individuals if they consume a nutrient in amounts exceeding the recommended intake (the RDA or AI).
The UL is based on an evaluation conducted by using the methodology for the risk assessment of nutrients. The need for ULs has arisen because high consumption levels of some nutrients have resulted from the increased nutrient fortification of conventional foods and the increasing use of dietary supplements. The UL applies to chronic daily use and is usually based on the total intake of a nutrient from food, water, and supplements if adverse effects have been associated with total intake. However, if adverse effects have been associated with intake from supplements or food fortificants only, the UL is based on nutrient intake from one or both of those sources only rather than on total intake. As in the case of applying AIs, professionals should avoid very rigid application of the ULs and should first assess the characteristics of the individual or group of concern (e.g., the source of nutrient, the physiological state of the individual, and the length of sustained high intakes).
For some nutrients data may not be sufficient to develop a UL. This indicates the need for caution in consuming amounts greater than the recommended intake; it does not mean that high intake poses no potential for risk of adverse effects.
The safety of routine, long-term intake above the UL is not well documented. Although the general population should be advised not to routinely exceed the UL, intake above the UL may be appropriate for investigation within well-controlled clinical trials. Clinical trials of doses above the UL should not be discouraged as long as participants have signed informed consent documents regarding possible toxicity and they are appropriately monitored. Because the DRI concept is relatively new, there are few published reports that have examined population-based intake levels in the context of the UL. Recent dietary intake studies, which take into account nutrients from conventional food and dietary supplements, have demonstrated total intake levels that regularly approach and sometimes exceed the ULs (Allen and Haskell, 2002; O’Brien et al., 2001). Long-term intake of nutrients at levels above the UL places individuals at risk for adverse effects, but only continued longitudinal research will be able to demonstrate the level of potential harm.
The life stage groups described below were chosen as part of the initial DRI process (IOM, 1997) while keeping in mind all the nutrients to be reviewed. If data were too sparse to distinguish differences