To the Editors:
I read with great interest the recent article in the Journal: “Recommended Vitamin D Intake and Management of Low Vitamin D Status in Adolescents: A Position Statement of the Society for Adolescent Health and Medicine” [
[1]
].Although I agree with the essence of the position statement and use vitamin D supplementation in appropriate clinical situations, clinicians should be aware that there are several caveats that need to be addressed.
Vitamin D has become a hot topic in the past 3–5 years, but a true understanding of the interpretation of vitamin D levels is still in its infancy.
The following list exemplifies the problematic issues:
- 1.Vitamin D levels are not to be interpreted in the same manner as electrolyte levels. Vitamin D must be viewed as more similar to other steroid hormones because it is also influenced by a binding protein—vitamin D binding protein (VDBP). Variations in VDBP have been well documented [2,3,4]. These differences influence the response to exogenous vitamin D.
- 2.What qualifies as a normal vitamin D level is still open to debate, especially in children and adolescents [[5]].
- 3.Large, randomized control studies in children and adolescents are lacking, especially longitudinally [[5]].
- 4.In studies of adults, the major end point for interpretation of results is fracture rate or osteoporosis rate. Similar end points are rarely described in studies of youth [[6]].
- 5.Rickets, an accepted marker of vitamin D deficiency, has been documented to occur at vitamin D levels that are considered normal [[7]].
- 6.In a study of 93 young adult Hawaiian sun worshipers not using sunscreen, 51% had vitamin D levels below 30 ng/mL (75 nmol/L), the minimal level considered to be adequate [[8]].
- 7.In a study of 58 obese adolescents (body mass index, >95% for age), 29% had vitamin D levels below 20 ng/mL (deficient) but none had elevated parathyroid hormone levels (a marker of inadequacy of vitamin D) and none had bone mineral densities that were deficient [[9]].
- 8.Genetic issues: Just as there are variations in VDBP, there are variations in the vitamin D receptor and genetic polymorphisms that relate to bone mineral density and osteoporosis. Studies indicate that variations in VDBP and vitamin D receptor have a role in susceptibility to rickets and bone disease [10,11].
- 9.Accuracy of measurement of 25(OH) vitamin D: There is no reference standard as yet, but chromatographic techniques such as high-performance liquid chromatography and liquid chromatography-tandem mass spectroscopy are superior to immunochemical and competitive protein-binding assays. Thus, any single number cutoff for “normal” is questionable [[12]].
- 10.Finally, recommendations regarding calcium intake were not mentioned. Adequate calcium intake is needed along with vitamin D to accomplish good bone health [[6]].
I urge the Society for Adolescent Health and Medicine to help develop a collaborative multicenter, randomized control study of vitamin D and calcium metabolism in normal adolescents on a longitudinal basis addressing the above issues. Only in this way can a better understanding of what is truly normal and when and how to intervene in growing adolescents be derived.
References
- Recommended vitamin D intake and management of low vitamin D status in adolescents: A position statement of the Society for Adolescent Health and Medicine.J Adolesc Health. 2013; 52: 801-803
- Vitamin D binding protein genotype and osteoporosis.Calcif Tissue Int. 2009; 85: 85-93
- Common genetic variants of the vitamin D binding protein (DBP) predict differences in response of serum 25-hydroxyvitamin D [25(OH)D] to vitamin D supplementation.Clin Biochem. 2009; 42: 1174-1177
- Genetic polymorphisms of the vitamin D binding protein and plasma concentrations of 25-hydroxyvitamin D in premenopausal women.Am J Clin Nutr. 2009; 89: 634-640
- Defining vitamin D deficiency in children: Beyond 25-OH vitamin D serum concentrations.Pediatrics. 2009; 124: 1471-1473
- Vitamin D deficiency in children and its management: Review of current knowledge and recommendations.Pediatrics. 2008; 122: 398-417
- Nutritional rickets with normal circulating 25-hydroxyvitamin D: A call for reexamining the role of dietary calcium intake in North American infants.J Clin Endocrinol Metab. 2003; 88: 3539-3545
- Low vitamin D status despite abundant sun exposure.J Clin Endocrinol Metab. 2007; 92: 2130-2135
- Relation of body fat indexes to vitamin D status and deficiency among obese adolescents.Am J Clin Nutr. 2009; 90: 459-467
- Vitamin D receptor polymorphisms and nutritional rickets in Nigerian children.J Bone Miner Res. 2000; 15: 2206-2210
- Vitamin D receptor gene Fok1 polymorphism predicts calcium absorption and bone mineral density in children.J Bone Miner Res. 1999; 14: 740-746
- 25-hydroxyvitamin D measurement, 2009: A review for clinicians.J Clin Densitom. 2009; 12: 417-427
Article info
Publication history
Published online: August 07, 2013
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Copyright
© 2013 Society for Adolescent Health and Medicine. Published by Elsevier Inc. All rights reserved.
