Microsoft word - faqs on vitamin d.docx

FAQs on Vitamin D
Q: How do you measure vitamin D? What is considered deficient?
A: Body stores of vitamin D are measured by blood levels of 25-hydroxy-vitamin D
(25(OH)-vitamin D). Levels over 30ng/ml are considered sufficient (but may require
maintenance doses of vitamin D to sustain these levels); 15-30ng/ml are considered
insufficient (and require supplementation); and under 15ng/ml is considered deficient (and also
require supplementation).
Q: Is nutritional (25-hydroxy Vitamin D) deficiency/insufficiency really a problem?
A: Worldwide, it is estimated that 1 billion people are vitamin D deficient or
insufficient1. In CKD, prevalence rates range from 70% to over 90% 2,3,4. Given the wide
variety of tissues that have vitamin D receptors and the potential health complications
linked to vitamin D, maintaining adequate vitamin D levels is an important part in the
overall care of people with CKD.
Q: I give my patients activated vitamin D (Rocaltrol, Hectorol, Zemplar, etc). Isn’t that
sufficient?
A: There are many tissues in the body that have their own 1-alpha hydroxylase that is
able to activate vitamin D. Nutritional vitamin D (like cholecalciferol) is required to
generate activated vitamin D which acts locally to produce tissue-specific effects.
Activated vitamin D when administered as a medication has a much shorter half life and
is present in much smaller amounts – insufficient to fuel the extra-renal 1-alpha
hydroxylase. This is reinforced in the KDOQI guidelines, which say “[c]alcitriol or
another 1a-hydroxylated vitamin D sterol should not be used to treat vitamin D
deficiency.”
Q: Is 1000IU daily really enough? I think you need more.
There is evidence that 800-1000 IU daily of cholecalciferol is sufficient to increase 25-
hydroxyvitamin D levels and to maintain those levels in CKD5 and ESRD6. In addition,
successful trials looking at outcomes such as fracture prevention and fall prevention (muscle
strength) also used doses of about 1000 IU/day ,78. If additional vitamin D is necessary, separate
supplementation can be given in addition to ProRenal® vitamins.
Q: Is it safe to give active Vitamin D and nutritional Vitamin D?
A: There are studies in patients with ESRD on hemodialysis showing that combined
treatment with low and high dose cholecalciferol with activated vitamin D (alphacalcidol
or calcitriol) was safe, with hypercalcemia occurring very rarely 9,10. However, continued
monitoring of calcium and phosphorus would be prudent to avoid complications.
Q: Why are you using cholecalciferol instead of ergocalciferol?
A: There is a substantial amount of evidence showing the superiority of cholecalciferol
over ergocalciferol. Cholecalciferol leads to greater rises in 25-hydroxy vitamin D
levels11 and maintains those levels better over time12. In addition, all successful fracture
prevention trials used cholecalciferol13. There are specific reasons why cholecalciferol
may be more efficacious, including higher affinities for the 25-hydroxylase enzyme,
higher affinity for vitamin D receptors and vitamin D binding proteins, and differences in
deactivation compared to ergocalciferol14. Because of these reasons, a number of experts
in the field of Vitamin D recommend using cholecalciferol over ergocalciferol 1,14.
References:
1 Holick M. N Engl J Med 2007;357:266
2 LaClair, R Am J Kidney Dis. 2005;45(6):1026
3 Ravani, P. Kidney International 2009; 75: 88
4 Saab, G. Nephron Clin Pract 2007;105:c132
5 Kooienga, L. Am J Kidney Dis 2009; 53(3):408
6 Jean, G. Nephrol Dial Transplant (2008) 23: 3670–3676
7 Chapuy, M. N Engl J Med 1992; 327:1637
8 Bischoff-Ferrari, H. Am J Clin Nutr 2006;84:18
9 Tokmak, F. Nephrol Dial Transplant (2008) 23: 4016–4020
10 Jean, G. Nephrol Dial Transplant (2008) 23: 3670–3676
11 Trang H, Am J Clin Nutr 1998;68:854
12 Armas LA. J Clin Endocrinol Metab 2004;89:5387–91
13 Bischoff-Ferrari HA. JAMA 2005;293:2257
14 Houghton, L. Am J Clin Nutr 2006;84:694

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