Blood levels were barely adequate even in kids consuming 4 times as much vitamin D as the US RDA
by Craig Weatherby
The results of two clinical trials confirm that "high" doses of vitamin D are safe and that doses four times greater than the US RDA are barely adequate to maintain minimally healthful levels.
The new findings support the flood of research linking higher vitamin D levels—whether from sun exposure, supplements, or fatty fish—to reduced rates of a wise range of disease conditions.
RDA falls short of real needs
To put the high doses tested in the new studies in context, these are the current US recommended daily allowance (RDA) figures for vitamin D:
- Birth to age 50—200 IU/day (1,400 IU/week)
- Age 51-70—400 IU/day (2,800 IU/week)
- Age 71-plus—600 IU/day (4,200 IU per week)
However, most researchers now believe that the RDAs for adolescents (200 IU) and adults (400 IU) should be five to 10 times higher… that is, at least 1,000 or 2,000 IUs per day (i.e., 7,000 to 14,000 IUs per week).
Researchers at the American University of Beirut-Medical Center, Lebanon conducted two placebo-controlled clinical trials in children aged 10 to 17.
Both trials were designed to assess two things:
- The safety of relatively high doses of vitamin D;
- The effect of various vitamin D intakes on vitamin D blood levels.
They gave children various doses of vitamin D at various intervals, and measured the impact that vitamin D supplements had on kids' blood levels of the hormone-like nutrient.
Clinical trials affirm safety of desirably higher vitamin D intake by kids
The Lebanon-based team conducted two trials.
In a short-term study, 25 students (15 boys and 10 girls) took 14,000 IUs of vitamin D once a week for eight weeks, and their blood levels were monitored for an additional eight weeks.
This trial was conducted during the summer and early fall, when sun exposure produces the highest average levels of vitamin D.
In a long-term, one-year study, 340 students (172 boys and 168 girls) received either a low dose of vitamin D (1,400 IUs per week) or a high dose (14,000 IUs per week).
They measured the children’s blood levels of vitamin D (in nanograms per milliliter or ng/mL).
To put these doses in context, see our sidebar at page right, titled "RDA falls short of real needs".
Results indicate value of even higher intake levels
None of the children in either trial showed any adverse signs of vitamin D toxicity.
Fish fit the vitamin D bill; Sockeye salmon stand out
Certain fish rank among the very few substantial food sources of vitamin D, far outranking milk and other D-fortified foods.
Among fish, wild Sockeye Salmon may be the richest source of all, with a single 3.5 ounce serving surpassing the US RDA of 400 IU by about 70 percent:
Vitamin D per 3.5 ounce serving*
Sockeye Salmon—687 IU
Albacore Tuna—544 IU
Silver Salmon—430 IU
King Salmon—236 IU
*For our full test results, click here.
And only children given the equivalent of 2,000 IUs a day of vitamin D (1,400 IU per week) increased their blood levels from inadequate (about 15 ng/mL) to the level considered minimally adequate for adults (about 35 ng/mL).
As noted in our accompanying article (see “Vitamin D May Reduce Heart Attack Risk”), a team of expert vitamin D researchers concluded two years ago that optimal adult health requires a minimum vitamin D blood level of about 90 ng/mL, or three times the level (30 ng/mL) considered minimally adequate in adults (Bischoff-Ferrari HA et al. 2006).
Doctors remain unsure how much vitamin D children and adolescents need in their blood.
But children and adolescents are more likely to be vitamin D deficient, and are far less likely to reach vitamin D levels considered toxic, because their rapid skeletal growth requires vitamin D to regulate bone calcium levels.
As lead author Ghada El-Haff Fuleihan, M.D. said, “Our research reveals that vitamin D, at doses equivalent to 2,000 IUs a day, is not only safe for adolescents, but it is actually necessary for achieving desirable vitamin D levels. This is particularly relevant in light of the increasingly recognized health benefits of vitamin D for adults and children.”
- Bischoff-Ferrari HA, Giovannucci E, Willett WC, Dietrich T, Dawson-Hughes B. Estimation of optimal serum concentrations of 25-hydroxyvitamin D for multiple health outcomes. Am J Clin Nutr. 2006 Jul;84(1):18-28. Review. Erratum in: Am J Clin Nutr. 2006 Nov;84(5):1253. dosage error in abstract. Am J Clin Nutr. 2007 Sep;86(3):809.
- Duhamel JF, Zeghoud F, Sempé M, Boudailliez B, Odièvre M, Laurans M, Garabédian M, Mallet E. [Prevention of vitamin D deficiency in adolescents and pre-adolescents. An interventional multicenter study on the biological effect of repeated doses of 100,000 IU of vitamin D3] Arch Pediatr. 2000 Feb;7(2):148-53. French.
- Maalouf J, Nabulsi M, Vieth R, Kimball S, El-Rassi R, Mahfoud Z, El-Hajj Fuleihan G. Short-term and long-term safety of weekly high-dose Vitamin D3 supplementation in school children. J Clin Endocrinol Metab. 2008 Apr 29. [Epub ahead of print]
- Vieth R, Chan PC, MacFarlane GD. Efficacy and safety of vitamin D3 intake exceeding the lowest observed adverse effect level. Am J Clin Nutr. 2001 Feb;73(2):288-94.
- Wagner CL, Hulsey TC, Fanning D, Ebeling M, Hollis BW. High-dose vitamin D3 supplementation in a cohort of breastfeeding mothers and their infants: a 6-month follow-up pilot study. Breastfeed Med. 2006 Summer;1(2):59-70.