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Title:   Author  item
                                            WHITING, SUSAN - UNIV. SASKATCHEWAN, NUTR.item
                                            CALVO, MONA - CNT. FOOD SAFETY, FDAitem
                                            Stephensen, Charles
  Submitted to: Book Chapter
                                    Publication Type: Book / Chapter
                                    Publication Acceptance Date: 2/1/2008
                                    Publication  Date: 3/1/2008
                                    Citation: Whiting, S.J., Calvo, M.S., Stephensen, C.B. 2008. Current Understanding of Vitamin D Metabolism, Nutritional Status, and Role in Disease Prevention. Book Chapter. ISBN-13:978-0-12-374118-9, publ.date March 2008, Chapter 43:807-832.Interpretive Summary:
                                Technical Abstract: INTRODUCTION:
Vitamin D is a nutrient that, until recently, was neglected
by the nutrition community. Although it was recognized
in the early twentieth century as an essential nutrient,
recommendations for intake were often qualified as
being needed only in absence of sunlight. In theory (and
in ancient times when early humans all lived closer to the
equator), all vitamin D needs could be met by exposure to
sunlight that provided ultraviolet (UV)B radiation, but
only recently have we come to understand how UVB
acts and what other factors—particularly environmental—
mitigate cutaneous vitamin D synthesis. Studying
vitamin D requirements is difficult. Previous dietary
recommendations for vitamin D, such as the 1989 Recommended
Dietary Allowance [1], indicated a ‘‘relative paucity
of recent controlled studies [and] . . . lack of data’’ on
which to base requirements. It further stated that ‘‘[c]linical
osteomalacia appears to be rare in the United States.’’
What is known today, however, is that vitamin D
deficiency and insufficiency are more widespread [2]
than imaged even a decade ago when the Dietary Reference
Intakes (DRIs) were first published for vitamin D
[3]. What has occurred in the past 10 years is a new
understanding of vitamin D’s roles in the body, especially
for functions unrelated to calcium absorption, which has
been the long-standing primary recognized function of
vitamin D [4–7].
The role of vitamin D in preventing rickets was discovered
early in the nineteenth century, but it was not until the
1970s that the sequence of steps from skin precursors to
active metabolite was understood. Despite the interest generated
in solving the puzzle of how vitamin D increased
intestinal calcium absorption, there were several reasons
why progress toward a better understanding of vitamin D
requirements was not made. There were technical challenges
in analyzing vitamin D and its metabolites. There
was, beginning in the 1980s, a greater focus on dietary
calcium as the major ‘‘bone’’ nutrient, leaving vitamin D
with only a minor role in osteoporosis research. And finally,
the important contribution of sun exposure to vitamin D
status was not fully realized until recently. Indeed, estimations
for dietary recommendations in the complete yearround
absence of sun exposure give values that are 5 to 8
times higher than what is needed to maintain vitamin D
status through the winter. It has been shown that globally
there is greater prevalence of chronic diseases such as
cancer and immune disorders at extremes of latitudes
where sun exposure for skin synthesis of vitamin D is
limited [4].
Vitamin D affects people starting with fetal development
and continuing to old age, functioning at both the genomic
and nongenomic level in the regulation of key protein
synthesis or in the intracellular metabolic pathways in
virtually all tissues [5–7]. Growth, development, and
The opinions expressed in this chapter are those of the authors and do
not reflect those of the U.S. Food and Drug Administration.
Font: Times and FrizQuadrata Size:10/12pt Margins:Top:3pc Gutter:5pc T.Area:42pc_54pc6.6 1 Color Lines: 55 Chap. Open: Fresh Recto
Els US HAYA Ch43-P374118 18-12-2007 Page: 801 22:4 Trim:8.5in_11in Floats: Top or Bottom TS: Integra, India
Nutrition in the Prevention and Treatment of Disease, 2 Ed.
Copyright 2008, Elsevier, Inc.
All rights of reproduction in any form reserved. 801
maintenance of health are all affected, and in many regards,
quality of life is as well. This chapter, although acknowledging
vitamin D’s contribution through the lifespan,
focuses on vitamin D needs for maintenance of health,
and on vitamin D’s specific actions in selected clinical
conditions. Because research is ongoing, the reader can
expect to learn enough about vitamin D’s roles to be able
to understand and apply the research as it unfolds.


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