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trolled trials and less to nonrandomized trials; prospective cohort, retrospective cohort, and case-control studies; case-series; and single-case reports. Publications solely expressing opinions were not used in setting DRIs.

Statistical association does not imply causation, and this is especially true for relationships between nutrient intake and developmental abnormalities or chronic disease risk reduction as well as for toxic effects. The criteria proposed by Hill (1971) were considered when examining the evidence that a relationship might be causal:

  • strength of the association, usually expressed as a relative risk or a correlation coefficient;

  • dose-response relationship;

  • temporally plausible association, with exposure preceding the effect;

  • consistency of association in time and place;

  • specificity of cause and effect; and

  • biological plausibility.

For example, biological plausibility would not be sufficient in the presence of a weak association and lack of evidence that exposure preceded the effect.

Data were examined to determine whether similar estimates of the requirement resulted from the use of different indicators and different types of studies. For a single nutrient the criterion for setting the Estimated Average Requirement (EAR) may differ from one life stage group to another because the critical function or the risk of disease may be different. When no or very poor data were available for a given life stage group, extrapolation was made from the EAR or Adequate Intake (AI) set for another group based on explicit assumptions on relative requirements.

Method to Determine the Adequate Intake for Infants

The AI for young infants is generally taken to be the average intake by full-term infants who are born to healthy, well-nourished mothers and who are exclusively fed human milk. The extent to which intake of a nutrient from human milk may exceed the actual requirements of infants is not known, and ethics of experimentation preclude testing the levels known to be potentially inadequate. Using the breastfed infant as a model is in keeping with the basis for earlier recommendations for intake (e.g., Health Canada, 1990; IOM, 1991). It also supports the recommendation that exclusive

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