Mention the word calcium, and the first thing that comes to mind is ‘bones,’ or perhaps ‘teeth.’ That makes sense, since 99 percent of all calcium stored in the body is in the bones. Teeth contain a large percentage of calcium, too, but unlike what happens with bones, once calcium enters teeth, it stays there. The other 1 percent of calcium flows in the blood, and the body maintains a tight control over the precise level of blood calcium for good reasons. While the percentage of calcium found outside of bone may seem small, it participates in a number of functions essential to life.
Without a doubt the best food sources of calcium are dairy foods, especially milk. That could be a problem for some bodybuilders, who harbor the notion that milk is a fattening food that obscures muscular definition. The same holds true for other reliable calcium-rich dairy foods, such as cheese and yogurt. As a result, many bodybuilders avoid eating any type of dairy food.
Then there’s the possibility of taking in too much calcium, especially for men, simply because they eat more calories and may be exposed to a greater number of calcium sources, including food supplements. Too much calcium is associated with such problems as a loss of protein, inhibition of the absorption of other minerals and, possibly, kidney stones. The question is, Are those side effects actually possible?
The Myriad Effects of Calcium
Calcium is an essential mineral. Perhaps it is most often linked to preventing osteoporosis in women. Osteoporosis is a bone-wasting disease that begins at about age 30 if calcium intake is limited. As women age, their estrogen levels drop, which further adds to the detrimental effect of a lack of calcium, since estrogen also helps maintain bone structure. Studies show that 28 million Americans, mostly women and older men, are affected by osteoporosis. Having osteoporosis increases the risk of hip fractures in older people, and 20 percent of those hip-fracture victims die from the complications of subsequent surgery.
As noted, teeth are calcified tissue. Besides calcium, teeth require phosphorus, protein, fluoride and vitamins A and C for proper development. When you don’t get enough calcium from food sources, your body leaches calcium from bones to maintain the narrow range of required blood calcium levels. The body will not remove calcium from teeth, but it will gradually remove calcium from supporting jawbone structures, leading to a loss of teeth.
The blood calcium must be maintained at a minimal level to function in a number of processes, such as the following:
‘ Muscular contraction and relaxation, including heart muscle
‘ Blood coagulation
‘ Nerve transmission
‘ Enzyme activation
‘ Hormone stimulation
‘ Maintenance of intracellular structural integrity
The body places maintenance of blood calcium levels at top priority. When you don’t get enough calcium from food, the body adjusts in a number of ways. The kidneys begin to conserve calcium and excrete less. Calcium absorption is upgraded. Then the body withdraws calcium from its ‘bank,’ the bones. Chemical signals are sent that result in a release of parathyroid hormone (PTH), which leads to a decrease in urinary calcium excretion coupled with a mobilization of calcium from bone. Release of PTH, in turn, promotes the release of calcitriol, the activated hormone form of vitamin D. Calcitriol increases intestinal calcium absorption while helping to limit calcium excretion. As the calcium levels begin to rise in blood, calcitonin, a hormone synthesized in the thyroid, is released. It blocks the release of calcium from bone to prevent too much calcium from entering the blood.
When the body detects a lack of adequate calcium intake and reacts by releasing calcitriol, the calcitriol promotes a number of undesirable side effects. Due to its potent effect of promoting calcium entry into cells, calcitriol tends to upgrade muscular contraction. When that happens in the smooth muscle that lines blood arteries, higher blood pressure can result. People who are sodium sensitive react most strongly to that calcium-calcitriol effect.
Other studies show that calcium may help alleviate the monthly mood disturbances that women may experience as a result of the hormonal effects collectively known as premenstrual syndrome, or PMS. Some of the typical symptoms of PMS, such as cramping, irritability and depression, are also known to occur during a calcium deficiency.
