The scholars noted that children with suboptimal vitamin D blood levels did not reach optimal levels after taking nearly twice the recommended amount of the nutrient daily for six months. Vitamin D is important for calcium metabolism and bone health, said lead investigator and Children’s Hospital pediatrician Kumaravel Rajakumar, M.D., M.S., who also is an associate professor of pediatrics at Pitt’s School of Medicine. “Vitamin D deficiency is common in the northeastern U.S., especially in black children whose darker skin complexions have higher amounts of melanin, preventing absorption of the ultraviolet light that’s needed to trigger vitamin D synthesis.”
Guidelines differ on adequate blood levels of vitamin D for bone health, highlighting the need for further research. Blood level of 25-hydroxyvitamin D is the best measure of vitamin D status. For example, a blood level of 20 or more nanograms per milliliter (ng/mL) of the vitamin is considered adequate for bone health by the Institute of Medicine, while the Endocrine Society recommends a level of 30 ng/mL for optimal bone health.
Between October and March of 2008 through 2011, the researchers randomly assigned 84 black and 73 white 8- to 14-year-old children from Pittsburgh and Kittanning, Pa., to take for six months either a daily pill of 1,000 international units (IU) of vitamin D3 or a placebo. They also performed periodic blood tests to assess their 25-hydroxyvitamin D levels and other markers of bone health.
The average vitamin D level at the initial assessment of all children, and particularly black children, was suboptimal (less than 20 ng/mL), and supplementation raised their average level to above 20 ng/mL but not as high as 30 ng/mL. After six months of vitamin D supplementation in children with initial vitamin D levels less than 20 ng/mL, 39 percent remained below 20 ng/mL and only 14 percent rose above 30 ng/mL. Biomarkers of bone turnover remained unchanged.
“Our findings suggest that currently recommended daily dietary allowances of vitamin D of 600 IU may be inadequate for preventing vitamin D deficiency in children,” Rajakumar said. “It may be important to revisit these recommendations, especially since the higher dose of vitamin D used in this study was safe and did not appear to lead to any side effects.”
The project was funded by National Institutes of Health grants HD052550, DK062895, AG024827, HL112985 and RR024153; and Children’s Hospital of Pittsburgh of UPMC.