The researchers caution that their results are not proof of cause and effect, but rather evidence of a complex interplay between low vitamin D levels and hemoglobin, the oxygen-binding protein in red blood cells.
The investigators say several mechanisms could account for the link between vitamin D and anemia, including vitamin D's effects on red blood cell production in the bone marrow, as well as its ability to regulate immune inflammation, a known catalyst of anemia.
To capture the interaction between the two conditions, researchers studied blood samples from more than 10,400 children, tracking levels of vitamin D and hemoglobin. Vitamin D levels were consistently lower in children with low hemoglobin levels compared with their non-anemic counterparts, the researchers found. The sharpest spike in anemia risk occurred with mild vitamin D deficiency, defined as vitamin D levels below 30 nanograms per milliliter (ng/ml). Children with levels below 30 ng/ml had nearly twice the anemia risk of those with normal vitamin D levels. Severe vitamin D deficiency is defined as vitamin D levels at or below 20 ng/ml. Both mild and severe deficiency requires treatment with supplements.
When investigators looked at anemia and vitamin D by race, an interesting difference emerged. Black children had higher rates of anemia compared with white children (14 percent vs. 2 percent) and considerably lower vitamin D levels overall, but their anemia risk didn't rise until their vitamin D levels dropped far lower than those of white children. The racial difference in vitamin D levels and anemia suggests that current therapeutic targets for preventing or treating these conditions may warrant a further look, the researchers say.
"The clear racial variance we saw in our study should serve as a reminder that what we may consider a pathologically low level in some may be perfectly adequate in others, which raises some interesting questions about our current one-size-fits-all approach to treatment and supplementation," says lead investigator Meredith Atkinson, M.D., M.H.S., a pediatric kidney specialist at the Johns Hopkins Children's Center.
Untreated, chronic anemia and vitamin D deficiency can have wide-ranging health consequences, including organ damage, skeletal deformities and frequent fractures, and lead to premature osteoporosis in later life.
Long known for its role in bone development, vitamin D has recently been implicated in a wide range of disorders. Emerging evidence suggests that low vitamin D levels may play a role in the development of certain cancers and heart disease and lead to suppressed immunity, the researchers note.
Anemia, which occurs when the body doesn't have enough oxygen-carrying red blood cells, is believed to affect one in five children at some point in their lives, experts say. Several large-scale studies have found severe vitamin D deficiency in about a tenth of U.S. children, while nearly 70 percent have suboptimal levels.
"If our findings are confirmed through further research, low vitamin D levels may turn out to be a readily modifiable risk factor for anemia that we can easily tackle with supplements," says senior study investigator Jeffrey Fadrowski, M.D., M.H.S., also a pediatric kidney specialist at Johns Hopkins.
The research was funded by the National Institute of Diabetes, Digestive and Kidney Diseases under grant number K23 DK084116.
Other investigators involved in the research included Michal Melamed, M.D., M.H.S., of the Albert Einstein College of Medicine in Bronx, New York; Juhi Kumar, M.D., M.P.H., of Weill Cornell Medical College; Cindy Roy, Ph.D., and Edgar Miller III, M.D., Ph.D., of Johns Hopkins; and Susan Firth, M.D., Ph.D., of The Children's Hospital of Philadelphia.
Related article on the Web: Memo to Pediatricians: Screen All Kids for Vitamin D Deficiency, Test Those at High Risk
Founded in 1912 as the children's hospital of the Johns Hopkins Medical Institutions, the Johns Hopkins Children's Center offers one of the most comprehensive pediatric medical programs in the country, with more than 92,000 patient visits and nearly 9,000 admissions each year. Hopkins Children's is consistently ranked among the top children's hospitals in the nation. Hopkins Children's is Maryland's largest children's hospital and the only state-designated Trauma Service and Burn Unit for pediatric patients. It has recognized Centers of Excellence in dozens of pediatric subspecialties, including allergy, cardiology, cystic fibrosis, gastroenterology, nephrology, neurology, neurosurgery, oncology, pulmonary, and transplant. For more information, visit http://www.hopkinschildrens.org.
Johns Hopkins Medicine (JHM), headquartered in Baltimore, Maryland, is a $6.7 billion integrated global health enterprise and one of the leading health care systems in the United States. JHM unites physicians and scientists of the Johns Hopkins University School of Medicine with the organizations, health professionals and facilities of The Johns Hopkins Hospital and Health System. JHM's vision, "Together, we will deliver the promise of medicine," is supported by its mission to improve the health of the community and the world by setting the standard of excellence in medical education, research and clinical care. Diverse and inclusive, JHM educates medical students, scientists, health care professionals and the public; conducts biomedical research; and provides patient-centered medicine to prevent, diagnose and treat human illness. JHM operates six academic and community hospitals, four suburban health care and surgery centers, and more than 30 primary health care outpatient sites. The Johns Hopkins Hospital, opened in 1889, was ranked number one in the nation for 21 years in a row by U.S. News & World Report.
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