The tolerable upper intake level for oral vitamin D3 should be increased five-fold, experts from the US-based Council for Responsible Nutrition (CRN) have said after a review of the science.
The risk assessment provides companies with a guide for safe upper levels for product formulations, and consumers with vital information on safe dosage levels from products.
“This risk assessment was needed to show that newer evidence supports the conclusion that vitamin D is much safer then previously thought, particularly because of all the emergence research that shows benefit for vitamin D at higher levels than consumers were traditionally taking,” lead author John Hathcock said.
Currently, the tolerable upper intake level (UL) in Europe and the US is set at 2000 International Units (IU), equivalent to 50 micrograms per day. However, recent research, particularly from clinical trials, suggests that this should be raised. The CRN scientists state that this could be raised to 10,000 IU (250 micrograms per day).
The reviewers, from the CRN, Mount Sinai Hospital in Toronto and Crieghton University in Nebraska, pooled data from 21 clinical trials using doses ranging from 10 to 2500 micrograms (100,000 IU). The risk assessment also included data from animal studies, some of which used “extraordinarily high doses of vitamin D3”.
“The lack of adverse effects in clinical trials that used intake up to 1250 micrograms 50,000 IU vitamin D per day and the lack of adverse effects at lower doses inspires a high level of confidence in the data from the strongly designed clinical trials that used 250 micrograms 10,000 IU vitamin D per day,” said the reviewers.
The researchers also note that for practically all the reported cases of vitamin D toxicity have involved doses that were in excess of those studied in the clinical trials. “Newer clinical trial data are sufficient to show that vitamin D is not toxic at intakes much higher than previously considered unsafe,” said the reviewers.
Vitamin D is made by the body on exposure to sunshine, or can be consumed in small amounts in milk, fish, liver and egg yolk. However because of the low amounts present in the diet, and lack of sunshine in northern climates, with some estimates claiming that as much as 60 percent of northern populations may be vitamin D deficient.
The reviewers note that normal dietary sources provide about 2.5 micrograms per day, while this can be increased up to 10 micrograms with fortified foods. Dietary supplements would provide higher doses.
“We applied the same method to our risk assessment as the Food and Nutrition Board had used years ago, and our results concluded vitamin D could be safely taken in much higher amounts,” Hathcock said.
The objective of this review was to apply the risk assessment methodology used by the Food and Nutrition Board (FNB) to derive a revised safe Tolerable Upper Intake Level (UL) for vitamin D. 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. A prevailing concern exists, however, regarding the potential for toxicity related to excessive vitamin D intakes. The UL established by the FNB for vitamin D (50 µg, or 2000 IU) is not based on current evidence and is viewed by many as being too restrictive, thus curtailing research, commercial development, and optimization of nutritional policy. Human clinical trial data published subsequent to the establishment of the FNB vitamin D UL published in 1997 support a significantly higher UL. We present a risk assessment based on relevant, well-designed human clinical trials of vitamin D. Collectively, the absence of toxicity in trials conducted in healthy adults that used vitamin D dose 250 µg/d (10,000 IU vitamin D3) supports the confident selection of this value as the UL.
J.N. Hathcock, A. Shao, R. Vieth, R. Heaney. Risk assessment for vitamin D. American Journal of Clinical Nutrition; January 2007, Volume 85, Pages 6-18.