The Family of Reference Values
When you see a '% Daily Value' on a label or a recommended intake in an article, it traces back to a set of reference figures called the Dietary Reference Intakes (DRIs), set by expert committees and summarized by the NIH Office of Dietary Supplements [1]. Four terms do most of the work:
| Term | What it means |
|---|---|
| **EAR** (Estimated Average Requirement) | The intake estimated to meet the needs of 50% of healthy people |
| **RDA** (Recommended Dietary Allowance) | The intake sufficient for nearly all (97–98%) healthy people |
| **AI** (Adequate Intake) | Used when there isn't enough evidence to set an RDA; a level assumed to be adequate |
| **UL** (Tolerable Upper Intake Level) | The highest daily intake unlikely to cause harm |
RDA vs AI
Both are 'aim for about this much' targets. The difference is confidence: an RDA is calculated from solid data on requirements, while an AI is the best estimate when that data is thin. Neither is a minimum you must hit every single day — they're averages over time.
The UL: Where 'More' Becomes Risky
The UL is a ceiling, not a goal. Above it, the risk of side effects climbs. This matters most for nutrients that build up in the body, like the fat-soluble vitamins (A, D, E, K) and minerals such as iron. Megadoses sold as 'high potency' can push past the UL — more is not automatically better, and for some nutrients it can be harmful.
A Crucial Caveat: Intake Is Not a 'Dose That Works'
The RDA and AI describe the intake needed to *avoid deficiency* in healthy people. They are not claims that a nutrient improves any specific condition, and they are not the same as the dose used in a clinical study. A trial might test far more — or less — than the RDA. So 'meets 100% of the Daily Value' tells you about adequacy and labeling, not about whether a supplement will do something for you.
How to Use These Numbers
- Treat the RDA or AI as a sensible target for general nutrition.
- Treat the UL as a safety ceiling, especially for fat-soluble vitamins and minerals.
- Don't assume a study dose equals the RDA, and don't assume 'more' is better.
- For personalized targets — pregnancy, kidney disease, malabsorption, or a diagnosed deficiency — work with a clinician.