levels among U.S. children aged 1 to 11 years: Do children need more vitamin D?"
The study was written by a team led by Jonathan M. Mansbach of the Department of Medicine, Children’s Hospital Boston, Harvard Medical School, Boston.
The study could strengthen the voices of those in the scientific community advocating increased fortification of food products, with a possible focus on grain-based foods, with vitamin D.
A number of recent single center studies have indicated that vitamin D levels are too low, but Dr. Mansbach said no nationally representative study of children ages 1 to 11 had been done.
On the basis of this study, the team said "millions of children may have suboptimal levels of vitamin D, especially non-Hispanic black and Mexican American children."
Data were obtained from the 2001-04 National Health and Nutrition Examination Survey. In the study, children were placed in three groups with serum levels below 25 nmol/l (nanomoles per liter), less than 50 and less than 75.
The mean serum level was 70 nmol/l. The prevalence of vitamin D serum levels beneath 25 nmol/l was 0.7%; beneath 25 nmol, 15%; and beneath 75, 65%. Among non-Hispanic black children, vitamin D deficiency (if measured as less than 75 nmol/l) was 89%; Mexican American children, 77%; and non-Hispanic white children, 54%.
More than half the paper was devoted to discussion of the findings, with considerable analysis of recent studies about the potential consequences of vitamin D deficiency. Also included was discussion about the state of supplementation with vitamin D.
"These data highlight that millions of children in the United States have vitamin D levels some experts consider too low and that non-Hispanic black and Mexican American children have the lowest levels," Dr. Mansbach said. "Practitioners caring for children should become aware of the emerging data bout the diverse health effects of vitamin D and understand that this group of children may require more vitamin D than they are currently making from sunlight or consuming in their diet (including supplements)."
Dr. Mansbach noted that past interest in vitamin D centered principally on the risk of rickets, a disorder long known to be caused by a lack of vitamin D, calcium, or phosphate. Rickets leads to softening and weakening of the bones.
Data increasingly show, though, that vitamin D receptors exist not only in bones but throughout the body.
"As a result, health outcomes beyond rickets are now being considered when experts and national panels try to define a health level of vitamin D for children."
Regarding bone health, Dr. Mansbach cited a 2008 study that indicated "evidence of bone demineralization" among infants and toddlers with serum vitamin D levels beneath 50 nmol/l.
"Considering non-bone health outcomes, a meta-analysis shows that the risk of type 1 diabetes is significantly reduced in children receiving vitamin D supplements compared with those not receiving supplements," the study said. "Respiratory outcomes have also been investigated. Children aged 2 to 60 months hospitalized with acute lower respiratory tract infection had a 12.5-fold higher unadjusted odds of having a vitamin D serum of less than 50 nmol/l compared with healthy controls."
Dr. Mansbach cited separate studies from the United States and Scotland demonstrating that lower maternal intake of vitamin D during pregnancy is associated with increased risk of recurrent wheezing in the mothers’ children.
In New Zealand, an inverse relationship was found between vitamin D in the umbilical cord blood and parent-reported respiratory infection (e.g., bronchiolitis, croup, pneumonia, throat infections, and ear infections) by 3 months of age and parent-reported wheezing illness at 15 months, 3 years, and 5 years of age.
"Unlike the bone outcomes, the mechanism underlying the association with vitamin D and risk of infections is less clear, although the innate immune system seems to play a role," Dr. Mansbach said.
While acknowledging less of a connection with their study of vitamin D levels in children, Dr. Mansbach also cited results of studies on vitamin D and adults. One showed a higher survival rate for colorectal cancer patients who had higher vitamin D serum levels. Another showed a lower risk of heart attack among subjects with higher vitamin D levels.
Discussing vitamin D supplements, Dr. Mansbach notes that toxicity from excessive intake may be a risk.
"Appropriately designed studies may need to be conducted to examine if excessive vitamin D supplementation either causes less overt complications than those currently recognized or long-term negative effects on adult-onset diseases.
At present, only one child in three is taking a supplement that contains vitamin D. Among those taking supplements, 5% had vitamin D serum levels beneath 50 nmol/l and more than half had levels beneath 75.
"Higher supplement doses may be required for children to reach the safe and potentially healthier levels of vitamin D of greater than 50 or greater than 75 nmol/l," Dr. Mansbach said.