Colon cancer is the number-three cause of cancer deaths in the United States. Studies show that calcium may help prevent it through several possible mechanisms. An intake of dietary fat increases the level of free fatty acids and bile in the intestine, which may irritate the cells lining the intestine, leading to mutagenic changes that result in cancer. Calcium helps by binding to the fatty acids and bile, forming an insoluble soap, which is less irritating to colonic cells. One study found that colon cancer was reduced by 75 percent in men who took in 1,200 milligrams of calcium daily, and by 50 percent when they took more than 150 units of vitamin D, which aids calcium absorption.1
Calcium may also help prevent colon cancer by lowering the number of intestinal polyps, which are precursors of colon cancer. A study from Texas showed that taking more than 1,300 milligrams of calcium a day helped reduce such polyps.
A recent study found that women who get more calcium, lowfat milk and lactose, or milk sugar, show a reduced risk of ovarian cancer.2 On the other hand, an 11-year study of 20,885 men found that those taking in more than 600 milligrams of calcium daily had an increased risk of prostate cancer.3 That is troubling until you read the actual study, which reveals that the increased risk of prostate cancer among the subjects didn’t result directly from calcium but instead from a lack of vitamin D, specifically calcitriol, which appears to offer protection against prostate cancer. As noted above, calcitriol release is suppressed by calcium ingestion.
In the past people who had a tendency to make kidney stones were often advised to avoid a high calcium intake. The basis of that recommendation was the fact that the most common type of kidney stone is composed of calcium and oxalate, a common ingredient in many vegetables. Newer research, however, shows an opposite effect: Too little calcium promotes kidney-stone formation. The studies show that calcium locks on to oxalate, decreasing its entry into urine. While some people have a genetic abnormality’called absorptive hypercalciuria’that leads to an elevated absorption of calcium and must limit their calcium intake, people who don’t have that condition can take in up to 2,500 milligrams of calcium daily with no increased incidence of kidney stones.
The most recent research about calcium shows that it may help prevent bodyfat accumulation, an effect I discuss below.
One reason dairy foods are by far the best natural food sources of calcium is the superior absorbability of the calcium they contain. While calcium does exist in other foods, components in those foods, such as oxalate, tend to inhibit calcium absorption and uptake. For example, the calcium found in spinach is absorbed at a low rate due to spinach’s high oxalate content. The calcium in navy, pinto and red beans is absorbed at half the rate of that found in milk. Calcium from milk is highly absorbable because of other factors, such as lactose, phosphopeptides and amino acids; however, one study showed that contrary to popular belief, lactose does not increase calcium absorption in lactose-tolerant adults.4
Efficient calcium absorption also requires the presence of vitamin D. Vitamin D is actually a pro-hormone, since it’s converted into its active, hormonal form, calcitriol, in the kidneys. Calcitriol regulates intestinal calcium uptake. When a body lacks vitamin D, it absorbs less than 10 percent of ingested calcium, compared to the usual 30 percent. The effect of low vitamin D is increased in women who have low estrogen levels. Vitamin D can be synthesized when skin is exposed to sunlight, but that depends on many factors. Exposing the face, arms and hands to sunlight for five to 15 minutes, two to three times a week, may do the trick. If you’re getting Vitamin D from food or supplement sources, the suggested dose is 200 units a day for those aged 50 and under, 400 units for those over 50 and 600 units for those over 70.
Older studies showed that some forms of dietary fiber can interfere with calcium absorption, but more recent research indicates that the effect is negligible. On the other hand, elements found naturally in many whole grains and vegetables, such as oxalate and phytate, can reduce the calcium uptake from food. As mentioned earlier, you can only absorb about 5 percent of the calcium found in spinach due to its high oxalate content, while the absorption rate of the calcium in milk is 30 percent. Interestingly, chocolate milk contains small amounts of oxalate yet doesn’t seem to interfere with calcium absorption.
Calcium is closely related to another mineral, phosphorus, which is widely found in many foods. Previously, many scientists believed that the greater availability of phosphorus in food compared to calcium created an imbalance in the ratio of phosphorus to calcium, leading to increased calcium excretion. More recent studies, however, show little or no effect of phosphorus as typically consumed by most people on calcium metabolism. In fact, the phosphorus content of high-protein foods, such as meat, is thought to prevent the excessive excretion of calcium that may occur with purified protein sources.
