I was going to write an article this week about the difference between official, science-based, and government-set RDAs (Recommended Dietary Allowances) and the (once) often inaccurate DVs (Daily Values) set by the FDA and used on labels throughout the United States. I wrote about this topic in a book a few years back, and I found it ludicrous how misinformed you could become simply by looking at a label to understand how much of a given vitamin or mineral you need.
As I was doing some research on what’s changed, however, I discovered that within the last two years the rules on DVs have—at long last—been updated! Amazing! Thus, this article is no longer really about the difference between RDAs and DVs, but an exploration of what once was and what currently is. This means looking at the concept of RDAs, because in my opinion this is the starting point for really understanding how our need for the various micronutrients is assessed. Once that is understood, many questions are automatically answered!
First, though, a quick look back at how DVs used to obfuscate nutritional understanding via food labels.
The Daily Value: Now Accurate, Once Ridiculous
When I wrote a book on multivitamins
Compared to the 1968 RDAs, modern RDAs have mostly been changed to be lower; with a handful of exceptions, further research has shown our need for the essential vitamins and minerals to be less than originally expected. Practically speaking, this gave supplements an edge over food, because most foods don’t naturally contain 100% of any vitamin or mineral (and certainly not at the elevated, inaccurate standards). Foods, therefore, appeared to be only a poor source of many vitamins and minerals, while supplements could easily pack everything they needed into a single pill.
Here’s an example, using vitamin A. Previously, the DV for vitamin A was 5,000 IU, or to use the modern measure 1,500 micrograms RAE (retinol activity equivalents). Today, the DV is only 900 micrograms RAE, based on the 900 microgram RAE RDA for men (700 microgram RAE for women). A single average-sized carrot nets you around 500 micrograms RAE, which is over 50% of modern standard—but according to the old standard it was only 33%. As it turns out, it only takes two carrots a day to get all the vitamin A you need, not three!
Thankfully, this is no longer an issue, at least not for foods and supplements with updated labels (which they all should be soon). It’s much clearer how well food nourishes than it was a couple years back, and hopefully that helps with public understanding in regard to meeting nutritional needs with food alone. But before we can really be assured of that, there’s another layer to unpack—onto the RDA!
The Recommended Dietary Allowance: Exploring the Upper Limits of Need
In my experience, what the Recommended Dietary Allowance (RDA) really measures is often misunderstood. Some people think that it’s sort of a government-mandated minimum standard, the equivalent of getting a C- grade in a class. Others think (perhaps more accurately) that it’s the amount of a given nutrient most people need to thrive. Few people realize it’s a statistically determined figure to ensure that 97.5% of all people will have adequate nutrition, which means it’s more than most people actually need.
Yet that is exactly what the RDA actually is—a measure we use to say with statistical probability that yes, if you get this much of a nutrient you are almost certain to have met or exceeded your daily need. If you get this much, you will see no further benefit to adding more, and you will suffer no harm stemming from inadequacy.
We can’t start with an RDA, however; first an EAR, or “Estimated Average Requirement”, must be determined. EARs are set on a nutrient-by-nutrient basis using appropriate data, meaning that scientists examine…
- What we know a nutrient does—e.g., antioxidant activity, carbohydrate metabolism, red blood cell formation, etc.
- The consequences of inadequate intake—e.g., anemia, peripheral neuropathy, neural tube defects, etc.
- The amount necessary to prevent deficiency symptoms.
- The amount necessary to fully power all bodily needs.
- The amount correlated to better prevention of chronic disease (when relevant).
Using this data, an amount is determined that will meet all the above criteria for 50% of the population—the EAR. If we only had access to the EAR, then at most what we could say is that there’s a 50% chance your diet would be adequate, but that’s hardly compelling and so an extra statistical layer is added on to determine the RDA. The RDA is set to be two standard deviations above the EAR, which according to standard distribution will meet the needs of 97.5% of all people (95% of people who fall within two standard deviations above and below, and then the 2.5% of people whose needs are more than two standard deviations below normal). In the rare case where there isn’t enough data to determine a standard deviation in the usual way, a 10% modifier is used instead, meaning the RDA is 1.2x the EAR in those cases.
Now we know what the RDA measures, so let’s break it down a bit further. Imagine a group of 1,000 people assigned to eat the same diet for a day, a diet that was scientifically determined to provide exactly 900 micrograms RAE of vitamin A. Of the people in that group…
- 975 would meet or exceed their daily requirements.
- 25 would not meet their daily requirements.
- 23 would need an estimated 1,038 micrograms RAE.
- 2 would need an estimated 1,175 micrograms RAE.
So, for our test diet, 23 people would need more (if they ate this diet daily) and 2 people would need considerably more. Let’s look at the “meet and exceed” group more closely:
- 135 would need near-exactly the 900 micrograms RAE they received.
