Evidence supports five-fold increase in level of daily intake deemed safe
During eons of evolution in tropical regions of Africa, humans adapted to their needs and environment by getting most of their vitamin D from sunlight, which stimulates creation of the hormone-like vitamin in skin cells.
The amounts of vitamin D generated when UV sunrays strike the skin are much higher than we can get from foods, reaching 20,000 International Units (IU) in about 20 minutes when the rays are strong, such as during summer in the temperate zone, or just about anytime in tropical regions.
With recent research affirming the ability of higher levels of vitamin D to prevent cancer and bone fractures—see “FDA Agrees” in our last issue—many experts have been calling for the US government to raise the recommended daily allowance (RDA) dramatically, from 400 IU to 1,000 IU or even 2,000 IU.
And credible estimates put the portion of vitamin-D-deficient people in northern temperate regions of the US and Europe, and China as high as 60 percent.
Given this documented problem and the rising tide of evidence that vitamin D is a critical anti-cancer and bone-building ally, it's been odd that US health authorities haven't rushed to raise the RDA.
One thing that's kept the RDA at the ineffectively low level of 400 IU is that the “tolerable upper intake level” (UL) in Europe and the US has been set at 2,000 IU (50 micrograms per day) for many years, despite the lack of any credible reason for such a low safety level.
Almost all of the cases of vitamin D toxicity reported to public health authorities have involved doses greater than the highest doses used in the clinical trials included in the review: huge amounts that the victims ingested for months.
In the US, the RDA and safe upper intake limit (UL) for vitamins are set by the Food and Nutrition Board of the US Institute of Medicine, which set the current upper intake limit for vitamin D almost ten years ago.
Current upper limit proven obsolete; higher intake aids bone health and can curb key cancers
As the authors of the new evidence review note in their introduction, a great deal of water has passed under the scientific bridge since the Food and Nutrition Board (FNB) set the current upper intake limit for vitamin D, in 1997:
“New data continue to emerge regarding the health benefits of vitamin D beyond its role in bone. The intakes associated with those benefits suggest a need for levels of supplementation, food fortification, or both that are higher than current levels” (Hathcock JN et al 2007).
The National Osteopososis Foundation estimates that about 55 percent of women over 50 are at risk, that 10 million have the disease already and that another 34 million have fragile bones.
Vitamin D facilitates calcium absorption in the intestine, making dietary calcium much more effective at building bone strength.
Yet, as Harvard researchers concluded in 2005, the current RDA (400 IU) is half what it needs to be to help prevent fractures: “Oral vitamin D supplementation between 700 to 800 IU/d [per day] appears to reduce the risk of hip and any non-vertebral fractures in ambulatory or institutionalized elderly persons. An oral vitamin D dose of 400 IU/d [per day] is not sufficient for fracture prevention” (Bischoff-Ferrari HA et al 2005).
And it's becoming clear that vitamin D is one of the body's most important defenses against common cancers: see “Higher Vitamin D Intake Could Cut Cancer Risk in Half.”
Last week, the researchers published the results of their evidence review, which should persuade the FNB members to raise the safety level, and may make them feel comfortable enough to raise the RDA.
The study's lead author, John Hathcock, Ph.D., is employed by the Council for Responsible Nutrition (CRN)—the lobbying and education arm of US supplement manufacturers, which funded the review—but his expert co-authors came from Mount Sinai Hospital in Toronto and Crieghton University in Nebraska.
And to ensure an apples to apples comparison, the authors used the same analytical methods the Food and Nutrition Board used to make their now-obsolete risk assessment in 1997.
What the new evidence review revealed
In addition to results from animal studies that used very high doses of vitamin D3—the natural, potent form found in salmon and other foods—the authors collected data from 21 clinical trials, in which researchers gave people doses of vitamin D3 ranging up to 2,500 micrograms, which is 50 times the current upper safety limit.
The authors found no evidence of toxicity in human clinical trials that used doses equal to or greater than 10,000 IU (250 micrograms) of vitamin D3 per day.
Accordingly, they believe that the evidence supports raising the safe upper limit for intake of vitamin D by a factor of five, from the current 2,000 IU per day to 10,000 IU per day.
The reviewers' conclusion was logical: “This demonstrated safety profile of vitamin D should safely permit increased intakes to achieve additional benefits of this vitamin at higher levels than previously recognized. Unfortified foods, fortified foods, and most dietary supplements, combined, do not contribute to a total exposure anywhere near the recommended vitamin D UL of 250 micrograms per day” (Hathcock JN et al 2007).
Let's hope that the Food and Nutrition Board takes the new, wholly scientific review and its authors' reasonable recommendations to heart.
And even if the Food and Nutrition Board does not, for some unscientific reason, raise the safety limit, it should at least raise the US RDA to ensure that Americans enjoy maximum protection from cancer and fractures.
- Hathcock JN, Shao A, Vieth R, Heaney R. Risk assessment for vitamin D. Am J Clin Nutr. 2007 Jan;85(1):6-18.
- Vieth R. Critique of the considerations for establishing the tolerable upper intake level for vitamin D: critical need for revision upwards. J Nutr. 2006 Apr;136(4):1117-22.
- Bischoff-Ferrari HA, Willett WC, Wong JB, Giovannucci E, Dietrich T, Dawson-Hughes B. Fracture prevention with vitamin D supplementation: a meta-analysis of randomized controlled trials. JAMA. 2005 May 11;293(18):2257-64. Review.