What if an individual has an intake above the UL on a chronic basis? For example, what if a person's magnesium intake from a nonprescribed antacid is 500 mg per day and the UL for magnesium (based on supplemental intake only) is 350 mg?
The most prudent advice in this situation would be to recommend that the individual reduce intake to below the UL. In this example, choosing a different type of antacid might be appropriate.
The consequences associated with nutrient excess—severity and reversibility of the adverse effect—vary for different nutrients. Moreover, little is known about nutrient-nutrient interactions at high doses. Without good evidence for an expected benefit, or unless under the supervision of a physician, there is no justification for intake above the UL.
If an individual decides to take a supplement for nontherapeutic purposes, should a supplement that contains the UL of a nutrient be selected?
No, supplements should not be chosen on this basis.
Use of a supplement containing the UL for a nutrient, when combined with intakes from foods, would place the individual at potential risk of adverse effects. Accordingly, a supplement which contains nutrients at levels below, or approximating the RDA or AI would be a more appropriate choice.
A test similar to the one described in the preceding section for the AI can be implemented to decide whether usual intake is below the UL given the observed mean intake. The test is constructed in exactly the same manner, but now the UL is subtracted from the mean observed intake for the individual. Again, this test cannot be used for nutrients with a large CV of daily intake such as vitamin A, vitamin B12, vitamin C, and vitamin E (see Appendix Table B-2 and Table B-3).
An example similar to the one presented in Table 3-2 is presented in Table 3-4. In the example, again the assessment is for a woman who is 40 years old. This woman has a normal activity pattern, energy intake not exceeding 2,500 kcal/day, and a mean phosphorous intake of 3.8 g (see IOM [1998b] for discussion of high phos-