Experts discuss DRIs, with vitamin D changes getting strong support

By Stephen Daniells

- Last updated on GMT

Related tags: Vitamin, Nutrition, Vitamins

The upper limit (UL) of vitamin D should be raised to 250
micrograms per day, the Institute of Medicine heard last week, as
experts discussed the state-of-play of DRIs and ULs.

The nutrient has been linked to health benefits ranging from reduced risk of osteoporosis and fractures, to lower incidences of certain types of cancer. Coupled with the absence of adverse effects at higher doses, and with many experts advocating supplements as the safest and most consistent source of the vitamin, this could lead to a sales boost for the vitamin.

Experts from government, academia, and industry met in Washington last week for the Dietary Reference Intake Research Synthesis Workshop to discuss issues related to gaps in knowledge and the research that needs to be done to develop and advance the DRIs of all categories of nutrients.

John Hathcock, PhD, vice president of scientific & international affairs at the Council for Responsible Nutrition (CRN), told that there is always a need to review and revise recommended levels due to progress in research and understanding. This progress resulted in the strongest calls for an update for vitamin D.

"The current UL [50 micrograms] is based on a single clinical trial that reported adverse effects for 95 micrograms. This has been superceded by new clinical trials that have not reported any adverse effects at higher doses,"​ explained Dr Hathcock.

Hathcock, along with other prominent, independent experts, is calling for the UL to be raised to 250 micrograms per day, equivalent to 10,000 International Units (IU).

Such calls are in-line with other academics who have been calling for an increase in the dietary recommended intake (DRI) of the vitamin from its current level of 10 micrograms (400 IU) per day to 25 or even 50 micrograms per day.

Dr Hathcock gave a presentation at the workshop entitled, "DRIs for vitamin C, vitamin E, selenium and carotenoids,"​ and took time to consider the adverse effects associated with vitamin E intake that have been well-publicized in the media.

Special mention was made to the Miller meta-analysis, published at the start of 2005 in the Annals of Internal Medicine​ (Vol. 142, pp. 37-46), the methodology of which has been heavily questioned. Paraphrasing prominent statistician, Donald Berry, Hathcock said that the statistical method of Miller seemed to be designed to give a significant result.

A review of the literature led Dr Hathcock to conclude that the three major hypotheses relating to adverse effects from the vitamin (enhanced tendency to bleed, hemorrhagic stroke, and "all-cause mortality") were not valid.

Both extrapolated animal data and human data have led to the UL for vitamin E being set at 1000 mg per day. This figure is valid and no calls for changes were made.

The research needs to fill in the gaps for vitamin E, said Dr Hathcock, were for a statistical evaluation of multiple endpoints and trials, and an evaluation of the risks/benefits for gamma-tocopherol, compared to alpha-tocopherol.

He also noted that nutrients such as lutein, lycopene and some B vitamins have no set UL. Such an absence, he said, creates a "policy vacuum"​.

All categories of nutrients were discussed at the two-day workshop with the official report from the IoM expected to be published by the end of September.

DRIs will also be the subject of discussion at the up-coming CRN Day of Science, to be held July 25th.

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