May 1, 1998

22 Min Read
Boning Up on  Calcium Fortification

Boning Up on
Calcium Fortification
May 1998 -- Applications

By: Lynn A. Kuntz

  As time marches on, we all may be in danger of singing a new version of the old folk song, "Them bones, them bones, them brittle bones..." Luckily, one of the most obvious nutrition/health links is calcium intake and osteoporosis prevention. This has fueled a high level of interest in calcium fortification among food processors as well as consumers.

The calcium connection

    Calcium is the most abundant mineral in the human body. Most calcium, approximately 99% of the total, can be found in the skeleton and teeth; the rest is in blood and body fluids. The most obvious benefit of calcium consumption is the aforementioned link to bone health as we age.

  Children require calcium for proper skeletal growth and development. But when growth stops, the need for calcium does not. Into to the mid-30s, the body builds peak bone mass, its maximum bone strength. The higher this level, the less likely problems will develop later in life. Even after peak bone mass has been attained, calcium is still required to maintain strong, healthy bones. With age, both men and women lose calcium from the skeleton. However, the rate of loss in women is typically double that of men and is linked to the slowdown in estrogen production. For either gender, the result of diminished bone mass is osteoporosis.

  Osteoporosis is a disease characterized by bone loss and skeletal deterioration, leading to bone fragility and increased risk of fractures. It is defined as approximately 25% reduction in bone mass compared to a healthy young adult. Although considered a disease of the elderly, osteoporosis often begins early in life, long before symptoms occur. According to the National Osteoporosis Foundation, 28 million people are affected by osteoporosis, and that number may rise to 41 million by 2015.

  Along with combating osteoporosis, calcium is essential for: muscle function regulation, including normal heartbeat and muscle contraction; blood clotting; hormone regulation, including insulin; and enzyme activation. In addition, low calcium intake has been implicated in preeclampsia and several other diseases, including colon cancer and hypertension. At this time, however, medical experts have insufficient data to make a definitive link between increased calcium consumption and the prevention of these diseases.

On the level

    FDA has established a Daily Value (DV) of calcium at 1,000 mg/day for adults and children older than age 4. However, last August, the Institute of Medicine, part of the National Academy of Sciences, Washington, D.C., issued the first in a series of reports on Daily Reference Intakes (DRI), with recommendations to update the Recommended Dietary Allowances (RDA) for calcium and several other important nutrients.

  The DRI for calcium and the other nutrients reflects current research on chronic-disease prevention, rather than the minimum amount needed to prevent a nutritional deficiency (the benchmark used for the old RDAs). The DRIs consist of four categories: RDA, Estimated Average Requirement, Adequate Intake, and Tolerable Upper Intake Level. The daily Adequate Intake recommendations for calcium are listed in the table, but the most notable changes are the recommendations for children ages 9 to 18 (1,300 mg) and adults, ages 51 and older (1,200 mg). The tolerable upper intake level, which sets a maximum amount "that is unlikely to pose risks of adverse health benefits to almost all individuals in the target group," was set at 2,500 mg/day for calcium. The full report can be found in Dietary Reference Intakes: Calcium, Phosphorous, Magnesium, Vitamin D and Fluoride, by the Standing Committee of Dietary Reference Intakes, Food and Nutrition Board, Institute of Medicine (1997, National Academy Press, Washington, D.C.).

  The National Osteoporosis Foundation estimates that the average adult gets between 500 and 700 mg of calcium daily. According to a 1995 survey by the U.S. Department of Agriculture, girls and young women ages 12 to 19 consumed only 777 mg calcium daily. Part of the shortage in calcium intake has been attributed to a drop in dairy product consumption, particularly milk drinking. A USDA study comparing 1994 daily beverage intakes with those in the late 1970s found that children and teenagers are drinking less milk and replacing it with other drinks. Among teenagers in the survey, those considered milk drinkers dropped from three-fourths to little more than half. Two to three times more children and teenagers drank non-citrus fruit juices. The consumption of soft drinks by teenage boys nearly tripled.

    In addition, negative publicity associating dairy products with high fat levels also may have lowered the U.S. population's calcium intake. In 1994, an average of 25.9 gallons of milk each per year were consumed by 6 to 12 year olds, according to figures from Dairy Management, Inc., Rosemont, IL. Those in the 13- to 34-year-old range consumed 17.9 gallons per year. The declining milk consumption continued with age - those older than 60 consume only 9.5 gallons of milk annually.

