Calcium is a very important mineral in human metabolism, making up about 1-2% of an adult human's body weight. In addition to its widely known role in bone structure, calcium is used to help control muscle and nerve function, as well as to manage acid/base balance in our blood stream. From this very simple description, you can see how calcium-rich foods can play a role in many aspects of your health that extend far beyond the specific area of bone health.
While the most common problem related to calcium metabolism is undoubtedly bone loss from getting too little calcium, there can be problems when intake of this nutrient gets too high as well. Excess calcium can deposit in places where it doesn't belong, including blood vessels and the kidneys (in the form of kidney stones). There is still some debate about how much of a problem this is for the average adult, but at this time, most nutrition experts agree that excess dietary calcium is very unlikely, and probably the result of a diet that is largely dependent upon dairy foods.
Dairy vs. Non-Dairy Food Sources of Calcium
Contrary to popular belief, you do not need to eat dairy foods to get the calcium you need in your meal plan. Calcium is provided by a wide variety of foods, and in order to get 1,000 milligrams per day (the Dietary Reference Intake, or DRI for women and men 19-50 years of age), you don't need cow's milk, yogurt, cheese or butter. Consider some of the following examples:
As you can see from the examples above, many non-dairy foods can provide you with substantial amounts of calcium. Particularly helpful in this regard are green leafy vegetables like spinach, collard greens, mustard greens, turnip greens, and kale. Many fish and shellfish—including scallops and sardines—also provide concentrated amounts of calcium. Finally, a very helpful non-dairy food for boosting your calcium intake is tofu. One of the reasons for tofu's rich calcium content involves the tofu production process itself since calcium is often used to help cause precipitation of the soy milk (i.e., conversion of the soy milk into a more solid form). If you do enjoy dairy foods and want to enjoy them regularly in your meal plan, they can be a very effective way of providing you with large amounts of absorbable calcium. However, if you want to avoid dairy foods altogether, it is definitely possible for you to do so while obtaining all of the calcium you need from other foods.
At any given time, about 99% of our total body calcium stores are found in bones and teeth. This calcium plays a critical role in maintaining structural integrity of our skeleton. While calcium is the most critical nutrient to skeletal health, other nutrients provide important support to help absorb and use calcium in the bones. These nutrients include vitamin D, vitamin K, and magnesium.
It may sound counter-intuitive, but bone is very metabolically active tissue, with bone being built and broken down constantly. When our dietary calcium levels are too low, we pull calcium from the bones to keep the blood levels close to constant. As long as we correct this imbalance more days than not, this borrowing and returning process works very well. But if we do more borrowing from than replenishing to our calcium stores, bone can become dangerously weak.
In some sense, this gives us flexibility with our diets. In other words, we do not have to get a full supply of calcium each day, as long as we reach our goals most days. As long as your diet contains a wide variety of the foods on our World's Healthiest Foods list, we believe that your calcium intake should be sufficient to maintain strong bones.
Note that we tend to think of low bone mineral density, or osteoporosis, as a disease of the elderly. While it is true that the bone fractures that occur tend to be in older adults, the damage that leads to osteoporosis can start very early with poor dietary choices during childhood and adolescence. In fact, the pre-teen and teen years are arguably the most critical time to meet dietary calcium needs, as nearly 40% of total adult bone mass is established between the ages of 10 and 15 years.
While it is clear that there is a level of dietary calcium below which bone integrity is compromised, it is not at all clear that lack of dairy products (or dietary calcium in general) is associated with increased risk of osteoporosis in all populations. In fact, most of the evidence for the protective effect of dairy has been in children and adolescents. In adults, however, recent research reviews have been unable to show a significant protective effect of dietary or total (e.g., diet plus supplements) calcium intake against bone loss.
Calcium is an absolutely critical nutrient in regulating acid/alkaline balance (called pH) in the blood. When blood pH starts getting low (down to 7.35 from a baseline of 7.4), calcium starts getting released from the bones to bring acid/base balance back into balance. A complex set of hormonal interactions manages this process, and it is tightly regulated. The pH of blood is of critical importance to sustain life, and controls processes as varied as breathing rate and the ability to transport oxygen in blood cells.