That aspect is underscored by a study published in 2002.5 It examined the calcium, phosphorus and protein interrelationships in 191 nuns and found no relationship between calcium absorption and phosphorus or protein intake.
Another study looked at the effects of eating more meat on calcium absorption.6 It featured low, moderate and high intakes of calcium and found that meat intake didn’t affect calcium metabolism at any level.
Scientists believe a high-protein diet leads to increased calcium excretion because of the higher level of acidity that results from the metabolism of certain amino acids that are the constituents of protein. The body releases calcium to act as a buffer for such increased acidity, but one study shows that simply by eating alkaline foods, such as fruits and vegetables, you can totally block this acid-based loss of calcium.7
In fact, emerging research shows an opposite effect: Too little protein intake results in increased calcium excretion.8 The mechanism is an increased release of PTH due to a lack of protein.
One element that does lead to increased calcium excretion is sodium. Every 2,300 milligrams of sodium excreted by the kidneys increases urinary calcium by 20 to 60 milligrams. Eating excess sodium increases the requirement for calcium. Conversely, extra calcium will help rid the body of excess sodium and consequent water retention. That effect plays a role in how calcium helps lower blood pressure in sodium-sensitive people. Calcium also has an inverse relationship with lead, a toxic mineral. The body absorbs less lead when it’s taken in with calcium. That’s significant because many natural calcium supplements, such as bone meal and dolomite, may contain lead.
Some of the natural protein peptides found in milk proteins also promote calcium uptake. Examples are the casein phosphopeptides that are formed during the enzymatic digestion of casein milk protein.9 A probiotic called fructooligosaccharides likewise promotes calcium absorption.10 Those who refuse to eat the most reliable food source of calcium’dairy products’often rely on calcium supplements. Many such supplements present notable problems, however. One study that examined the absorption characteristics of 37 different calcium supplements found that only five were absorbed. If you take in large doses of isolated calcium supplements, you can experience such side effects as constipation, bloating and intestinal gas.
One popular calcium supplement, calcium carbonate, which is chalk, can interfere with iron uptake if you take them in at the same time. That type of calcium is best taken with meals, since it requires a certain level of acid for absorption. Still, even people with normal stomach acidity absorb only about 22 percent of a calcium carbonate supplement. As noted above, some natural forms of calcium supplements, such as dolomite, bone meal and oyster shell, may contain such contaminants as lead, aluminum, arsenic, mercury and cadmium, all of which are toxic metals; however, most commercial calcium supplements are tested for the presence of such contaminants.
Women are often advised to take at least one dose of calcium at night, since calcium loss from bone increases at night, but a recent study found that it made little difference whether subjects took calcium supplements at night or early in the day.11 Calcium is, however, better absorbed when taken in doses of no larger than 500 milligrams.
Another issue involves the best supplemental form of calcium. As noted, most forms of calcium require some acid release, relegating their optimal intake to meals. One form, calcium citrate, does not require acid release and can be taken at any time. That’s the form often suggested for older people, many of whom lack sufficient gastric acidity. According to a recent study that examined this issue, though, it makes little difference whether you get your calcium from cheaper sources such as calcium carbonate or the more expensive citrate form.12
The most soluble supplemental forms of calcium are calcium citrate malate, which is 10 times more soluble than calcium citrate, and calcium bis-glycinate, which is a whopping 205 times more soluble than the citrate form. They’re suggested for people who experience side effects from lack of complete absorption of other calcium supplements.
Can you take in too much calcium? Excess calcium interferes with the absorption of other minerals, including magnesium, phosphorus, iron and zinc. Boron, which is found in fruits, helps to retain ingested calcium when taken in doses of two to three milligrams daily. Excess calcium is defined as an intake of more than 2,500 milligrams a day. Excessive calcium can lead to kidney failure, calcium deposits in soft tissue, irritability, headaches and other symptoms, but keep in mind that even under the most favorable circumstances, you absorb only about 30 percent of all the calcium you take in any form.
An important consideration about calcium supplements is their elemental content, which refers to the true calcium content. For example, calcium carbonate contains about 40 percent elemental calcium. The citrate and bis-glycinate forms contain an average of 20 percent actual calcium. Most supplement labels reflect those values and indicate the elemental levels of available calcium.
