Can you help explain how to read the vitamin A chart?

Q: I am confused about how to read the chart on Vitamin A in that nutrient’s article. In particular, it notes that carrots contain 686%DV. Does this mean that I only need to eat about 1/7th cup to get what I need of this nutrient?

A: Vitamin A is especially confusing when it comes to our daily requirement, and we’ve tried to simplify the information on our website in a way that could be expanded to include a great many more details.

The best individualized public health guidelines for nutrient intake are called the Dietary Reference Intakes, or DRIs. These guidelines are issued by the U.S. National Academy of Sciences’ Institute of Medicine (IOM), and they are revised every 10 years or so. The NAS has just finished going through a major revision of all the DRIs. The DRIs are good individual guidelines because they are different for all age groups, and they are different for men and women. We report these DRI recommendations in the Public Health Recommendations section of our nutrient articles. With respect to vitamin A, the DRI for adult women is 700 micrograms.

This recommendation of 700 micrograms of retinol seems simple, but it is not. Retinol is the active form of vitamin A. Very few of us get 700 micrograms of the active form from our food. Instead, we get a “preliminary” form of vitamin A that our body can convert into retinol. Beta-carotene, alpha-carotene, and beta-cryptoxanthin are all considered “preliminary” forms of vitamin A because our body can convert all of these forms into retinol. However, the amount of each form we need to get 1 microgram of retinol is different. In the case of beta-carotene, we need 12 micrograms to produce 1 microgram of retinol. In the case of alpha-carotene, we need 24 micrograms. We also need 24 micrograms when we convert beta-cryptoxanthin into retinol.

Fortunately, many foods contain these “preliminary” forms of vitamin A. Carrots, which you used in your example, contain all of these carotenoid forms. Most adults get the majority of their vitamin A from these preliminary carotenoid forms of vitamin A. But since there are different conversion factors used to determine how much of each carotenoid is needed, it’s difficult to arrive an anything better than a general estimate about the amount of food required to end up with 700 micrograms of retinol that have been converted inside the body from carotenoids.

One microgram of retinol converts into 3.33 International Units (or IUs) of vitamin A. For this reason, a 700-microgram requirement of retinol would translate into approximately 2,333 IU. However, the number of carotenoid IUs it would take to produce these 2,333 IU of vitamin A would vary in exactly the same way as the microgram conversion factors vary in the information we’ve described above.

When we established our website’s food rating system, we decided not to use any of the above guidelines. We believed that the many gender-specific and age-specific recommendations would get too confusing to website visitors. In addition, we wanted to offer recommendations that were in keeping with the nutrition information found on packaged food in the grocery store. For both of these reasons, we chose to use another set of recommendations, called Daily Values, as the basis for our food rating system. The Daily Values, or DVs, are not issued by the IOM, but rather by the U.S. Food and Drug Administration (FDA). These DVs are not specific to age, or to men and women. Instead, they are based on average needs and a single level of calorie intake (2,000 calories). The DVs are different from the DRIs. The DV for vitamin A is 5,000 IU. On our website, we take this 5,000 IU requirement and compare a food’s total IU to this amount. When we make our comparison, we consider all forms of vitamin A in a food, including retinol, beta-carotene, alpha-carotene, and beta-cryptoxanthin.

In the case of carrots, these different forms of vitamin A combine to produce a total of about 34,000 IU per cup of sliced fresh carrots. That amount is a little less than 7 times the Daily Value of 5,000 IU (7 times the Daily Value is the same as 700% DV). In our Nutrient Rating System Chart, this is approximately the number you see in the %DV column for 1 cup of carrots—we actually show 686.3% on our website, but that is very close to 700%. If you only wanted to get 100% DV, you would only need about 1/7th of a cup of sliced carrot.

Whether the DV amount (5,000 IU) is sufficient for your current personal vitamin A needs is a much different question. Your current state of health, health history, family history, and other factors are important in deciding the amount of vitamin A you need. In some cases, a healthcare practitioner might also want you to get a certain percent of your vitamin A in the active vitamin form (retinol). In other cases, more carotenoids are advisable. Many individuals require more than the DV amount to stay optimally healthy. However, in a website trying to present general nutrition information focused on food, we’ve tried to leave all of these clinical nutrition questions to our website visitors and their healthcare providers.

In the case of the carotenoids, going substantially over the Daily Value is not known to be a problem in the case of the preliminary carotenoid forms of vitamin A. The National Academy of Sciences has set Tolerable Upper Limits (or ULs) for the retinol form of vitamin A, however, and that UL is 3,000 micrograms (or 10,000 IU) for adult women. There is virtually no preformed retinol in carrots, however, and so this UL would not apply to carrots and the 34,000 IU found in one cup. In general, preformed retinol is only found in substantial amounts in animal (versus plant) foods.

As you can see, the complete picture for vitamin A and food is complicated! However, as long as you are talking about plant foods, and you are getting at least 100%DV from those foods, you are likely to be heading in a healthy direction.

In our rating system we calculated %DV in order to help people identify how much contribution the food would provide towards meeting a nutritional intake goal. Yet, the values set by the IOM for dietary goals vary by age and gender. Since we needed one number, the value we adopted as our standard for DVs was from the U.S. Food and Drug Administration’s “Reference Values for Nutrition Labeling.” These are the values used by food manufacturers in the “Food Facts” portion of their product’s label.

Therefore this value may be different than that which your individual nutrient needs require.

To best use the chart, then, you could see how much of a certain nutrient a food contained. Let’s use the carrot example. One cup of raw carrots contains 34,317 IU of Vitamin A. How does that compare to your nutrient intake goal?

What happens if it exceeds 100%? This answer depends upon numerous factors.

For example, if your nutrient intake goals are based upon a value described by a public policy group (for example the DRIs set by the IOM) then it is important to remember that these nutrient goals were created for a group, and don’t necessarily reflect your individual health needs. You may need more (or less). The only way to find that out is to consult with a licensed healthcare practitioner skilled in nutrition who can help you identify your individual nutrient needs based upon your health.

It also depends upon the nutrient. For some nutrients, ULs are set by public policy recommendations based upon them reviewing data from studies that suggest that after a certain level there can be negative side effects from too much of a nutrient. This is more likely to happen with dietary supplements but in some cases it may with foods. Yet, not every nutrient has an upper limit concern. For example, the carotenoids found in carrots which are converted into (and measured as) vitamin A have been found to be non-toxic and therefore there is no upper limit set for their dietary intake. Therefore, for example, if carrots contribute more than 100% of your dietary vitamin A daily requirements, since they do so because of their carotenoids, this is nothing to be concerned about and you can enjoy a cup rather than a smaller amount.

For more information on this topic, please see: Vitamin A Our Food and Recipe Rating System