While this process requires no conscious attention, it is very important toward understanding the risk of bone loss with aging. Diet and lifestyle choices that drive more of this leeching of calcium from the bones will increase need for dietary calcium over time.
Because the rate of calcium loss from the bones varies so much from individual to individual, determining the average calcium daily need for the population is a difficult process. Perhaps the easiest way to understand this problem is to think about calcium stores as a bank account, so that when calcium in is equal or greater than calcium out, your balance stays in the black. But when calcium loss exceeds the intake, even by small amounts, you'll end up in deficit. Note that by this math, children and adolescents are going to need to do more than just achieve balance, as they may add as much as 400 mg of calcium to growing bones each day.
Note that acid/alkaline balance of the diet has become a hot topic in the nutrition and physical training cultures. We believe that outside of the effect of balance of the key minerals (calcium, magnesium, sodium, and potassium), focusing on acid/alkaline balance of foods is neither necessary nor beneficial. Most healthy diets tend to be on the alkaline side—although people's definitions of acid/alkaline foods vary from source to source—but that this is more because these healthy diets tend to be rich in plant foods that act as good sources of important minerals.
As we'll discuss below, foods that are heavily salted tend to lead to loss of calcium in the urine. Because of this, it may be helpful to focus more on sources of calcium that contain less sodium (e.g., lightly cooked greens versus types of cheeses that require large amounts of salt in their production).
When a muscle cell receives a signal from nerves telling it to fire that cell responds by allowing a flood of calcium into the cell. This abrupt change leads to a cascade of activity and has the effect of making the muscle cell contract. If calcium levels are abnormal, either too high or too low, this process can be interrupted, which will lead to muscle spasm.
Regulation of the balance of calcium inside and outside of nerve cells is involved in helping to control the flow of sodium in and out. This sodium flow is how the nerves conduct signals to and from the brain. Like the muscles, abnormal calcium concentrations in the blood stream may adversely affect the ability of the nerves to transmit signals.
Because our bodies have such extensive calcium stores to draw upon to keep blood levels constant, it is very unlikely that simple dietary deficiencies would contribute to problems in these activities for most people. The combination of organ disease (particularly kidney disease) and/or hormonal problems (particularly vitamin D or parathyroid abnormalities) plus poor or excessive calcium intake may be enough to cause symptomatic imbalances, however.
Currently, an estimated 72% of calcium in an average American's diet comes from dairy foods. Vegetables (7%), grains (5%), legumes (4%), and meat/fish (3%) also contribute to total calcium intake. Although fortified foods, including cereals, juices, and non-dairy milks are widely available and utilized, it is not currently known how much they contribute to dietary calcium nationwide.
According to the 2010 USDA Dietary Guidelines for Americans, people older than 9 years old have 3 cups of milk per day. This would provide nearly 900 mg of calcium; assuming that some calcium comes from other foods, this would likely be enough calcium for most people.
However, many people by choice or medical need avoid dairy in their diet. For those who do not follow a vegan diet, canned sardines or salmon may be an easy way to replace a large portion of dairy calcium. Tofu, bok choy, and turnip greens are examples of good vegan calcium sources.
Calcium can be a relatively difficult mineral to absorb from foods. Depending on the type of calcium, and more importantly other accessory nutrients present in the meal, calcium absorption can vary greater than ten-fold from food to food.
The most important contributors to this variability are the two nutrients (sometimes referred to as anti-nutrients) phytate and oxalate. Both are able to bind calcium tightly, reducing its absorption. Both are also nearly exclusively found in plant foods, with much variation from source to source.
In a practical sense, this means that having foods rich in phytate and oxalate at the same time as your best calcium sources may interfere with absorption. But to put this point in perspective, people who eat largely plant based diets (i.e., vegetarians) do not have increased risk of osteoporosis, which you would predict if these plant-based nutrients were impairing calcium absorption to a clinically relevant degree. So, while you do not absorb calcium as efficiently from non-dairy foods, this does not make them irrelevant or counter-productive. We recommend several servings of calcium-rich vegetables throughout the day to maximize availability of this nutrient.
