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Vitamin D and Iodine
Heaney
Risk assessment for vitamin D.
Hathcock JN, Shao A, Vieth R, Heaney R.
Am J Clin Nutr. 2007 Jan;85(1):6-18. Review.
"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 microg, 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 > or = 250 microg/d (10,000 IU vitamin D3) supports the confident selection of this value as the UL."
Barriers to optimizing vitamin D3 intake for the elderly.
Heaney RP.
J Nutr. 2006 Apr;136(4):1123-5.
"Available data on metabolic utilization of vitamin D3 indicate a total daily requirement of approximately 4000 international units (iu) (100 microg) or twice the current tolerable upper intake level (UL). In young individuals, most of this comes from the skin. However, cutaneous vitamin D3 synthesis declines with age, creating a need for increasing oral intake to maintain optimal serum 25-hydroxyvitamin D [25(OH)D] concentrations. Estimates of the population distribution of serum 25(OH)D values, coupled with available dose-response data, indicate that it would require input of an additional 2600 iu/d (65 microg/d) of oral vitamin D3 to ensure that 97.5% of older women have 25(OH)D values at or above desirable levels. The age-related decline in cutaneous input, taken together with the UL, creates a substantial barrier to the deployment of public health strategies to optimize vitamin D status in the elderly."