Adélaïde,

Good catches. I was trying to illustrate that the National Academies don’t expect someone to absorb 1,000 mg of calcium per day because many people don’t realize that only a percentage of most nutrients is actually absorbed. I’ve changed it to:

The adult DRI for calcium was set largely from balance studies of people eating typical mixed diets, in which average calcium absorption was about 25% (see p. 38 in Dietary Reference Intakes, 2011). In other words, the DRI implicitly assumes an absorption rate of roughly 25%; foods with higher absorption provide more usable calcium per milligram, and foods with lower absorption provide less.

I also changed the “%” to “fraction” in the table.

I’m french, so sorry for my english.

You said “The DRI for calcium is roughly based on an average absorption of calcium from foods of 25% (p. 38 in Dietary Reference Intakes, 2011)” but the document p38 say : “From a recent series of controlled metabolic studies undertaken by the USDA, mean calcium absorption (also referred to as “fractional calcium absorption,” which is the percentage of a given dose of calcium that is absorbed) in men and non-pregnant women—across a wide age range—has been demonstrated to be approximately 25 percent of calcium intake (Hunt and Johnson, 2007).
National Academies of Sciences, Engineering, and Medicine. 2011. Dietary Reference Intakes for Calcium and Vitamin D. Washington, DC: The National Academies Press. https://doi.org/10.17226/13050.”
This sentence doesn’t show that DRI is based on a average absorption of calcium from foods of 25%.
Is it your owner conclusion ?

There is an error on the document (very interesting) : https://docs.google.com/spreadsheets/d/e/2PACX-1vQYxFoxKMjpMSJBn0ojdax4F_j6r_pg_GJUGAYLcvz6mvQORVK7zOr3bh6YftQgXod-h3ho617Gk9kJ/pubhtml
Calcium absorption is gived in %. But 0,42% of 250 isn’t 150. Can we delete the “%” ?

Good evening.

Mike,
It’s because the research on calcium and health is only based on calcium from food. You can assume calcium from tapwater is “a wash.” In other words, if research shows people need 750 mg of calcium from food, but it’s really 750 mg from food + 60 mg from tap water, then the resulting recommendations would be for a total of 810 mg. But if you know that your tapwater is higher than average, then factoring in the amount above average as part of your daily intake seems reasonable to me.

Kevin,
Unless someone has iron deficiency (in which case they shouldn’t take a calcium supplement with an iron supplement), it probably doesn’t make a lot of difference. It’s best not to take calcium and zinc supplements at the same time.

TZ,

Koeder and Perez-Cueto cite Weaver and Plawecki (1994) who compare the difference between calcium absorption from sesame seeds and nonfat dry milk in rats to humans. Since it’s not a direct measurement of calcium absorption in humans, I don’t consider it reliable.

Hi. I’ve found information about bioavailability of calcium from food. Sesame seeds included (~20% absorption rate).
https://doi.org/10.1080/10408398.2022.2107997

Francis,

I’d never heard of calcium carbonate nanoparticles until now. I did a quick search using AI and found this:

While research on the long-term effects of calcium carbonate nano- and microparticles in supplements is ongoing, studies suggest that they are generally considered safe and well-tolerated, with minimal evidence of significant harm.

Safety and Tolerability:

Calcium carbonate, a common form of calcium supplement, is generally considered safe for most people when taken in recommended dosages.

Some studies even suggest that calcium carbonate microparticles may reduce gastrointestinal side effects compared to conventional calcium supplements.

The viability of cells was not negatively affected by calcium carbonate nanoparticles, and in some cases, even showed a stimulative effect on cell viability.