March 7, 2009

The Lowdown on Calcium

Calcium is one of the most misunderstood nutrients.

The range of confusion varies from those who think dairy products contain the most absorbable type of this mineral to people who think spinach is a great source of calcium.

Let's clarify these points.

Are dairy products a good source of calcium? Yes. After all, eight ounces of milk provide a third of the daily value of calcium.

Are dairy products the only way to get calcium? Absolutely not.

Do dairy products provide calcium with the highest bioavailability? No.

Consider the following:

Eight ounces (one cup) of milk contain 300 milligrams of calcium.

A half cup of cooked bok choy provides 79 milligrams of calcium.

To someone unfamiliar with nutrition, the conclusion might seem obvious: "I need two cups of bok choy to get as much calcium as a cup of milk!"

Alas, nutrition science isn't always as obvious as it seems.

You actually only need one and a quarter cups of cooked bok choy to match the calcium you would get from a cup of milk since the calcium in bok choy is more absorbable than the one in dairy products.

The same thing happens with Chinese cabbage. A half cup of this cooked vegetable offers 239 milligrams of calcium, but that equals the amount of absorbable calcium in a cup of milk.

Let's now turn our attention to spinach. I am continually amazed by the amount of self-touted (though, clearly, not really) nutritione experts who list this vegetable as a good source of calcium.

A half cup of cooked spinach offers 115 milligrams of calcium. However, due to its high amount of oxalates (organic acids naturally found in spinach that inhibit calcium absorption), it takes EIGHT cups of cooked spinach to equal the amount of absorbable calcium in one cup of milk.

It just so happens that unlike spinach, the Brassica family of plants -- including broccoli, kale, bok choy, cabbage, and mustard greens) does not accumulate oxalate, thereby providing highly absorbable calcium.

I know some people like their nutrition advice in absolute form ("NEVER eat this, ALWAYS eat this), it's not my style.

My suggestions provide you with plenty of choices. If you like milk, drink it -- it provides a significant amount of calcium.

If you don't like it or don't want to include it in your diet, no need to worry about calcium as long as you include greens from the Brassica family and other non-dairy sources (tofu, tempeh, almonds, calcium-fortified alternative milks, etc.) in your diet.


T said...

Does red cabbage contain calcium? We eat alot of it in my kids love it!

Also...I see that broccoli has a good about of absorbable calcium...does it matter raw or cooked?


Edie said...

Yep, we all need degrees in nutrition these days to make sense of all the expert opinions. I appreciate how you explained the differences between sources as to their bio-availability for our bodies.

Vincci said...

Hey Andy,

Thanks for this article - I was wondering if you had any sources for more information about the bioavailability of calcium in different foods because I'm having trouble finding something that's consumer-friendly!

I'm of the camp that's a little skeptical that dairy foods are as important as they are made out to me and it frustrates me that even in Hong Kong, where dairy is not a part of the traditional diet, the food pyramid that dietitians use there is just based off of the old USDA pyramid!

I know I'm kind of going off on a tangent now, but I really think more resources should go into looking at healthy patterns of eating in other parts of the world, instead of trying to convert everyone to a "western" diet.

Andy Bellatti said...

Hi Vincci,

My stance on dairy products is neutral. They certainly offer nutrition, but a perfectly healthy diet can be 100% dairy-free.

As you mention, some populations (and particular native Asians) have a hard time digesting dairy and, in my opinion, should NOT be getting the message that "it's dairy or nothing."

I think you will find this study interesting:

And then there's this:

I haven't seen any consumer-friendly charts with this information. Worrying, don't you think?