Older research suggested that people eating plant-based diets might have lower calcium needs. Back in the 1990s, research suggested that animal protein pulled calcium out of bones, raising requirements for those who ate lots of meat, milk and eggs. At one time, we thought that this explained the lower rates of hip fractures in countries with lower animal protein intakes.
While some vegan nutrition websites and books still promote this idea, it hasn’t held up to scientific scrutiny very well. More recent evidence suggests that protein is not harmful for bone health and that it may even be beneficial (2-5). And while getting calcium from plant foods may have a number of advantages for bone health (see below), there is no reason to think that vegans need less calcium than anyone else.
Calcium Requirements and the Impact of Bioavailability
Both the Institute of Medicine (the government agency that establishes the RDAs) 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.
But calcium absorption varies widely, depending on a number of factors including the food source. Calcium absorption from cow’s milk, the standard against which other foods are compared, is about 30%. Absorption rates are about the same for calcium-set tofu and for many fortified plant milks. Absorption rates for other plant foods, though, vary from as little as 5% to as much as 65%. Vegans need to make sure they are consuming foods that are not only good sources of calcium, but good sources of well-absorbed calcium.
Here are a few general observations about calcium content and absorption rates of different plant foods.
- Leafy green veggies are often rich in calcium, but some of them are also high in oxalates, compounds that bind calcium and reduce its absorption. High-oxalate vegetables include spinach, beet greens, and chard. Even though these foods contain calcium, you won’t absorb much of it so they should not be considered good sources of calcium (6).
- Kale, mustard greens, turnip greens and broccoli are low in oxalates so we absorb calcium from these foods very well. Absorption rates vary from 50 to 65% for these cruciferous vegetables. Collard greens are a little bit higher in oxalates but are also very rich in calcium and can be considered a good source of this nutrient.
- Beans, nuts and seeds provide moderate amounts of calcium that is absorbed at relatively low rates. Soaking nuts and seeds can improve absorption. Calcium absorption from soybeans seems to be higher than from other beans.
- Calcium-set tofu—usually made with calcium sulfate—varies widely in its calcium content depending on how it is made. Its calcium is well-absorbed, though, at about 30% (7).
- Calcium absorption from fortified plant milks is similar to absorption from cow’s milk when the type of calcium added is calcium carbonate. It’s a little lower when tricalcium phosphate is used, but still good at about 25% (8). (And yes, it’s important to shake the carton since the calcium can settle to the bottom.)
- Calcium absorption from fortified fruit juices seems to be at least as good as from cow’s milk, or probably better (9).
Best Calcium Choices
The absorption issue matters a lot when thinking about meeting calcium needs. For example, 3 cups of cooked turnip greens would give you only 600 mg of calcium compared to the 900 mg you would get from 3 cups of cow’s milk. But you’d end up absorbing about the same amount of calcium—around 300 mg—from either one since the absorption rate for turnip greens is so high.
It would be tedious to track all of these absorption rates, and we don’t have this information for very many foods anyway. But, you should have no trouble meeting calcium needs if you consume at least 2 cups per day of foods that are rich in well-absorbed calcium. These include cooked Chinese cabbage, turnip greens, mustard greens, collards, calcium-set tofu, fortified plant milks and fortified juices.
Those two cups won’t provide you with all the calcium you need, but a few servings of other foods that provide calcium can easily make up the difference. These include beans, almond butter, soaked almonds, broccoli, kale, okra, sweet potatoes, figs, navel oranges, corn tortillas, and blackstrap molasses.
If you are over 50, aim for at least 3 cups per day of the foods that are rich in well-absorbed calcium since older people may absorb calcium less well. If you don’t eat these foods often or are otherwise worried about meeting needs, it’s fine to take a small supplement of 300 mg or so. Absorption from supplements is generally good. Take calcium pills with meals to reduce the risk of kidney stones.
Getting calcium from fruits and vegetables might have some advantages since diets rich in these foods are linked to improved bone health (10). This may be because plant sources of calcium are often high in potassium, vitamin C, and vitamin K, all of which may be important for keeping bones strong. There has also been interest in the idea that isoflavones in soymilk and tofu might protect bone health, but the findings on this are conflicting.
So, bottom line: Vegans cannot ignore calcium, but it’s relatively easy to get enough. And there may be benefits for everyone to getting calcium from plants.
For more information about calcium, see this article on the Vegan Health website.
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