A condition known as milk-alkali syndrome results from the concurrent ingestion of alkaline substances, such as baking soda, and calcium, leading to dangerously high levels of calcium in the body. Even so, such conditions are usually brought on by intakes in the range of 2,500 to 16,500 milligrams of calcium a day. In contrast, only 21 percent of people meet the minimal suggested level of calcium.
The Calcium/Bodyfat Connection
Recent studies show that calcium may help control bodyfat levels. That relates to the increased release of calcitriol. When secreted in excess, calcitriol promotes the influx of calcium into fat cells, leading to an increase in the activity of fat cell enzymes that promote increased fat synthesis, while other enzymes that promote fat losses are inhibited. Calcium intake suppresses calcitriol release.
One study found that people on diets that included dairy products lost 70 percent more weight than those who didn’t eat any dairy foods. Those in the dairy group also lost 64 percent more fat than the nondairy group. Increasing dairy foods also promotes the activity of uncoupling protein-2, a cellular protein that promotes thermogenesis, or loss of fat calories as heat.
A two-year study of exercising women, aged 18 to 31, found that those who ate more dairy products gained less weight and bodyfat.13 It found that the calcium contained in dairy foods seemed to produce better results than straight calcium supplements, perhaps because of other elements contained in dairy foods that may be synergistic with calcium in promoting fat losses, such as conjugated linoleic acid (CLA).
In fact, studies show that dietary calcium sources such as milk are twice as effective as pure calcium supplements in promoting fat losses. According to researcher Michael Zemel of the University of Tennessee, milk may provide better effects for fat loss because of naturally occurring elements found in it. One such element is a native milk protein that somewhat inhibits angiotensin-converting-enzyme activity. That’s significant because angiotensin-2 may play a role in promoting increased bodyfat synthesis.14
People who just don’t want to take calcium pills can get additional calcium and other nutrients related to its uptake in a quality meal-replacement supplement. That’s especially advantageous to those seeking fat loss, since meal replacements are usually low in both carbohydrates and fat. A study of obese people in Wisconsin showed that when the subjects used a meal-replacement supplement, they increased their calcium intake by 30 percent and doubled their vitamin D intake. On days when they didn’t eat the meal replacement, they got only 40 percent of the recommended daily value of 1,000 milligrams of calcium.15
Zemel and other calcium researchers are quick to point out that taking in calcium alone will not result in a significant loss of bodyfat. You still need to exercise and lower your calories. Not getting enough calcium, however, will likely inhibit efficient fat loss. A prudent intake of calcium is about 1,500 milligrams a day. Note that the best way to accomplish that is by heeding the factors that influence calcium metabolism discussed above.
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2 Goodman, M.T., et al. (2002). Association of dairy products, lactose, and calcium with the risk of ovarian cancer. Am J Epidemiol. 156:148-57.
3 Chan, J.M., et al. (2001). Dairy products, calcium, and prostate cancer risk in the physician’s health study. Am J Clin Nutr. 74:549-54.
4 Zittermann, A., et al. (2000). Lactose does not enhance calcium bioavailability in lactose-tolerant, healthy adults. Am J Clin Nutr. 71:931-36.
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6 Spencer, H., et al. (1978). Effect of a high protein (meat) intake on calcium metabolism in man. Am J Clin Nutr. 31:2167-2180.
7 Barzer, U.S., et al. (1998). Excess dietary protein can adversely affect bone. J Nutr. 128:1051-53.
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9 Ferraretto, A., et al. (2001). Casein phosphopeptides influence calcium uptake by cultured human intestinal HT-29 tumor cells. J Nutr. 131:1655-1661.
10 Morohashi, T., et al. (1998). True calcium absorption in the intestine is enhanced by fructooligosaccharide feeding in rats. J Nutr. 128:1815-1818.
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17 Zittermann, A., et al. (2000). Exercise-trained young men have higher calcium absorption rates and plasma calcitriol levels compared with age-matched controls. Calcif Tissue Int. 67:215-219.
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