Calcium for the milk-averse
Ever find it curious that the majority of African/African-American, Asian, Hispanic and Jewish adults are at least somewhat lactose-intolerant, and yet the USDA Food Pyramid recommends that we all consume 3 servings of dairy per day? Ever wonder why everyone in Asia isn’t keeling over with broken bones despite the fact that cow’s milk is not a part of the traditional Asian diet? Ever hear your vegan friends protest that humans are the only species who drink the milk of another species? In other words, ever wonder why our body needs so much darn calcium if dairy products are so problematic for so many of us?
Well apparently it wasn’t always this way. According to the veritable clinical nutrition bible, Modern Nutrition in Health and Disease, once upon a time, we humans used to get plenty of calcium from our nomadic diets rich in “roots, tubers, nuts and beans.” (Generally, plant roots contain the highest levels of calcium, and grains/fruits accumulate the least calcium.) As the nomadic lifestyle gave way to settlement patterns based around domesticated grains and animals, the human diet shifted toward dietary patterns and food processing methods that resulted in significantly less dietary calcium. The result? Dairy foods–made possible by the domestication of various animals– became the most important source of calcium in our Western diet. (But still, in a certain parts of the world, people get their calcium primarily from some combination of green vegetables, soybean products, beans, corn milled on limestone and/or root vegetables.)
But no matter how we ended up here, the fact remains that most adults need 1,000mg of calcium/day, and most adults do not get 1,000mg of calcium/day. Teenagers need even more: 1,300mg/day, and adults over the age of 50 need 1,200mg/day*. That’s a lot of calcium, even for people who like dairy,who eat dairy regularly, who digest dairy perfectly well and who have no philosophical objections to eating dairy products. If it were easy to get it all in, then the majority of Americans wouldn’t be falling short of the goal.
The reference amount for a serving of calcium tends to be 1 cup of milk, which has about 300mg of relatively bioavailable calcium. You may have heard that the average adult is supposed to consume the equivalent of about 3 cups of milk per day to reach the recommended 1,000mg. In dairy currency, the equivalent of 1 cup of milk would be 6-8oz of yogurt (depending on the type); or 1.5 oz of most hard cheeses (one standard 1oz piece of string cheese has about 200mg of calcium, so it’s still a very good–and very convenient–source). Some softer cheeses–like brie or cottage cheese, for example–have significantly less calcium.
But what about non-dairy sources? What’s would be equivalent sources of comparably bioavailable calcium? (This is good information here, people. Good luck trying to squeeze it out of the USDA’s Food Pyramid…)
Studies have shown that soymilk fortified with calcium carbonate provides as much bioavailable calcium as does an equivalent amount of cow’s milk. Ditto for most calcium-fortified orange juices. So 1 cup of either such product would be a good substitute for 1 serving of dairy. If your soymilk is fortified with calcium triphosphate, you’ll need about 1.3 cups to absorb the same amount of calcium that’s in a cup on cow’s milk.
You may have heard that several vegetables are good sources of calcium, too. While this is true, multiple factors can impact the bioavailability of calcium from plant sources. These include the presence of natural compounds called oxalates and phytates– both of which can bind to calcium in the digestive tract and prevent it from being absorbed. So when you consider vegetable sources of calcium, it’s not enough to know how much calcium they contain as it’s written on the label, but how much calcium you’ll actually be able to absorb.
Members of the Brassica genus of vegetables–which are any plants related to cabbage–are the most commonly cited as good sources of calcium. For good reason: the calcium in these vegetables is very bioavailable owing to the low levels of oxalates they contain, but you’ll still have to eat a lot of many of them in order to absorb the equivalent amount of calcium that you’d absorb from 1 cup of cow’s milk. For example: ~3 cups of chopped broccoli; ~3 cups of chopped kale; 2-2.5 cups of bok choy. The best I’ve come across are chinese mustard greens, where ~1 cup chopped has the same amount of bioavailable calcium as milk. Don’t let some of these large portions discourage you from relying on these vegetables as a key source of calcium in your diet! A more standard portion of 1 cup of most raw Brassica vegetables (which for leafy vegetables will cook down to about 1/2 cup) will typically have at least a very solid 10% of your daily calcium needs (on average; exact amounts will depend on the specific vegetable), so eating average portions of these types of vegetables daily will add up and make a significant contribution toward meeting your calcium goal. Not to mention a significant contribution to your goal of eating a diet rich in vegetables! Other vegetables in the Brassica family include: cabbage, cauliflower, brussels sprouts, mustard greens, collard greens, turnip greens and kohlrabi.
You may also have heard that spinach is a good source of calcium. And it is! But alas, spinach is plagued by relatively high levels of both oxalates and phytates, and its calcium is very poorly absorbed (only about 5% of its calcium content is absorbed, compared to about 60% for kale and broccoli). It’s not a good source of bioavailable calcium, but it’s very healthy for all sorts of other reasons, so don’t break up with it. Just don’t count on it to help you inch your way to the holy grail of 1,000mg.
