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The US RDA for calcium for children 9-18 is 1300mg/day, for which milk and dairy seem like the only reasonable source. The vegetable sources of calcium would need to be eaten in impractically large quantities (e.g. 10 pounds of broccoli), and I’m a little uncertain about the bio-availability of calcium in supplements.

Are bone fractures the only important thing to measure about calcium consumption, or could there be other important factors? Will children not be as tall and strong without that much calcium? Is the US RDA simply wrong?

Certainly, our Paleolithic ancestors weren’t drinking milk or taking supplements, yet they seem to have been just as tall and strong as we are, and maybe more so. Could they possibly have been consuming that much calcium?

Because we want them to be tall and strong, we try to have our kids drink 3 cups of milk per day, but I don't like the extra sugar calories in all that milk, and my kids don’t like it enough to drink that much without battles.

So should we stop worrying about calcium, or do they really need 1300mg/day?

  • Related, possibly duplicate: health.stackexchange.com/questions/657/… and health.stackexchange.com/questions/154/… – JohnP Jun 14 '15 at 14:26
  • They're related, but assume that we need that much calcium and are asking how to get it. I'm asking if we really need that much in the first place. – Joshua Frank Jun 15 '15 at 15:36
  • Aside: extra sugar calories, as in added sugar? There is milk without added sugar. And if the children don't like milk, how about yoghurt or cheese? Or egg yolks, legumes, nuts... It's not about taking a lot of one sort of food that contains a certain nutrient, but about balanced nutrition. Calcium isn't important just for height, but for bone density (and other things, but let's stick to bones for now). Once the susceptibility to fractures is there the problem has already started and is more difficult to reverse than prevent. – Lucky Jun 15 '15 at 19:10
  • I mean the calories from the lactose in the milk. But the bigger problem is that my kids just don't like dairy products enough to get enough calcium that way. But I've read that some people are questioning whether dietary calcium is actually needed in that quantity for optimal bone health, and since Paleo people didn't consume dairy, maybe that is correct. – Joshua Frank Jun 15 '15 at 21:03
  • I think our ancestors got calcium from fruit and animal bones. Though maybe centuries of increasing dependence on cattle milk made our bone structure favor calcium more. – jiggunjer Jun 16 '15 at 9:50
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Humans are strange among mammals in making dairy products such a large proportion of their adult diet. It reminds me of this amusing quote by Henry David Thoreau:

One farmer says to me, 'You cannot live on vegetable food solely, for it furnishes nothing to make bones with;' and so he religiously devotes a part of his day to supplying his system with the raw material of bones; walking all the while he talks behind his oxen, which, with vegetable-made bones, jerk him and his lumbering plow along in spite of every obstacle.

Also, this study seems to be saying that vegetables can supply as much calcium as milk:

Recent absorption studies in humans with low-oxalate and low-phytate vegetables and pulses also showed that contrary to common presuppositions, these vegetables with low calcium chelators do have a comparable calcium absorbability to milk.

But the intake of calcium is just part of the equation - calcium is also lost by excretion, which is what makes oisteoporosis possible. Many studies, such as this one entitled "Excess dietary protein can adversely affect bone", report that high consumption of protein in the diet leads to increased excretion of calcium due to the acids formed in the metabolism of protein.

Finally, an article published on Harvard's own website considers the 1,000-1,200 mg RDA for calcium recommended by the National Academy of Sciences, which were based on short-term studies, and raises them to question based on long-term studies:

In particular, these [long term] studies suggest that high calcium intake doesn’t actually appear to lower a person’s risk for osteoporosis. For example, in the large Harvard studies of male health professionals and female nurses, individuals who drank one glass of milk (or less) per week were at no greater risk of breaking a hip or forearm than were those who drank two or more glasses per week.

The article describes several more studies that found no benefit to bone strength from high milk consumption.

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    Hi Chris. It is possible to get enough calcium from just vegetables, but it would be a monotonous diet. The article states: "In Asian countries, the major sources of calcium are derived from vegetable[s]... fish and shell fish with edible bones, fins and shells, etc." That is relevant. Also, "Humans are strange... in making dairy products such a large proportion of their adult diet." That's because we can. Cats and dogs can't milk cows or make cheese, but trust me, many would drink milk and eat cheese every day of their lives if they could. So please, no conspiracy theories. Thanks. – anongoodnurse Jul 16 '15 at 1:29
  • My reference to other mammals was intended to raise the question why humans should be uniquely unable to stay healthy without dairy product consumption. – Chris Jenks Jul 16 '15 at 18:39
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    After the mutated gene for lactose tolerance appeared in humans in Turkey, it spread faster than wildfire, it was so helpful to European mankind. We can stay healthy without milk; it's just harder, that's all. Not a great medical mystery, just a propitious genetic mutation. – anongoodnurse Jul 16 '15 at 20:15
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According to this review article, adults need a bit more than 1 gram of calcium per day. However, it may be the case that the natural vitamin D levels for the human body should be a lot higher than what is currently the norm, see e.g. here. Calcium is absorbed from the gut by both passive and active mechanisms, the active mechanism is vitamin D dependent. If the level of calcium in the blood drops then calcium from bones will be released and simultaneously, the kidneys will produce more calcitriol which then turns on genes in the gut to produce enzymes that help to extract calcium from food.

Besides the total intake per day, what is also relevant is the presence of big gaps in the intake of calcium. Such gaps will prompt the body to extract calcium from the bones and then you're dependent on processes that will eventually put calcium back into the bones. By spreading the intake of calcium over the day, you can prevent bone loss in the event that in your case this mechanism of putting the calcium back doesn't work as well as it should.

Note that there are many sources of calcium that we tend to ignore. Water can contain calcium, e.g. where I live there is 60 mg per liter. That doesn't sound like a lot, but if you drink 3 liters a day, you'll get 180 mg. Bread only contains 10 mg per slice, but if you eat a lot like I do (I don't recommend doing that unless it fits into a well balanced diet for your case) like 15 slices per day, then that's 150 mg of calcium. So, the dry bread plus water alone is already 280 mg.

Then if you eat 500 grams of broccoli at dinner like I did today, you'll get 235 mg of calcium. Potatoes contain 12 mg per 100 gram, I had 1 kg of potatoes for dinner, so I got 120 mg from the potatoes. This means that in total I got more than 600 mg of calcium from sources one normally doesn't bother to consider. However, it must be said that absorption of calcium from such sources isn't as efficient as from dairy products due to oxalates in vegetables, phytic acids in grains and the lack of phosphorous when you drink just plain water.

So, you see that non dairy sources can give you a decent amount of calcium, but you then need to eat a lot (I eat about 4000 kcal per day, which is a lot more than average). The calorie intake of indigenous people who needed to jog for hours every day to chase prey was likely a lot higher than what it is today for the typical office worker, so they may actually have gotten their gram of calcium per day from only non dairy foods and their vitamin D levels were also likely a lot higher than that of the average office worker.

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    There are some great points in your answer (such as the remark about absorption and oxalates)! However, I have two concerns: 1. "we don't need more than 1g of calcium per day". Who's we? The OP is asking about the value for children, and the study you linked seems to refer to adults. 2. Recommending someone to eat 15 slices of bread a day would require to know a lot about their build, diet, energy expenditure etc (it's not exactly a universally healthy advice). Perhaps you could rephrase that part so it doesn't sound like a direct recommendation? Otherwise, it's a good answer :-). – Lucky Jul 19 '15 at 16:34

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