Is it really reasonable to obtain the recommended calcium intake on an unfortified and strictly vegan diet?

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It all started with an argument.

Opening the refrigerator door. I say to my wife, scowling, “Why do we have so much cheese? We have talked about this.” Compared to milk, cheese is less nutrient dense and contains more calories. I find it very easy to overeat cheese, and this undermines my ability to stay lean while I put on muscle. I also don’t care for the dairy industry. And I want to instill good eating habits in my kids; I want them to treat foods like cheese as what I think they are: indulgence foods for special occasions. Not something for regular consumption in the house.

My wife, who is taking a nutrition class, responded: “Dairy has a lot of calcium.”

I shoot back, “There are better sources of calcium.”

She responds, levelly, “Yes, but they are not nearly as bioavailable or rich in calcium as dairy.”

My jaw dropped as I stared at her blankly. I sat down at my computer to begin wife-fact-checking. She might be right, or she might not be. But by the end of this, I would understand more about calcium.

How much calcium do humans need?

I started with a Google search and came upon this post by the National Academy of Sports Medicine, which provided the following two tables:

Gotcha wife. You’re wrong!

But was she? I looked closer at the numbers, especially in the far-right column.

It quickly became clear that while some vegetables provided a higher % of absorbable calcium of total available than milk, milk by far provided more total absorbable calcium PER SERVING. Just take another look:

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So how many veggies do I need to get my calcium?

Then I started looking at the recommended calcium intakes. That’s when my eyes opened wide. If milk provides only 96.3 mg of calcium in a 240 g serving (about 240 mL), and the recommended intake for adults is around 1000 mg/day, then that would mean that more than 240 mL x 10 = 2.4 liters of milk per day are necessary to meet the recommendations.

And since milk way more calcium than everything else, that’s going to mean a lot of servings of everything else. We’re talking pounds and pounds of vegetables. 6.2 pounds of kale, 7.3 of broccoli, 14.2 of Brussels sprouts. No way!

Fortunately, that’s not quite right. It turns out that the Institute of Medicine takes this into account and provides a rough estimate of TOTAL calcium. This causes the numbers to settle down.

For milk at least.

For the rest?

9 pounds of Brussels sprouts
4.5 pounds of Broccoli
3.1 pounds of kale
0.8 liters of milk

Not looking so great for our cruciferous friends. It turns out that my wife had a point.

Manageable by the average vegan

OK, but if kale calcium for example is twice as absorbable as milk calcium, shouldn’t it get a handicap relative to milk?

For instance, what if because milk calcium was 32.1% absorbable, and broccoli was 61.3% absorbable, we multiply the broccoli calcium by 61.3/32.1, or 1.9? And do that for the remainder of the foods, as well?

In that case, we get:

Brussels sprouts 4.5 pounds
Broccoli 2.4 pounds
Kale 2.1 pounds

That’s still a LOT of food. It should be noted that a VERY LARGE salad is about 200 grams of leaves. 2.1 pounds is about 1 kilogram. So we are talking 5 very large salads each day to meet the calcium recommendation by the Institute of Medicine.

What about the other foods listed? Here’s what a final calculated table would look like:

8 pounds spinach
6 pounds cooked pinto beans
4.5 pounds Brussels sprouts
2.4 pounds broccoli
2.1 pounds kale
1.1 pounds almonds (2880 calories)
~1 pound collards*
0.8 liters milk

* It turns out that collard greens contain some of the highest amounts of calcium per serving in any food.

What would a typical diet with adequate calcium look like? Something like this:

100g almonds, 1-2 pounds of beans, and 3 large kale salads per day.

Or 4 pounds of beans, 1 kale salad, and some almonds.

Theoretically possible for sure, but manageable by the average person? Probably not.

Are the Institute of Medicine recommendations high? Recommendations from around the world

It might be suggested that the Institute of Medicine’s recommendations might be a little high. Yet the IOM’s recommendations are similar to other organizations around the world. Britain’s National Health Service recommends 700 mg per day. Nordic recommendations are between 800 mg and 900 mg per day. The European Food Safety Authority recommended 950 per day.

In fact, in 2003, the World Health Organization put the minimum (rather than recommended) calcium intake to prevent osteoporosis at 400-500 mg. That means that just half of the calcium intake as proposed above will pull a person into the range for potential osteoporosis.