While beans are a decent source of calcium, they tend to have too many phytates and oxalates to allow you to absorb very much calcium. Of the beans, white beans are reportedly one of your best bets for calcium: approximately 2 cups of cooked white beans should provide the same amount of bioavailable calcium as a cup of milk, which means a more-likely portion of 1 cup still offers a very respectable 15% of your daily needs. Speaking of beans, tofu that is set in calcium will be a good source of bioavailable calcium, too. (Look for calcium sulfate on the ingredient list.) You’ll need about a 5oz serving (a bit over 1/2 cup… a bit less than 3/4 cup) to absorb the same amount of calcium as you would from 1 cup milk. So even a slightly smaller standard portion of tofu will contribute significantly to your reaching your calcium intake goals.
OTHER LESSER-KNOWN CALCIUM-RICH FOODS
There are several other foods that are pretty good sources of calcium (~10% of the daily value per serving) for which I could not find bioavailability data. I will mention a few here only because they tend to be less well-known. They include dried figs, sesame seeds/sesame tahini, canned salmon with the bones, sardines, blackstrap molasses, toasted unblanched almonds, and boiled soybeans (edamame). If you like any of these foods, it’s a good idea to include reasonably-sized portions of them in your regular diet. As you will see from the information above, every little bit helps! Your best bet to meet your daily calcium goals is to eat a varied diet that includes cruciferous vegetables (especially the dark leafy ones), beans, tofu, fish, dairy (if you like it), fortified foods/drinks, nuts and seeds.
PREVENTING CALCIUM LOSSES
Now once you’ve gone through all of the trouble of taking in sufficient calcium, don’t go throwing it away! Sodium and calcium share the same transport systems in your kidneys, so when you excrete sodium, it takes calcium along with it. In other words, eating a high-sodium diet means your body has to get rid of a lot of sodium to keep its fluid balance intact, and this will have a significant impact on how much calcium you’re able to retain. The vast majority (almost 80%) of sodium in a typical American diet comes from processed foods and restaurant meals…so the more you cook at home with fresh, minimally processed foods, the better you’ll be able to control your sodium intake. Certain foods are notoriously high in sodium, so start paying attention to those nutrition facts labels: frozen entrees, frozen veggie burgers/meat substitutes, processed/cured meats, canned anything and especially canned soups, broths, condiments of all kinds, soy sauce, miso, pickles/olives, and chips/pretzels/salty snacks. The recommended maximum sodium intake is 2,400mg/day, so try to pay attention to your intake so you can protect your calcium.
So what if after all of this effort, you still fall short of your calcium goals? This, in my opinion, is why god created the calcium supplement. (I take 500mg a day to bridge the gap between what I estimate my regular diet provides and what I know I need to take in. There’s no shame in that.) If you choose to take a supplement, there’s no point in taking one with more than 500mg per dose, as the body cannot absorb more than that at once. So if you do choose to take a full 1,000mg/day, it would be best to split that up into two separate doses of 500mg each, once in the morning and once in the evening. Most calcium supplements also contain Vitamin D, which is a good thing; this helps your intestines absorb the calcium. You’ll see several forms of calcium used in supplements. Calcium carbonate is best absorbed with food. Calcium citrate can be taken on an empty stomach. The only calcium supplement that benefits you is the calcium supplement you actually take. Don’t buy a huge horse pill if you hate swallowing it, because then you won’t take it. Also, pay attention to the number of pills in a “serving.” If the label says that 1 serving provides 500mg of calcium but the serving size is 2 pills, then you need to take both pills in order to get the 500mg. (I know this sounds obvious, but when is the last time you read a serving size on a vitamin pill label?) I know that those Viactiv calcium chews are very popular, and I think that they’re fine if the caramel/chocolate flavor helps motivate you to take them regularly. Just be aware that they are not calorie-free and they’re made mostly of sugar. (Not to sound like a grinch; it’s only 20 calories per chew, so I think most people can find room in their daily calorie budget for that.) They also contain calcium carbonate, so you should take them with a meal to ensure you can absorb the calcium efficiently. The last point I’ll mention about supplements in general is that they’re not at all regulated by the FDA, so you have no way to know for sure that they contain what the label says they contain. Scary? You betcha. If this concerns you, you can visit consumerlab.com and subscribe to their service. They’re an independent lab that tests dozens of brands of vitamin, mineral and herbal supplements and reports on whether they contain what they claim to contain. If you take a lot of supplements, this may be a subscription worth investing in.
Hopefully, this information will be of use to you in cobbling together a calcium strategy to help you meet your needs. If you have any other strategies that work for you, feel free to share!
*Why do we need so much calcium? In children and adolescents, it’s to build bone mass. In the rest of us, it’s to prevent our mature bones–which you can think of as a calcium bank– from being robbed by bone cells who would break down the bones in order to supply calcium to maintain steady blood levels. When your bone cells make more withdrawals than deposits over the course of your adult life, you get osteoporosis.
ME Shils, JA Olsen, M Shike, AC Ross (eds). Modern Nutrition in Health and Disease, 10th edition. Baltimore: Lippincott Williams & Wilkins; 2006.
Heaney RP, Weaver CM. Calcium Absorption from Kale. Am J Clin Nutr. 199o;51(4):656-7.
Weaver CM, Proulx WR, Heaney R. Choices for achieving adequate dietary calcium with a vegetarian diet. Am J Clin Nutr. 1999;70(3 Suppl):543S-548S.
Weaver, CM. Calcium in Present Knowledge in Nutrition. Washington, DC: ILSI Press; 2001
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