As described earlier, many processed food manufacturers add calcium to packaged foods including non-dairy milks, fruit juices, grain-based cereals, and other products. We do not recommend that you rely on these calcium-fortified foods to meet your calcium needs. For more details about fortification of foods with calcium, please see our section Impact of Cooking, Storage and Processing.
|World's Healthiest Foods ranked as quality sources of|
|Collard Greens||1 cup||62.7||267.90||27||7.7||excellent|
|Turnip Greens||1 cup||28.8||197.28||20||12.3||excellent|
|Mustard Greens||1 cup||36.4||165.20||17||8.2||excellent|
|Beet Greens||1 cup||38.9||164.16||16||7.6||excellent|
|Bok Choy||1 cup||20.4||158.10||16||14.0||excellent|
|Yogurt||1 cup||149.4||296.45||30||3.6||very good|
|Swiss Chard||1 cup||35.0||101.50||10||5.2||very good|
|Kale||1 cup||36.4||93.60||9||4.6||very good|
|Cinnamon||2 tsp||12.8||52.10||5||7.3||very good|
|Sesame Seeds||0.25 cup||206.3||351.00||35||3.1||good|
|Cow's milk||4 oz||74.4||137.86||14||3.3||good|
|Brussels Sprouts||1 cup||56.2||56.16||6||1.8||good|
|Green Beans||1 cup||43.8||55.00||6||2.3||good|
|Summer Squash||1 cup||36.0||48.60||5||2.4||good|
|Romaine Lettuce||2 cups||16.0||31.02||3||3.5||good|
|Black Pepper||2 tsp||14.6||25.69||3||3.2||good|
Density>=7.6 AND DRI/DV>=10%
Density>=3.4 AND DRI/DV>=5%
Density>=1.5 AND DRI/DV>=2.5%
Calcium content of foods is remarkably stable. Calcium does not degrade or leech out of foods as they are stored, and there does not appear to be any major change in bioavailability of calcium over the shelf life of the best food sources.
Some calcium-containing foods also contain two substances that have a long history of controversy in scientific research - oxalic acid and phytic acid. (These substances can also be referred to as "oxalates" and "phytates.") Both oxalates and phytates can bind together with calcium and other minerals, and this binding process shows up in some studies as lowering the amount of calcium that gets absorbed from our digestive tract up into our body. However, our digestive processes are never simple, and other studies show people to be fully healthy in terms of their calcium nourishment even when their overall meal plan contains many foods high in oxalates and phytates.
As a general rule, we do not think that you need to avoid oxalate or phytate-containing foods in your meal plan even if your primary goal is to improve your calcium intake. Boiling a high-oxalate food like spinach can often reduce its oxalate content by about 10%. This result may be a good thing if you are focusing on calcium nourishment, but once again, we do not think that this issue should be treated as a key factor in your decision-making process about your meal plan or consumption of raw versus cooked spinach.
Phytates in food are often reduced by sprouting, and if you enjoy sprouted seeds, beans, nuts, legumes or grains, you may get some improved mineral nourishment (including calcium nourishment) from these foods in sprouted versus non-sprouted form. Fermenting can also lower a food's phytate content, particularly if the bacteria and other micro-organisms used in fermentation contain phytase enzymes that can break down phytates. For this reason, you may get some increased calcium benefits from consumption of calcium-containing, traditionally fermented foods including Tofu, Yogurt, grass-fed and sauerkraut.
Note that if you simply look at food charts of calcium content, it may look like cooking foods increases calcium levels. This is just an artifact, however, an only reflects the loss of water content, which in turn concentrates the same amount of calcium in a smaller volume.
Many processed foods add calcium in the manufacturing process. Some undergo a process called fortification, or the adding of calcium salts that were not originally there. Non-dairy milks, juices, and breakfast cereals all are commonly fortified with calcium.
Another specific example of calcium being added in the processing of food is in the manufacture of tofu. Many tofu products use calcium sulfate to precipitate the solid protein-rich soy as curds from solution. Other tofu products use sodium (referred to as nigari) to coagulate the solid product. Choosing tofu made with calcium sulfate comes close to doubling the amount of available calcium per serving.
