Elsevier

The Journal of Nutrition

Volume 135, Issue 2, February 2005, Pages 317-322
The Journal of Nutrition

Symposium: Vitamin D Insufficiency: A Significant Risk Factor in Chronic Diseases and Potential Disease-Specific Biomarkers of Vitamin D Sufficiency
Circulating 25-Hydroxyvitamin D Levels Indicative of Vitamin D Sufficiency: Implications for Establishing a New Effective Dietary Intake Recommendation for Vitamin D1

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ABSTRACT

It has been more than 3 decades since the first assay assessing circulating 25-hydroxyvitamin D [25(OH)D] in human subjects was performed and led to the definition of “normal” nutritional vitamin D status, i.e., vitamin D sufficiency. Sampling human subjects, who appear to be free from disease, and assessing “normal” circulating 25(OH)D levels based on a Gaussian distribution of these values is now considered to be a grossly inaccurate method of identifying the normal range. Several factors contribute to the inaccuracy of this approach, including race, lifestyle habits, sunscreen usage, age, latitude, and inappropriately low dietary intake recommendations for vitamin D. The current adult recommendations for vitamin D, 200–600 IU/d, are very inadequate when one considers that a 10–15 min whole-body exposure to peak summer sun will generate and release up to 20,000 IU vitamin D-3 into the circulation. We are now able to better identify sufficient circulating 25(OH)D levels through the use of specific biomarkers that appropriately increase or decrease with changes in 25(OH)D levels; these include intact parathyroid hormone, calcium absorption, and bone mineral density. Using these functional indicators, several studies have more accurately defined vitamin D deficiency as circulating levels of 25(OH)D ≤ 80 nmol or 32 μg/L. Recent studies reveal that current dietary recommendations for adults are not sufficient to maintain circulating 25(OH)D levels at or above this level, especially in pregnancy and lactation.

KEY WORDS

vitamin D
25-hydroxyvitamin D
parathyroid hormone
vitamin D requirement
bone mineral density
calcium absorption

Abbreviations

7-DHC
7-dehydrocholesterol
25(OH)D
25-hydroxy- vitamin D
BMD
bone mineral density
DRI
dietary intake recommendation
MED
minimal erythemic dose
PTH
parathyroid hormone
UVB
UV blue

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1

Presented as part of the symposium “Vitamin D Insufficiency: A Significant Risk Factor in Chronic Diseases and Potential Disease-Specific Biomarkers of Vitamin D Sufficiency” given at the 2004 Experimental Biology meeting on April 18, 2004, Washington, DC. The symposium was sponsored by the American Society for Nutritional Sciences and supported in part by educational grants from the Centrum Foundation of Canada and The Coca-Cola Company. The proceedings are published as a supplement to The Journal of Nutrition. This supplement is the responsibility of the guest editors to whom the Editor of The Journal of Nutrition has delegated supervision of both technical conformity to the published regulations of The Journal of Nutrition and general oversight of the scientific merit of each article. The opinions expressed in this publication are those of the authors and are not attributable to the sponsors or the publisher, editor, or editorial board of The Journal of Nutrition. The guest editors for the symposium publication are Mona S. Calvo, Center for Food Safety and Applied Nutrition, U.S. Food and Drug Administration, Laurel, MD, and Susan J. Whiting, College of Pharmacy and Nutrition, University of Saskatchewan, SK, Canada.