Oughta be a law

    These figures appear to leave the door wide open for the development of calcium-fortified foods. As usual, the government has stepped in and hung a few signs on that door.

  First of all, according to 21CFR104, FDA "does not encourage indiscriminate addition of nutrients to foods, not does it consider it appropriate to fortify fresh produce; meat, poultry or fish products; sugars; snack foods such as candies or carbonated beverages." However, the same section states that a listed nutrient (including calcium) "may be appropriately added to a food to correct a dietary insufficiency recognized by the scientific community to exist and known to result in nutritional deficiency disease..." So, depending on a company's interpretation, a wide variety of products might be calcium-fortified.

  Once the decision to fortify is made, the government does provide some labeling options. The first is in the Nutrition Facts panel. Calcium is allowed to appear on the nutrient list. However, if it is present in amounts less than 2% of the RDI, label declaration is not required if the following statement is placed at the bottom of the table of nutrient values: "Not a significant source of calcium" (or "other nutrients" if that statement qualifies).

  FDA also allows several terms for foods containing higher levels of calcium. Products with 10% DV calcium or more added can include the following: "Calcium-Enriched," "Calcium-Fortified" or "More Calcium." Products ranging between 10% to 19% DV calcium may include these statements: "Contains Calcium," "Provides Calcium" or "Good Source of Calcium." Finally, products with 20% DV calcium or more can carry the claims: "High in Calcium," "Rich in Calcium" or "Excellent Source of Calcium."

  Products with a small serving size can be especially problematic. "For a 10% claim, you need 100 mg of calcium, and that's difficult for something like confectionery products where the serving size is only 20 grams or 40 grams," says Barbara van Mossevelde, technical service representative, Purac America, Inc., Lincolnshire, IL. "Not that many products are fortified below that level - it only allows you to remove that zero. But, for some products, that may be enough."

  The food label can carry a claim linking calcium consumption and prevention of osteoporosis. However, a food must contain 20% or more of the DV for calcium (200 mg) per serving; have a calcium content that equals or exceeds the food's content of phosphorus; and contain a calcium form that the body can readily absorb and use. The claim must name the target group most in need of adequate calcium intakes (teens, and young adult white and Asian women) and state the need for exercise and a healthy diet. A product with 40% or more of the calcium DV must state on the label that a total dietary intake greater than 200% of the Daily Value for calcium (2,000 mg or more) has no further known benefit.

    "In developing any application, the serving size and desired percentage of the RDI are critical parameters," says Charles King, technical marketing manager, Glucona America, Janesville, WI. "Most fortification loadings range from 10% of the RDI per serving, which is required to make a calcium claim, to 30% per serving, which is the level in milk."

Ingredient roster

    Food technologists wanting to design products with significant levels of calcium can first start with common foods and ingredients that contain calcium. The most obvious choice is dairy products, which contain approximately 250 to 300 mg calcium/8 oz. milk. But other foods also can provide significant levels of calcium: canned fish, such as tuna and salmon; grains, particularly lime-processed corn; some dark green vegetables, such as kale and broccoli; some legumes; calcium-set tofu; fruits, such as figs and kiwi; and seeds and nuts, including sesame seeds and almonds.

  Still, to achieve significant calcium levels in foods, most products will require a calcium salt or dairy calcium ingredient for fortification. Standard nonfat dry milk contains 1,300 mg calcium/100 grams; dry sweet whey contains 770 mg calcium/100 grams; and dry acid whey weighs in at 2,280 mg calcium/100 grams. In addition, many ingredient suppliers have developed specialized high-calcium dairy products with calcium contents ranging from 2% to approximately 25%.

  A wide variety of calcium salts are listed as GRAS (Generally Recognized as Safe). These include: calcium carbonate, calcium chloride, calcium citrate, calcium gluconate, calcium hydroxide, calcium lactate, calcium oxide and calcium phosphates (mono-, di- and tribasic-) - which are listed as general-purpose additives and are most commonly used for adding supplemental calcium to foods. Calcium glycerophosphate, calcium pantothenate, calcium pyrophosphate and calcium sulfate also are listed as GRAS, as nutritional or dietary supplements. In addition, Procter & Gamble, Cincinnati, has a patented calcium-delivery system, calcium citrate malate, that was originally used in the company's now-defunct Citrus Hill Plus Calcium drink.

