Background: Vitamin D deficiency is a growing problem in the United States. A 2004 study reported that 42 percent of otherwise healthy children in a primary care setting were vitamin D deficient. Among infants, dark skin pigmentation and breastfeeding without supplementation have been cited as risk factors. Most studies have examined infants, but there are fewer data as to whether this problem persists as children are weaned to fortified milk and solid foods. Gordon and colleagues studied a group of healthy children to determine the prevalence of vitamin D deficiency.

The Study: The authors recruited children eight to 24 months of age who received physical examinations in an urban primary care setting. Patients were evaluated for skin pigmentation, nutritional intake, and breastfeeding history, and were tested for serum 25-hydroxyvitamin D level. Patients identified as vitamin D deficient were further evaluated for bony demineralization.

Results: Of 365 children, 146 (40 percent) had suboptimal vitamin D levels (30 ng per mL [74 nmol per L] or lower), of which 44 children (12.1 percent) were vitamin D deficient (20 ng per mL [50 nmol per L] or lower). Infants and toddlers were equally susceptible. Infants who were breastfed without supplementation were 10 times more likely to be vitamin D deficient compared with infants who were exclusively bottle-fed. Among toddlers, milk consumption significantly reduced the chance of vitamin D deficiency (odds ratio [OR] = 0.51), with each cup of milk per day increasing serum 25-hydroxyvitamin D levels by 3.1 ng per mL (8 nmol per L). No correlation was found between vitamin D deficiency and sex, time spent outdoors, sunscreen use, sun sensitivity, or skin pigmentation.

Forty of the 44 children with vitamin D deficiency were further evaluated, with 13 (32.5 percent) exhibiting bony demineralization, and three (7.5 percent) also demonstrating rachitic changes on wrist and knee radiography. One child subsequently displayed evidence of rickets on clinical examination.

Conclusion: The authors conclude that vitamin D deficiency is common among infants and toddlers, and is strongly associated with breastfeeding without supplementation among infants. These findings support current recommendations for vitamin D supplementation for all young children, and the authors recommend that this be emphasized for all breastfed infants for the duration of breastfeeding.

editor's note: Vitamin D deficiency had been virtually eliminated in the United States by the 1950s because of sunlight exposure and fortifying milk with vitamin D. Recently, however, reports of vitamin D deficiency and rickets among U.S. children have been increasing. A clinical review in the same journal concluded that subclinical vitamin D deficiency is widespread among children of all ages and ethnicities, with potential long-term effects on bone health and the development of several chronic diseases.¹ Considering that the American Academy of Dermatology recommends that vitamin D be gained solely from diet rather than sunlight,² this will undoubtedly become a more pressing clinical issue.

Although vitamin D deficiency is recognized as a problem, there is much discussion as to what constitutes “good” levels of vitamin D. One review found improved clinical outcomes with vitamin D levels of 36 to 40 ng per mL (90 to 100 nmol per L).³ To achieve this, most adults would require more vitamin D (at least 700 to 1,000 IU per day) than allowed for by current recommendations. The current vitamin D recommendation for U.S. children is 200 IU per day, although 400 IU per day has been demonstrated to be safe in this group. The Canadian Paediatric Society recommends that all infants receive 400 IU per day of vitamin D,⁴ and the American Academy of Pediatrics has a similar recommendation.⁵ Serum 25-hydroxyvitamin D level is the best indicator of actual vitamin D status because it reflects dietary intake and synthesis from skin, and has a half-life of about 15 days.—k.t.m.