Articles · Nutrients
Calcium beyond the milk carton
How much calcium your bones need, which foods carry it (some surprising ones), why spinach isn't the answer you'd expect, and what vitamin D has to do with it.
· 4 min read
"Drink your milk, it's good for your bones." Most of us grew up hearing it. It's true that milk is an easy source of calcium, but it's far from the only one. What if you don't drink milk, can't, or simply prefer not to? And why does a mountain of spinach not count as much as it seems?
Why calcium?
Almost all the calcium in your body, about 99%, is in your bones and teeth. The rest does busy work: helping muscles contract, nerves send signals and blood clot. If you don't get enough from food, the body borrows from the bones to keep the blood level steady. Over years, that borrowing can leave bones thinner and more likely to break.
In the United States, adults are advised to get 1,000 mg a day, rising to 1,200 mg for women over 50 and everyone over 70. In the UK, the recommendation for adults is 700 mg.
Think about it: Without looking anything up: how many of yesterday's meals had a good source of calcium in them?
Where can you find it?
Roughly how much calcium these portions bring:
- A glass of milk (250 ml): about 300 mg. Yogurt and cheese are rich too.
- A glass of calcium-fortified plant drink (soy, oat, almond): often 300 mg, but check the label, because not all are fortified.
- Tofu made with calcium sulphate (the label says so): often 200–400 mg per 100 g.
- Canned sardines or salmon, eaten with their soft bones: around 200–350 mg per small tin.
- Kale, pak choi or broccoli: smaller amounts per portion, but well absorbed.
- Almonds, sesame seeds and tahini, white beans and dried figs add a little more.
The spinach surprise
Spinach is rich in calcium on paper, but it's also rich in oxalate, which binds much of that calcium so the body can't take it up. In one study, people absorbed only about 5% of the calcium in spinach, against 28% from milk. Kale and pak choi, on the other hand, are low in oxalate: in another study, the calcium in kale was absorbed a little better than milk's (41% against 32%).
So enjoy spinach for its other virtues, like folate and vitamin K, but don't count on it for your bones.
The Milkmaid, Johannes Vermeer, c. 1660, Rijksmuseum, Amsterdam. A kitchen maid pours milk in a thin, steady stream, with stale bread on the table; she may be making bread pudding. Vermeer made a whole painting out of a quiet moment and a jug of milk. Public domain · Wikimedia CommonsCalcium needs a partner
Your gut can only absorb calcium properly with enough vitamin D. That's one reason bone health tends to suffer in winter and in people who spend little time outdoors. Our article Vitamin D in winter explains how to keep it up.
Moving matters too: bones get stronger when they carry weight. Walking, dancing, stair climbing and muscle-strengthening exercise all help.
Try this: If you don't eat dairy, choose a plant drink with "calcium" in the ingredients, give it a shake (the calcium settles at the bottom), and add tofu made with calcium sulphate to a stir-fry this week.
Can you have too much?
From food, it's very unlikely. From supplements, yes: more isn't better, and high doses can cause constipation and, in some people, kidney stones. The upper limit for adults is 2,000–2,500 mg a day from all sources. If you think you need a supplement, ask your doctor or pharmacist first.
Think about it: Do you take a calcium supplement on top of a diet that already has plenty? It's worth adding it all up once.
Quick quiz
Why does spinach count for little calcium, even though it contains plenty?
It's rich in oxalate, which binds much of its calcium: in one study only about 5% of it was absorbed.
Which green vegetable's calcium is absorbed about as well as milk's?
Kale (pak choi and broccoli too). They're low in oxalate.
Which vitamin does the body need to absorb calcium?
Vitamin D.
Sources
General information, not medical advice. If you have a health condition, are pregnant or take medication, ask a doctor or dietitian what is right for you.