Understanding the Dietary Reference Intakes (DRIs)
Both the Recommended Dietary Allowance (RDA) and Adequate Intake (AI) are part of a broader set of nutritional guidelines called the Dietary Reference Intakes (DRIs). The DRIs are a set of reference values developed for healthy people in the United States and Canada to plan and assess nutrient intakes. For details on the different reference values including EAR, RDA, AI, and UL, you can refer to {Link: NCBI https://www.ncbi.nlm.nih.gov/books/NBK45182/}.
The Direct Link: AI Replaces RDA When Evidence Lacks
The primary link between RDA and AI is their relationship within the DRI framework, where AI is used when there isn't enough evidence to establish an RDA. Setting an RDA requires sufficient data to first calculate an Estimated Average Requirement (EAR). If this data is lacking, an AI is developed instead, using different methods. The AI then serves as the recommended intake goal for individuals, acting as a substitute for the RDA when the scientific data is insufficient for a more precise calculation. This distinction is important; an AI indicates less conclusive data was available compared to an RDA. For example, AI is used for nutrients like vitamin K for infants, while an RDA exists for zinc for older infants due to more extensive data.
How Adequate Intake (AI) Values are Determined
Since AIs cannot be derived from an EAR, they are based on different data. Methods include observing nutrient intake in healthy populations or using experimental data. The AI for young infants, for instance, is based on the average nutrient intake from breast milk of healthy, breastfed infants. Other methods include experimental approximations, like the study used to set the AI for choline in adult men, and factorial estimates based on physiological factors, used for the AI for fluoride.
Key Differences Between RDA and AI
While both are individual intake goals, their basis and certainty differ.
| Feature | Recommended Dietary Allowance (RDA) | Adequate Intake (AI) |
|---|---|---|
| Basis of Derivation | Calculated from EAR to cover 97-98% of the population. | Based on observed intakes, experimental data, or approximations when EAR data is insufficient. |
| Strength of Evidence | Strong, statistically robust evidence. | Less conclusive scientific evidence. |
| Certainty of Adequacy | High certainty, covers 97–98% of healthy individuals. | Assumed adequate, but the percentage covered is unknown. |
| Use for Population Assessment | Not for assessing group inadequacy (EAR is used). | Cannot assess prevalence of inadequacy in a population. |
| Examples | Iron, zinc, vitamin C (most adults). | Vitamin K (infants), fiber, pantothenic acid. |
Practical Application of RDAs and AIs
For individuals, both RDA and AI serve as nutrient intake targets to help prevent inadequacy. However, AIs should be interpreted with more caution due to less certainty. Falling below an AI doesn't automatically mean inadequate intake but may warrant further assessment. For public health, the EAR is used for assessing group nutritional adequacy, while the AI is not suitable for this purpose because the distribution of requirements is unknown.
The Evolving Nature of Nutrition Science
Nutritional science is dynamic. As new research emerges, a nutrient with an AI might eventually have sufficient data to establish an EAR and subsequently an RDA. Expert panels periodically review and update DRIs based on new evidence. This ongoing process highlights the potential for AIs to be temporary and the continuous refinement of nutritional guidelines.
In conclusion, RDA and AI are linked through the strength of scientific evidence. AI is used as a recommended intake when robust data for an RDA is unavailable. Both are vital parts of the DRI system, guiding individuals toward adequate nutrient intake, although an RDA offers greater certainty due to its more rigorous derivation. For more information, consult resources from organizations like the National Academies Press or the National Institutes of Health.