- 840 would need less.
- 340 would be fine with only around 763 micrograms RAE.
- 340 would be fine with 625 micrograms RAE.
- 135 would okay with 488 micrograms RAE.
- 23 would thrive on only 350 micrograms RAE.
- 2 would inexplicably do well with only 213 micrograms RAE.
Put another way, 84% of people need less than the RDA for any given nutrient, and 50% of people need considerably less.
Of course, this is simplified for clarity and the actual data probably isn’t neatly distributed along a bell curve, but the main point remains: the RDA is a safeguard against inadequate intake. Most people need less to be healthy, and provided your diet is healthy, it’s all but certain you won’t become deficient in any vitamin or mineral.
RDAs Are Not Only Meant to Prevent Deficiencies
It’s not uncommon to hear that RDAs are designed only to ensure no one suffers any overt deficiencies, but this couldn’t be further from the truth. EARs (which RDAs are based on, remember) are set according to a large number of factors of which the prevention of deficiency symptoms is only one. If you ever read through the pages of data for a given nutrient (here’s a link to the one on vitamin A), you’ll see instantly that they consider numerous factors and explicitly reject using any single factor as the sole determinant because any EAR based on that factor might not adequately cover a person’s other needs! Here’s an example from the vitamin A chapter about using a dark adaptation test for the EAR:
Nevertheless, this approach can be used to estimate the average requirement for vitamin A but without assurance of adequate tissue levels to meet nonvisual needs for vitamin A.
Here’s another quote, this time about plasma retinol concentration:
Because of the relatively insensitive relationship between plasma retinol concentration and liver vitamin A in the adequate range, and because of the potential for confounding factors to affect the level and interpretation of the concentration, it was not chosen as a primary status indicator for a population for estimating an average requirement for vitamin A.
There are other sections like this, as well, with the general idea being “this measure could be used to assess nutrient status, but without a guarantee that other aspects of health won’t suffer, and so is rejected”. Only measures that adequately assess all aspects of health are given final consideration.
In the end, the EAR for vitamin A was set based on the minimum acceptable level of liver vitamin A (where excess vitamin A is stored) and the amount typically lost in a day. Adequacy, therefore, isn’t tied to any single sign of deficiency, but rather to the amount of “extra” vitamin A a healthy person typically stores. Eating more vitamin A than you can store will not improve health because you cannot store more, and at any rate, won’t change the amount available to the organs that need it because blood levels are tightly controlled. The estimated average requirement is set.
We might also look at the difference between the average EAR and the average intake necessary to avoid overt deficiency symptoms. For example scurvy—the biggest sign of vitamin C deficiency—is effectively prevented with an intake of only 10 milligrams per day. Is the EAR for vitamin C 10 milligrams, then? Far from it, it’s actually 75 milligrams (for men; RDA 90 milligrams). Obviously nobody wants to bleed from the gums or suffer any of the other heinous effects of scurvy, but we also want to enjoy all the other benefits of adequate vitamin C intake, and the RDA helps us do that by considering more than just the outright deficiency when determining an EAR.
This isn’t to say that RDAs are perfect or that they’ll never need to be updated again; chances are they will need to be. Certainly, there’s plenty of argument about the current values as well, with many groups trying to change them based on their findings. What you don’t really see are major recommendations for change, though; no one is saying the RDA for vitamin C should be 1,000 milligrams per day, even if a few groups argue that maybe we’d be better off with 120 milligrams or to have the women’s RDA match the men’s. All of this data is being tracked and considered, and if enough evidence comes together it’s likely to change the RDA. In the meantime, we should be comfortable in the overall accuracy of our current RDAs, especially given what you just learned above!
RDAs Have Your Nutrient Bases Covered
I’m really glad the new DVs match our current RDAs, even if I get less of an article out of it. It was horrendously confusing to consumers to have the “Nutrition Facts” label be overtly incorrect. It’s my hope that the newer, usually much lower DVs fill people with confidence about the foods they’re eating, because really there’s no need for supplements to get your vitamins and minerals!
A bigger part of the problem, however, are the common misunderstandings the public has about the intention of RDAs. RDAs aren’t just a failsafe against scurvy and xerophthalmia; they’re designed to keep you at peak health micronutrition-wise (statistically speaking)!
For the vast majority of people, meeting the RDA means exceeding one’s needs, even if just slightly. I’m not saying you shouldn’t try to get the RDA, because you should—I’m just saying that you’re probably okay even if you sometimes fail.
In the coming weeks, I’m going to write more about vitamins and minerals—to fill in some of the gaps on this site. They’re not the most important topic sports nutrition-wise (as I mentioned at least a couple times in this article, they’re rarely an issue), but there are some key points to talk about with them, so we’ll cover those.
Got any questions about RDAs (or EARs or DVs)? Leave them in the comments!