Unlike most other nutrients where deficiency is defined by an amount below which a deficiency syndrome emerges, calcium deficiency has been defined as an intake amount below that required to prevent net daily calcium loss. For most adults, this amount is 300-400 milligram of absorbable calcium per day. Because dairy calcium is absorbed at about 30% of total calcium (with most vegetable sources close behind in the low-to-mid-20% range), this means that amounts around 900-1,200 milligram per day are enough to offset the daily loss of this mineral.
Because children and adolescents are actively depositing new bone at a rapid clip, just getting enough calcium to offset losses is not enough. Depending on the age of the child, up to an extra 400 mg of dietary calcium may be necessary to keep up with bone growth. See the section on public health recommendations below for age specific intake recommendations.
Absorption of dietary calcium becomes progressively less efficient with age, and we absorb about 0.2% less per year after age 40. This may not sound like much, by the time we reach our 60s and 70s, this small and incremental change is large enough that our daily calcium requirement needs to increase. Given that this is also an age range where bone mineral density loss can occur quickly, calcium nutrition is arguably nearly as important in the post-menopausal and elderly populations as it is in children and adolescents.
Americans very frequently fail to get the daily recommended intake of calcium. Women, in particular, fail to achieve the Recommended Dietary Allowance (RDA) on average in every age group older than 8 years old. Less than 15% of adolescent girls and less than 10% of elderly women (the populations who should be most careful about calcium nutrition) meet daily requirement thresholds through their diets.
People who don't regularly consume dairy products are the most likely to have the most difficulty achieving a positive calcium status; this may because the average U.S. adult doesn't routinely eat foods like fresh greens and tofu, which are also concentrated calcium sources. The average American gets about 1.8 cups of the recommended 3 cups of dairy products per day, but there is a great deal of individual variability in this intake estimate.
Generally speaking, moving from a standard American processed food diet toward the World's Healthiest Foods style of eating will spread out your calcium intake among a wide variety of foods that contain a moderate amount of calcium, rather than relying exclusively on the frequent intake of dairy products to meet your needs.
Even if your diet contains enough calcium by the DRI standard, it is still possible to be in calcium deficit, as many factors control calcium absorption, deposition, and excretion. These factors would be those that can be identified by a healthcare practitioner. By paying attention to these factors, it may be possible to affect your net calcium balance by keeping the mineral around longer, as well as maintaining plenty of daily supply.
One of the biggest contributors to calcium nutrition is vitamin D. Low levels of vitamin D can impair absorption of calcium from the intestines. Secondarily, low levels of vitamin D can impair the ability of the kidneys and bone to maintain normal circulating calcium levels. Because dietary vitamin D levels tend to be low in the population, this ends up being a potential amplifier of problems related to low calcium intake.
Many foods that contain calcium also contain vitamin D. For example, two of our top calcium-containing WHFoods (sardines and cow's milk) also belong to our top vitamin D-containing WHFoods. This overlap between calcium and vitamin D in whole, natural foods is a good thing, and it's no accident. These two nutrients clearly work together in metabolism. For example, as described earlier, vitamin D is needed to move calcium from our digestive tract up into our body. Because the balance of calcium and vitamin D in whole, natural foods is a healthy one, it's best to rely on these foods as your source for both nutrients, and there is no need for you to worry about your calcium and vitamin D balance if you are following a meal plan that is primarily composed of whole, natural foods.
However, very high dose supplementation with either calcium, vitamin D, or both may result in a balance for these two nutrients that is not optimal. If you are taking daily vitamin D supplements well above the Tolerable Upper Limit for vitamin D as set by the National Academy of Sciences at 4,000IU for adults, and/or calcium supplements well above the Tolerable Upper Limit for adults ranging from 2,000-3,000 mg, we recommend that you talk with your healthcare provider about the best supplementation plan to follow, so that you can be sure to get an optimal and safe ratio of these two nutrients.
Calcium can compete with many other minerals for absorption, most importantly magnesium, zinc, and iron. At dietary intakes of up to 1,500 mg per day, however, this interaction does not appear to be clinically important. If you routinely eat more than 1,500 mg of dietary calcium per day, you may need to increase your daily iron and zinc supply accordingly.
