Re:Vit D level too good

[Guest guest]

Three recent papers on vitamin D:

1: Am J Clin Nutr.

2008 Jun;87(6):1952-8.

Vitamin D intake to attain a desired serum

25-hydroxyvitamin D concentration.

Aloia JF, Patel M, Dimaano R, Li-Ng M, Talwar SA, Mikhail M,

Pollack S, Yeh JK.

Bone Mineral Research Center,

Winthrop University Hospital,

Mineola, NY, USA.

BACKGROUND:

Indirect evidence suggests that optimal vitamin D status is

achieved with a serum 25-hydroxyvitamin D [25(OH)D]

concentration >75 nmol/L.

OBJECTIVE:

We aimed to determine the intake of vitamin D(3) needed

to raise serum 25(OH)D to >75 nmol/L.

DESIGN:

The design was a 6-mo, prospective, randomized,

double-blinded, double-dummy, placebo-controlled study

of vitamin D(3) supplementation. Serum 25(OH)D was

measured by radioimmunoassay. Vitamin D(3)

intake was adjusted every 2 mo by use of an algorithm

based on serum 25(OH)D concentration.

RESULTS:

A total of 138 subjects entered the study. After 2 dose

adjustments, almost all active subjects attained

concentrations of 25(OH)D >75 nmol/L, and no subjects

exceeded 220 nmol/L. The mean (+/-SD) slope at 9 wk

[defined as 25(OH)D change/baseline dose] was

0.66 +/- 0.35 (nmol/L)/(microg/d) and did not differ

statistically between blacks and whites. The mean daily

dose was 86 microg (3440 IU). The use of computer

simulations to obtain the most participants within

the range of 75-220 nmol/L predicted an optimal

daily dose of 115 microg/d (4600 IU). No hypercalcemia

or hypercalciuria was observed.

CONCLUSIONS:

Determination of the intake required to attain

serum 25(OH)D concentrations >75 nmol/L must consider

the wide variability in the dose-response

curve and basal 25(OH)D concentrations.

Projection of the dose-response curves

observed in this convenience sample onto the

population of the third National Health and Nutrition

Examination Survey suggests a dose of 95 microg/d

(3800 IU) for those above a 25(OH)D threshold of

55 nmol/L and a dose of 125 microg/d (5000

IU) for those below that threshold.

PMID: 18541590

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2. Nutr Rev. 2008 Oct;66(10 Suppl 2):S178-81.

Vitamin D: criteria for safety and efficacy.

Heaney RP.

Creighton University,

Omaha, Nebraska 68131, USA.

rheaney@...

The functional status indicator for vitamin D, for both

safety and efficacy, is serum 25-hydroxyvitamin D

concentration. Efficacy for several health endpoints

requires levels of 80 nmol/L or higher.

Toxicity occurs at levels of 500 nmol/L

or higher. The input needed for efficacy,

in addition to typical food and

cutaneous inputs, will usually be

1000-2000 IU/day of supplemental

cholecalciferol. Toxicity is associated

only with excessive supplemental intake

(usually well above 20,000 IU/day).

PMID: 18844846

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3. Estimation of the dietary requirement for vitamin D in healthy adults.

Cashman KD, Hill TR, Lucey AJ, N, Seamans KM, Muldowney S,

Fitzgerald AP, Flynn A, MS, Horigan G, Bonham MP, Duffy EM,

Strain J, Wallace JM, Kiely M.

Am J Clin Nutr. 2008 Dec;88(6):1535-1542.

<http://www.ajcn.org/cgi/content/abstract/88/6/1535>

estimates that the dietary intake requirement of vitamin D to ensure

maintenance of wintertime vitamin D status > 80 nmol/L, which most

vitamin D researchers nowadays seem to consider as a minimum lower limit

for optimal 25(OH)D range (some researches set the lower limit to 100

nmol/L or even higher), for the vast majority (>97.5%) of 20–40-year-old

healthy adults, is 41.1 µg/d (1644 IU/d).

PMID: 19064513

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