Is fortification the answer?

There should be no doubt that it is theoretically possible to achieve adequate recommended calcium intake on a strictly vegan diet without fortified foods. However, the question is whether such a diet is likely to be reasonable for most people at the present moment. The answer to that question is emphatically no.

There is some question, moreover, about whether fortification itself is optimal. Recent evidence suggests a connection between calcium supplementation and cardiovascular disease–but no connection between dietary calcium and CVD–and the dominant explanation is that supplementary calcium might be too rapidly absorbed. Therefore, if fortification is pursued, it may be best to avoid foods that might be expected to be digested and absorbed particularly rapidly (e.g. soy or almond milk). That said, we just don’t know with certainty. These are just some of my best guesses.

Other alternatives

What we do know is that without eating dairy products–or if you’re Paleo-inclined, bones–it’s not particularly easy to meet the recommendations without eating a high-quality diet rich in leafy green vegetables, or without fortification.

One option for vegans is calcium-fortified tofu. A single block per day (~500g) will provide for nearly the entire recommended daily calcium. If you’re thinking about going or staying 100% plant-based, that might be an important option to consider.

Another option is abandoning a strictly plant-based diet and consuming fish, especially sardines. A serving of just 3 ounces of sardines provides up to 1/3 of the recommended intake, and may provide health benefits beyond the calcium content, too.

Wrapping up

Regardless of the decision made, for bone and other aspects of long-term health, it is important to consider diet quality and what exactly one is willing to commit to when making the decision to consume a vegan or otherwise plant-based diet. Don’t take it lightly! If you decide to take that step, understand that consuming a plant-based diet while avoiding nutrient deficiency takes a lot more planning and care than when consuming an omnivorous diet. Take the time to do things right. Down the road, you will be happy that did.

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6 Comments

  1. I have been curious about this too. here is a Harvard post on the subject. https://www.health.harvard.edu/staying-healthy/how-much-calcium-do-you-really-need
    as well as Dr. Gregor wondering about higher calcium is related to higher bone fractures
    https://nutritionfacts.org/2017/01/31/why-is-milk-consumption-associated-with-more-bone-fractures/

    if we conclude that 500 to 700 mg is the appropriate figure, then the calculations you did on daily consumption becomes much more reasonable for vegans.

    1. ironically, the countries that have the highest rates of dairy consumption also have the highest rates of osteoporosis and hip fracture in later life

  2. This is what vegan Registered Dietitian (RD) (who also has an MPH) Virginia Messina writes about vegan diet and calcium (she’s also coauthor, with another vegan Registered Dietitian, Jack Norris, of the book Vegan for life: Everything you need to know to be healthy and fit on a plant-based diet. 2011):

    “with just a little bit of knowledge and some attention to food choices, it’s not at all difficult to get enough”
    “bottom line: Vegans cannot ignore calcium, but it’s relatively easy to get enough.”
    https://www.theveganrd.com/vegan-nutrition-101/vegan-nutrition-primers/calcium-a-vegan-nutrition-primer/

    Kevin, there might be a misunderstanding on your part here:
    Messina writes:
    “Both the Institute of Medicine (the government agency that establishes the recommended daily allowances) and the World Health Organization recommend 1,000 mg of calcium per day for adults (or 1200 for those over 50).
    What really matters is how much calcium you absorb, though, not how much you eat. People generally absorb about 25 to 30 percent of the calcium in their diets. For those meeting the RDA, this translates to around 250 to 300 mg of absorbed calcium, which seems to be enough to meet biological needs for this mineral.”

    So, you don’t have to eat 1,000 mg of BIOAVAILABLE calcium per day. The recommended daily allowance already takes into account that you don’t absorb most of the calcium you eat.

    See also (website of Jack Norris, RD): https://veganhealth.org/calcium/

  3. Missing one crucial, extremely simple to consume, food group. Mineral water. 25% bioavailavility of calcium, similar to milk. I buy 1.5 L bottle which contains 700 mg of calcium. Drinking it alone gives me nearly the bioavailable minimum. Add hummus from unhulled sesame and a smoothie or bowl with a cup or two of kale or other dark leafy greens and I probably get more than average milk drinker.

    https://www.researchgate.net/publication/8350087_Calcium_Bioavailability_From_a_Calcium-Rich_Mineral_Water_With_Some_Observations_on_Method

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