Diets high in sodium increase the loss of calcium in the urine. At DRI intakes and above of calcium, a goal most Americans fail to achieve, our kidneys are believed to be able to offset this calcium loss and maintain bone density. Since DRI values are based in part upon managing dietary intake to offset urinary loss, this should not be a surprise. What is not currently known is whether keeping dietary sodium under control—average Americans get more than double the recommended amount of sodium daily—would allow for calcium balance at a smaller average intake of calcium than the DRI.
The size of the effect of reducing dietary sodium on bone loss is not just an academic concern. The sample menus on our site range between 1,100 and 2,400 mg of sodium per day, whereas standard American diets average between 4,000 and 5,000 mg per day. Reducing dietary sodium in this way would be expected to keep an extra 20 or so mg of extra calcium in the bones each day.
Dietary protein has a complex relationship with calcium balance. On the positive side, diets high in protein increase stomach acid production, potentially optimizing intestinal absorption of calcium. On the other hand, dietary protein also increases the loss of calcium in the urine. At dietary protein intakes that most Americans achieve, these countervailing forces very likely balance each other out, leaving no overall effect. At extremes of protein intake, particularly protein calorie malnutrition, calcium balance can be disturbed.
Alcohol leads to modest loss of calcium in the urine, which is marginal for most adults. For example, giving adult men a daily alcohol dose equivalent to just over four shots of liquor was not associated with significant change in urine calcium loss. Long-term alcohol abuse, however, is a risk factor for bone loss, likely by a mechanism that involves the hormones that control calcium blood levels.
Even though the phytate found in plant foods may impair calcium absorption, it does not appear that diets high in phytate associate with loss of bone density. In fact, the opposite is true—diets high in phytate have been associated with improvements in bone mineral density. This is good news since plant-based eating plans like those featured here are rich in phytic acid. While noting that some other sources disagree—particularly advocates of the paleolithic diet strategies—we do not recommend restricting phytate-rich foods to improve calcium absorption under any circumstances.
The National Academy of Sciences (NAS) in its 2010 public health recommendations for calcium noted that excessive amounts of dietary calcium are "difficult, not impossible" to achieve in normal healthy adults. In a nation where as many as 90% of at-risk demographic groups (e.g., adolescents, elderly women) fail to reach target intakes of calcium, worrying about calcium excess seems like a misplaced effort to us.
However, to get a better understanding in this area, let's take the NAS guidelines for calcium and see what level of food intake would constitute too much. In its 2010 public health recommendations for calcium, the NAS established the following maximum recommended amounts (which they call Tolerable Upper Intake Levels, or ULs) for this mineral:
Tolerable Upper Intake Levels (ULs) for Calcium:
In order for a middle-aged person to exceed this 2,500 milligram limit on calcium intake, that person would need to eat about 10 cups of spinach or collard greens (two of our "excellent" WHFoods sources of calcium). Similarly, a person would need to consume about 6 cups of yogurt to go over this amount.
There is a condition called milk-alkali syndrome where serious dehydration can occur related to excessive calcium intake. This is almost always caused by supplements of calcium (or antacids medications containing calcium), although it is known to be a risk at intake of dietary calcium above 2,000 mg per day. . As noted earlier, however, intake of 2,000 milligrams from a day's food is generally unlikely. Persons with existing kidney-related problems or special risk of such problems fall into a special category here. Under these circumstances, we recommend consultation with a healthcare provider to determine the ideal maximum amount of dietary calcium.
Because we have such elaborate hormonal control of our calcium levels, it is much more likely that calcium excess events are due to a medical condition than due to eating too many calcium-rich foods.
In 2010, the National Academy of Sciences released Dietary Reference Intake (DRI) updates that included Recommended Dietary Allowances (RDA) for age and gender specific calcium intake goals. These RDAs are as follows.
The upper limit (UL) of calcium according to the DRI recommendations varies by age and gender. They are as follows.
Please note that as we cited above, it is nearly impossible to reach this amount of calcium without heavily leaning on supplements or fortified foods.
The Dietary Reference Intake (DRI) for calcium as established by the National Academy of Sciences for 19-50 year-old women is 1,000 milligrams, and that is the amount we chose as our WHFoods standard. In this particular case, 1,000 milligrams is also the Daily Value (DV) established by the U.S. Food and Drug Administration (FDA).