by Craig Weatherby
At the end of 2008, the U.S. and Canadian governments announced a joint review of vitamin D needs, which may lead to higher recommended daily intakes.
The review, which is to be conducted by the U.S. Institute of Medicine (IOM), will involve an examination of all available science to date.
|How much “D” is needed and safe?|
Most experts recommend taking at least 1,000 IU via food and supplements, and prefer an intake of 2,000 IU to 4,000 IU per day ... unless most of your skin is exposed to 20 to 30 minutes of strong sunlight per day.
Vitamin D experts recommend minimum blood levels ranging from 90 to 120 nanomoles per liter (nmol/L), which is the same as 36 to 48 nanograms per milliliter (ng/mL).
However, the average blood level in the U.S. is a subpar 24 ng/mL, and less than one in four Americans have healthy levels of 30 ng/mL or higher (Ginde AA et al. 2009).
Leading vitamin D researcher Ronald Vieth, M.D., reports that normal human blood levels of vitamin D extend above 200 nmol/L or 80 ng/mL (Vieth R 2004).
Dr. Vieth notes that sunshine can provide an adult with an amount of vitamin D equivalent to daily oral consumption of 10,000 IU, that clinical studies prove it is safe to take 10,000 IU per day, and that doses five times the current safe upper intake limit (2,000 IU) are often necessary for sun-deprived adults to maintain optimal blood levels (Vieth R 2007).
The researchers measured the participants’ blood levels of vitamin D, and the results, while not surprising, affirm researchers’ calls to urgently raise the RDI.
Among the 86 women who completed the study, those receiving the daily vitamin D supplements showed blood levels of vitamin D more than three times higher than the levels in the placebo group (35.3 nanomoles per liter, versus only 10.9 nanomoles per liter).
And 80 percent of the women who took vitamin D3 achieved vitamin D blood levels considered optimal by the Maine team, which they places at 75 nmol/L or more.
This outcome indicates that taking 800 IU per day may be adequate to optimize wintertime vitamin D status among most young women (or men) living in northern latitudes.
Yet the current U.S. RDI for adult women age 50 or under is only 200 IU.
Before you assume that vitamin D shortages are limited to northern latitudes be aware that studies routinely find shortages in sunny countries as well, due to indoor lifestyles and to clothes that cover most of the body.
Vitamin D recommendations versus needs: An overview
Current RDIs for vitamin D are 200 IU for people up to 50 years of age, 400 IU for people between 51 and 70, and 600 IU for folks over 70.
Most researchers believe the evidence supports an RDI of at least 1,000 IU for all ages, and higher for people in northern latitudes (Vieth R 2004).
Currently, the official safe upper intake limit is 2,000 IU per day, but numerous clinical studies show that it is safe for adults to take up to 10,000 IU per day... an intake level 50 times the current RDA for people aged 50 or less (200 IU).
Providing further assurance of the safety and efficacy of high vitamin D intakes, a recent study in sunny Lebanon found no adverse effects in adolescents who took 2000 IU of vitamin D3 per day for a year... an intake that merely raised their vitamin D levels into the desirable range (Maalouf J et al. 2008).
For more on this, see “Answers to Vitamin D Questions from a Leading Physician,” “American Kids Found Deficient in Vitamin D,” and “Vitamin D Deters Diabetes and More: Northern Teens Deficient.”
Even the American Dermatology Association—whose misguided anti-sun campaigns have contributed to the vitamin D shortage documented in many studies—now agrees that people need much more vitamin D.
The available evidence persuades most researchers that, compared to the small number of dangerous melanoma-type skin cancers that sun exposure may cause, the vitamin D generated by the same sun exposure probably prevents many times more breast, colon, and other deadly cancers.
- Ginde AA, Liu MC, Camargo CA Jr. Demographic differences and trends of vitamin D insufficiency in the US population, 1988-2004. Arch Intern Med. 2009 Mar 23;169(6):626-32. DOI: 10.1001/archinternmed.2008.604
- Gozdzik A, Barta JL, Wu H, Wagner D, Cole DE, Vieth R, Whiting S, Parra EJ. Low wintertime vitamin D levels in a sample of healthy young adults of diverse ancestry living in the Toronto area: associations with vitamin D intake and skin pigmentation. BMC Public Health. 2008 Sep 26;8:336.
- Maalouf J, Nabulsi M, Vieth R, Kimball S, El-Rassi R, Mahfoud Z, El-Hajj Fuleihan G. Short- and long-term safety of weekly high-dose vitamin D3 supplementation in school children. J Clin Endocrinol Metab. 2008 Jul;93(7):2693-701. Epub 2008 Apr 29.
- Nelson ML, Blum JM, Hollis BW, Rosen C, Sullivan SS. Supplements of 20 microg/d cholecalciferol optimized serum 25-hydroxyvitamin D concentrations in 80% of premenopausal women in winter. J Nutr. 2009 Mar;139(3):540-6. Epub 2009 Jan 21.
- Vieth R. Vitamin D toxicity, policy, and science. J Bone Miner Res. 2007 Dec;22 Suppl 2:V64-8. Review.
- Vieth R. Why the optimal requirement for Vitamin D3 is probably much higher than what is officially recommended for adults. J Steroid Biochem Mol Biol. 2004 May;89-90(1-5):575-9. Review.