| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
Letter to the Editor |
Council for Responsible Nutrition 1875 Eye Street, NW Suite 400 Washington, DC 20006-5409 E-mail: hathcock{at}crnusa.org
Dear Sir:
In their article on high doses of vitamin D, Vieth et al (1) provide data that are useful for evaluating vitamin D safety and interpreting the practical meaning of the tolerable upper intake level (UL) (2). The objectives, design, and data presentation of the study are straightforward and appropriate. Although the comments in the introduction and discussion sections are generally appropriate, they warrant additional explanation to clarify and correct certain interpretations in the hope that the policy implications of their data will be fully appreciated.
Vieth et al state that "Food and Nutrition Board guidelines specify 50 µg/d as the highest vitamin D intake that healthy adults can consume without risking hypercalcemia [it is the upper limit, or the no adverse effect level (NOAEL)]." This statement is wrong in specific ways that should be corrected.
The Food and Nutrition Board (FNB) identifies 50 µg/d as the UL for vitamin D for most healthy adults (3). The UL is defined as "the maximum level of total chronic daily intake of a nutrient judged to be likely to pose no risk of adverse health effects to the most sensitive members of the healthy population" (2). The UL is derived by dividing the NOAEL by an uncertainty factor that is identified from a specific database. For vitamin D, the FNB applied an uncertainty factor of 1.2 to an NOAEL of 60 µg/d to calculate the UL as 50 µg/d. The UL is equal to the NOAEL only if the uncertainty factor selected is 1.0. Therefore, for vitamin D the UL is not equal to the NOAEL.
The FNB' phrase "likely to pose no risk" is important. It does not mean that exceeding the UL by any amount will pose a risk. It correctly implies that the UL is an intake that should provide a comfortable margin of safety below the intakes that may cause adverse effects.
Vieth et al correctly state that the FNB identified 95 µg vitamin D/d as the lowest observed adverse effect level on the basis of data provided by Narang et al (4). The FNB characterized the severity of the adverse effect (hypercalcemia) observed by Narang et al at a vitamin D intake of 95 µg/d as "modest"; therefore, it is not surprising that the data from Vieth et al failed to show the modest adverse effect.
The modest adverse effects found by Narang et al at a vitamin D intake of 95 µg/d and the absence of adverse effects found by Vieth et al at a vitamin D intake of 100 µg/d indicate that the FNB' UL of 50 µg vitamin D/d provides a substantial margin of safety below the intakes that might cause vitamin D toxicity in most healthy adults. The only policy implication of the data by Vieth et al is that the FNB may wish to consider revising and increasing the UL for vitamin D.
REFERENCES
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