  The high-calcium milk products take many forms. For example, New Zealand Milk Products (North America) Inc., Santa Rosa, CA, offers a High-Calcium Protein available in low-fat or nonfat forms made with either caseinates or total milk proteins. Calcium levels range from 2.7% to 15%, depending on the product. A patented process binds insoluble calcium carbonate to the protein, increasing the dispersability and suspendability of the mineral in aqueous systems. "If you are looking for protein fortification at the same time as calcium fortification, then you would want to use products with a lower calcium level to reach the proportion you're looking for in the finished product," says Lynn Kjeldsberg, food scientist, research and development, New Zealand Milk Products.

    Several products use dairy calcium. DMV International Nutritionals, the Netherlands, produces Lactoval Q/QM, a milk-mineral complex with only a low level of protein (1.0%), lactose (1.0%) and fat (0.4%) and 24.5% calcium. Davisco Foods International, Inc., Eden Prairie, MN, has developed a fractionated whey protein, VersaPRO, with 5% calcium and a high level of milk phospholipids. And, according to Stacey Goebel, technical sales manager for Avonmore Ingredients, Inc., Monroe, WI, the company will be introducing a product in July "in which milk minerals are isolated from dairy whey and will contain 26% calcium, 40% phosphorus as well as trace minerals."

On being bioavailable

    Any nutrient's effectiveness depends on how well the human body absorbs and utilizes it, or its bioavailability. The ultimate importance in food fortification of this complex topic is subject to debate, but bears consideration.

  Nutrition experts estimate that only about 25% to 35% of calcium in foods is absorbed. Several different factors influence this level, including the type of calcium, but it appears that one of the most important is the circumstances under which the calcium is consumed. Calcium absorption is reduced from foods containing high levels of oxalic acid, such as spinach, sweet potatoes, rhubarb and beans. The same holds true for those containing phytic acid, such as unleavened bread, raw beans, seeds, nuts, grains and soy isolates. Interestingly though, soybeans have large amounts of phytic acid, but they don't appear to significantly hamper calcium absorption. Some researchers speculate that phosphate might be related to decreased calcium absorption. Wheat bran appears to negatively affect calcium absorption, including that found in milk. Reduced calcium absorption or loss of bodily calcium also has been linked to high sodium, protein and caffeine intakes, although the nutritional implications of these studies are unclear at this time. Vitamin D might enhance the absorption of calcium since decreases in osteoporosis have been observed when the two are combined.

  On the other hand, studies show calcium negatively affects the amount of other minerals, notably zinc and iron, that the human body utilizes.

  Researchers have found that many of the components found in milk aid calcium's absorption, particularly lactose and magnesium. Milk also might prevent the precipitation of calcium in the presence of phytate according to a 1987 study by Platt, et. al. published in volume 52 of the Journal Of Food Science.

  According to Lex van Moorsel, product manager, technical sales support, DMV International, bioavailability of calcium depends on "a number of factors, including nutrient interactions - protein, sodium and dietary fiber - whether calcium is coingested with other foods, age, sex and calcium intake." Many of the bioavailability studies have been performed using calcium supplements. Dr. Robert Heaney, a researcher at Creighton University, Omaha, NE, has found that calcium absorption from supplements increases about 10% when taken with meals. The study showed increases in calcium absorption with calcium carbonate, calcium citrate, and milk when consumed with foods. (JAMA 1995;274:1012).

  Other studies by Heaney and other researchers using similar test conditions, combining a 250 mg calcium load using different compounds with a standardized meal, resulted in the following calcium absorption rates: citrate malate, 35%; milk, 29%; calcium carbonate, 27%; and tricalcium phosphate, 25%.

  "The problem with bioavailability is that you cannot give an absolute value of bioavailability of calcium from any one source because it's affected by so many factors," van Mossevelde says. "We've done studies that show that the matrix has a greater effect than the actual source used, but that on the average, calcium lactate shows a higher bioavailability than calcium citrate, gluconate, carbonate and phosphate."

  "It has been reported that dairy-derived minerals have better bioavailability and absorption characteristics than other calcium supplements," Goebel says. This is likely the result of the enhanced absorption promoted by lactose and minerals. In one rat study, conducted jointly with the American Institute of Baking, Davisco's VersaPRO had higher availability than calcium salts citrate, lactate and carbonate. Another factor that can promote calcium uptake is the presence of phospholipids, says Polly Olson, director of sales and marketing at Davisco. "Phospholipids are used to transport drugs across cell membranes, and the ability of phospholipids to transport calcium across the cell membranes is very well-documented," Olson says. "In VersaPRO, the phospholipid fraction is bound to the calcium and protein."

