Estimation of the dietary requirement for vitamin D in healthy adults.
BACKGROUND
Knowledge gaps have contributed to considerable variation among international dietary recommendations for vitamin D.


OBJECTIVE
We aimed to establish the distribution of dietary vitamin D required to maintain serum 25-hydroxyvitamin D [25(OH)D] concentrations above several proposed cutoffs (ie, 25, 37.5, 50, and 80 nmol/L) during wintertime after adjustment for the effect of summer sunshine exposure and diet.


METHODS
A randomized, placebo-controlled, double-blind 22-wk intervention study was conducted in men and women aged 20-40 y (n = 238) by using different supplemental doses (0, 5, 10, and 15 microg/d) of vitamin D(3) throughout the winter. Serum 25(OH)D concentrations were measured by using enzyme-linked immunoassay at baseline (October 2006) and endpoint (March 2007).


RESULTS
There were clear dose-related increments (P < 0.0001) in serum 25(OH)D with increasing supplemental vitamin D(3). The slope of the relation between vitamin D intake and serum 25(OH)D was 1.96 nmol x L(-1) x microg(-1) intake. The vitamin D intake that maintained serum 25(OH)D concentrations of >25 nmol/L in 97.5% of the sample was 8.7 microg/d. This intake ranged from 7.2 microg/d in those who enjoyed sunshine exposure, 8.8 microg/d in those who sometimes had sun exposure, and 12.3 microg/d in those who avoided sunshine. Vitamin D intakes required to maintain serum 25(OH)D concentrations of >37.5, >50, and >80 nmol/L in 97.5% of the sample were 19.9, 28.0, and 41.1 microg/d, respectively.


CONCLUSIONS
The range of vitamin D intakes required to ensure maintenance of wintertime vitamin D status [as defined by incremental cutoffs of serum 25(OH)D] in the vast majority (>97.5%) of 20-40-y-old adults, considering a variety of sun exposure preferences, is between 7.2 and 41.1 microg/d.
Cashman
Kevin D
KD
Department of Food and Nutritional Sciences, University College, Cork, Ireland. k.cashman@ucc.ie
Hill
Tom R
TR
Lucey
Alice J
AJ
Taylor
Nicola
N
Seamans
Kelly M
KM
Muldowney
Siobhan
S
Fitzgerald
Anthony P
AP
Flynn
Albert
A
Barnes
Maria S
MS
Horigan
Geraldine
G
Bonham
Maxine P
MP
Duffy
Emeir M
EM
Strain
J J
JJ
Wallace
Julie M W
JM
Kiely
Mairead
M
D000328:Adult; D050071:Bone Density Conservation Agents / Q000008:administration & dosage* / Q000097:blood; D002762:Cholecalciferol / Q000008:administration & dosage; D019587:Dietary Supplements; D004305:Dose-Response Relationship, Drug; D004311:Double-Blind Method; D004797:Enzyme-Linked Immunosorbent Assay; D005260:Female; D006801:Humans; D008297:Male; D018673:Nutrition Policy; D009751:Nutritional Requirements; D012016:Reference Values; D012621:Seasons; D013472:Sunlight; D014466:Ultraviolet Rays; D014807:Vitamin D / Q000008:administration & dosage* / Q000031:analogs & derivatives* / Q000096:biosynthesis / Q000097:blood; D055815:Young Adult
D050071:Bone Density Conservation Agents; D014807:Vitamin D; D002762:Cholecalciferol; C104450:25-hydroxyvitamin D