I tried one myself - putting in Vitamin C with an orange and then adding a supplement containing Vitamin C.
It seemed pretty complicated, the way all the stuff adds up!
I myself complicated it even more by using my Gummy Bear vites which are obviously for kids! The bottle's nutrition information says that 126 mg is 210% of the RDA, which is true if the RDA is 60 mg. But the RDA is broken down into gender and age.
See the definition of RDA (it mentions gender and age):
Dietary Reference Intake - Wikipedia, the free encyclopedia
The kids' vitamin that I take has 126 mg Vitamin C, which is reported as 210% RDA - aha, I read it as 'RDA' but in fact it is 'DV.'
210% is true if the RDA is 60 mg. But that's not an RDA for a child. I am using the 'per serving' value for the gummies.
What the bottle says is '% Daily Value 4& up.'
So, here's what Daily Value is:
Daily Values (DVs)
'Recommended intakes of nutrients vary by age and gender and are known as Recommended Dietary Allowances (RDAs) and Adequate Intakes (AIs). However, one value for each nutrient, known as the Daily Value (DV), is selected for the labels of dietary supplements and foods. A DV is often, but not always, similar to one's RDA or AI for that nutrient. DVs were developed by the U.S. Food and Drug Administration (FDA) to help consumers determine the level of various nutrients in a standard serving of food in relation to their approximate requirement for it. The label actually provides the %DV so that you can see how much (what percentage) a serving of the product contributes to reaching the DV'
Guidance for Industry: A Food Labeling Guide (14. Appendix F: Calculate the Percent Daily Value for the Appropriate Nutrients)
Sure enough, 60 mg shows up as the Vitamin C requirement for ages '4 and up.'
Using this one vitamin, C, as an example, 74.4 mg in an orange is using the nutritional information in a food database and this shows up correctly as 99% of 75.0, which is correct for my age group and gender.
But the gummy bears are reported as 126 mg and 210% DV (Daily Value). Combined, those percentages are 309%. Combined, those mgs. are 200.4 mg.
How to figure out the percentage when one is by sex and gender (Fitday knows your sex and gender, right?) and one is a huge group '4 and up'?
I think that's where the problem occurs.
My total, which is 74.4 mg (the orange) plus 126 mg (the supplement) is 200.4 mg. Fitday sees that as the total mg and then uses the 75 mg for my age and gender to figure the percentage, which is 267%. If you added the two percentages together that the supplement gives and the RDA database gives, you would have 99% + 210%, which is 309%. Higher. The two percentages should not be added together - they are percentages of different measurements.
The glitch, if there is any, is that fitday could ask you for the mg instead of the percentage (%RDA). I don't know the reasoning behind this, but it could be that labels cover a lot of territory - can you list something on a label without the mg and just give the RDA? Excuse me, I guess that would be DV.
People want to have that mg information interpreted, I'm sure - the FDA wants it to be shown in context, too. They have the DV: ' In order to limit consumer confusion, however, the label includes a single term (i.e., Daily Value (DV)), to designate both the DRVs and RDIs.' (from the text in the DV link given above...)
Does not limit consumer confusion, IMO. However, it is general enough to eliminate the gender and age thing - which the RDA takes into account (used by fitday).
But whatever the reasoning behind all the different designations, fitday is still going to use the measurement unit (mg, for example) and the RDA - as long as it uses the database of foods that everyone uses, and your age and gender do matter!