Is the RDA of Calcium based on what needs to be absorbed or the calcium food content to be consumed?

[Feenicks]

Is the recommended daily amount of Calcium based on what needs to be absorbed by the body, or amount of calcium content in the food to be consumed?

That might sound like the same thing.. however I've read that calcium is never 100% absorbed or at least not from food. For instance absorption from cheese and milk is 32%, and broccoli is almost double at 61% according to this link: dairynutrition.ca/nutrients...

Previously I considered a standard 125 grams supermarket ball of Mozzarella giving me 913 mg of calcium so I'd cut it in half as body can only absorb upto 500 mg in one two hour window, e.g. I'd absorb 456 mg of calcium from half a ball and that would be almost half of my daily requirement. Apparently though I am only going to be absorbing 32% of that 456 mg which means just 146 mg of calcium from eating half a ball of mozzarella (i.e. 14.6% of my daily requirement and not 45.6% where 1,000 mg is my recommended daily dose). So as an example would I need to effectively multiple by 3 the amount of mozzarella I consume to meet near on half of my daily requirement?

I am assuming from the disparity between broccoli and cheese calcium absorption that the 1,000 mg RDA is for absorption not calcium content in the food. So for me to get 305 mg of calcium absorbed I'd need to eat 500 mg of Broccoli calcium or 1,000 mg of cheese calcium.

In addition, I am taking Calcium citrate 300 mg day, usually once per day. What is the absorption rate on an empty stomach (nothing consumed 2 hours either side)?

[Met00]

My understanding is that the RDA is the intake they recommend, as it would be very difficult to calculate what's being absorbed. You wouldn't absorb from supplements any better than from food. Calcium calculators work out how much is in the food, not how much you're likely to absorb. The one I use bases it on 700mg calcium content of the different foods.