take from supplements was 117 mg (4.9 mmol)/day, or approximately the UL (115 mg [4.8 mmol]/day) for a 6-year-old child weighing 23 kg. Assuming older children were taking the higher doses, it appears that about 5 percent of the users in this study were exceeding the UL.

Using data from 1986, almost 1 percent of all adults in the United States took a nonfood magnesium supplement that exceeded the reference UL of 350 mg (14.6 mmol)/day in the 2-week period preceding the survey (Moss et al., 1989). It is important to note that many of the individuals whose intakes of supplemental magnesium exceeded the UL may be self-selected as not experiencing diarrhea, but this is uncertain. More recent data on estimates of supplement intakes of a national sample have not been published, but it is unlikely that usage has declined.

The data on supplement use in 1986 also indicate that at least 5 percent of young children who used magnesium supplements exceeded the UL for magnesium, 5 mg (0.2 mmol)/kg/day. However, because less than 10 percent of the children had taken a magnesium supplement in the past 2 weeks, less than 1 percent of all children would be at risk of adverse effects. These estimates assume that older children (with a higher UL) are taking the higher doses; the percentage at risk would be higher if dosage were not related to age (and, therefore, to body size). More information on supplement use by specific ages is needed.

The ability to determine reference dietary intakes for magnesium is, as indicated throughout this chapter, hampered by available data. Areas of investigation that are particularly needed include the following:

• Reliable data on population intakes of magnesium are required based on dietary surveys that include estimates of intakes from food, water, and supplements in healthy populations in all life stages.

• Biochemical indicators that provide an accurate and specific marker(s) of magnesium status must be investigated in order to assess their ability to predict functional outcomes that indicate adequate magnesium status over prolonged periods.