    However, the position of the National Institutes of Health is that the calcium level appears to have a greater impact on the calcium absorbed than a compound's bioavailability. FDA also doesn't make any distinctions regarding bioavailability of calcium additives. So, unless a compelling reason exists to focus exclusively on bioavailability, several other important factors come into play when choosing an ingredient for calcium supplementation.

Calcium characteristics

    First, the good news: Unlike many vitamins and minerals, calcium is fairly stable. Heat or oxidation won't change the calcium content. It also is not highly reactive in most cases, as are iron or copper. It won't present any toxicity issues at practical use levels.

  However, because the RDI and, therefore, the desired fortification level is very high, the ingredient used can have a significant impact on the finished product. The less calcium in the ingredient, the higher the level required to attain the target. The calcium content of calcium carbonate (40%) is higher than that of calcium phosphate (17% to 38%, depending on the form), calcium chloride (36%), calcium citrate (21%), calcium lactate (14%) or calcium gluconate (9%) on an equivalent weight basis.

  Flavor. Typically, calcium doesn't have an overwhelming effect on a fortified food's flavor, but in a bland system, certain flavors arise. Calcium lactate and calcium gluconate are considered to be the most bland of the calcium salts. Calcium carbonate may come across as soapy or lemon. Calcium citrate tastes acidic and the chloride salt may promote bitterness. Tricalcium phosphate has a bland flavor, but gives a gritty mouthfeel. Depending on the exact composition, dairy-based calcium ingredients may impart some notes associated with milk or milk proteins.

  "The higher the level - the smaller the serving size - the greater the impact you will have on flavor," says van Mossevelde. "If you are looking at an 8 oz. serving size with 50% RDI, that's difficult to do without any flavor impact. That's true even with the low-flavor calcium products. None are entirely tasteless."

  High levels of calcium, particularly insoluble forms, can produce a chalky mouthfeel often picked up as part of the flavor. They also promote astringency in the finished product. Large particle sizes of insoluble calcium salts might feel gritty in the mouth.

  Solubility. For ingredients used in many food formulations, particularly beverages and other liquid systems, solubility is of prime importance. Goebel reports that dairy-derived minerals have good solubility, and are stable in acid systems. Of the calcium salts, calcium lactate has the highest solubility at 25°C: 9.3 grams calcium per liter, followed by calcium gluconate (3.5 grams calcium per liter), calcium citrate (0.2 grams calcium per liter), and calcium phosphate and carbonate (less than 0.1 gram calcium per liter).

  Surprisingly, combining these salts might alter their solubility in an unexpected way. One commercial calcium-fortification product, GluconalÆ Cal (a combination of calcium lactate and gluconate) from Glucona America Inc., exhibits a solubility of 45 grams calcium per liter at 258C.

  "Soluble ones generally have a lower calcium content," notes van Mossevelde. "The insoluble forms have higher calcium, and tend to be less expensive. If you have a system where solubility is not an issue, it would make sense to use an insoluble one."

  The pH of the matrix greatly influences calcium solubility. A lower pH generally enhances solubility, while raising it can cause the solubility to drop. The higher the temperature, the higher the solubility.

  However, according to King, high solubility can have a downside. "Free calcium ions are in solution and available for reaction," he points out. "This has meant that complications in the form of calcium precipitates can develop if anions that give insoluble salts are present in the product. This primarily means free protein, and citric and tartaric anions. Such effects are promoted by temperature and time. Thus, although it is possible to add Gluconal Cal to milk at 10% RDA per 8 oz. serving, higher amounts are difficult to achieve without control of pH and addition of chelating agents." He also recommends lowering the pH of certain products with glucono-delta-lactone to reduce the level of available citrate ion to decrease the chance of precipitation in low-pH systems.

  Insoluble calcium also may precipitate out during processing. "That will increase the risk that not all of your product will contain the same level," warns van Mossevelde. "It may not allow you to meet your label claim."

  Finished product effects. Insoluble calcium may be dispersed in some systems, but dispersed calcium gives a product an opaque appearance. This can be a positive (such as when used in a low-fat dairy product) or a negative (as it would be in a clear juice drink in a glass bottle).

  Calcium may react with protein, particularly with heat, and cause sedimentation and gelation. Calcium can cause certain gums, such as alginates and pectin, to gel. In acidic mediums, below a pH of 3, calcium carbonate can react with the acid to form carbon dioxide, resulting in a foaming effect, according to Kjelsberg. "We saw that effect in a key lime pie formulation, and it was actually kind of interesting."

  Because many of the dairy-based calcium products contain significant levels of other ingredients, the added compounds affect the finished product to varying degrees. This is especially significant in the protein versions. The protein can increase water-binding or absorption, viscosity or gel-formation, emulsification and foaming. Again, depending on the desired characteristics of the finished product, this might turn out to be an advantage - or not. The functional properties of these ingredients can be controlled to a certain extent by modifying the process by, for example, using controlled denaturation to lessen their impact. Also, products containing lactose may not be the first choice for those considering lactose-free formulations.

    Label considerations. Since the way an ingredient appears on the label is often as important as what it does, this often impacts selection. In the case of calcium, the consumer might be more comfortable with the name of a dairy protein than a calcium salt. But kosher certification of non-dairy calcium salts might prove advantageous in other applications.

Pump it up

    "The Asian, and especially the Japanese, market is leading in terms of milk calcium in fortified products," says van Moorsel. "However, since calcium enrichment has become a worldwide trend, interest has arisen also from other geographical areas, including Europe and the U.S.A." The actual products that can be fortified with calcium are quite diverse, and can include dairy products, meal replacements, bakery products, soy milk and many other processed foods.

  Dairy products are often fortified with calcium. This may smack of bringing coals to Newcastle, but in reality, the declining dairy consumption and combined nutrition and complementary action of dairy products make this a good choice. If you take cottage cheese for example, one serving only has 69 mg of calcium (not all of which is absorbable). By adding a soluble calcium to the dressing, the liquid portion, this level can be increased substantially for those who would rather not ingest 10 or 15 servings per day.

  "We see a high level of demand for fortification in dairy products," Olson says. "Sour cream, ice cream, cheese, yogurt, milk and yogurt drinks." She mentions skim milk as a notable application. Adding 1% of the company's fractionated whey to skim milk boosts the calcium content by 10% to 20%, and increases whiteness and opacity. "We just received a Grade A status, which allows us to use it in Grade A products - fluid milk, sour cream, ice cream, yogurt, things like that. If you add dairy ingredients to a dairy product, they must be Grade A."

  Non-dairy items also make a good choice. Soy or rice milk or non-dairy coffee creamers lack the calcium of their dairy counterparts.

  "If you use a soluble form of calcium in a coffee whitener, it will produce white lumps," Kjelsberg says. "It's will flocculate to the top, and leave you with black coffee. If you use an insoluble form, it will sink to the bottom almost immediately." This is one area where using the protein/calcium carbonate complex makes a difference. The protein keeps the calcium in suspension longer, and the calcium provides a whitening effect. In addition, Kjelsberg has found that "the calcium cuts the bitterness of the coffee."

  Orange juice is another popular medium. It has two benefits when it comes to calcium fortification: its low pH, which increases solubility, and its somewhat opaque appearance, which gives less-than-completely-soluble versions a chance to be disguised. The levels used generally mimic those in milk: 30% to 35% of the RDI.

  Frozen juice concentrates can provide a benefit when it comes to calcium fortification, says King. "Because the product is frozen, and the reconstituted products are used almost immediately, there is not enough time for the calcium ions to react with citrate ions, etc., to form precipitates. This is in contrast to long shelf-life liquid products where precipitation may occur."

  In baked goods, calcium fortification can improve the nutritional profile. Calcium salts can be used, or a calcium/dairy-protein product utilized to provide additional benefits. Kjelsberg has noted better dough-handling characteristics with the use of New Zealand's High-Calcium proteins. "We found that the cookies didn't spread as far, and achieved a nice, even bake." When an insoluble calcium salt with the same particle size was used, the compound agglomerated and white particles appeared on the surface of the cookie.

  Some breakfast cereals have calcium fortification, but because they are typically consumed with milk, that practice isn't widespread. "There are technological reasons for it, too," van Mossevelde explains. "It's difficult to dissolve such a large volume of calcium required for a calcium claim in a dry product. It will have a large impact on the characteristics of the dough."

    Recently, a calcium-fortified rice product developed by Uncle Ben's, Houston, hit the market. Van Mossevelde believes sports drinks would be one area to tap to replenish calcium lost during exercise. But whatever the vehicle, calcium-fortified foods are here to stay. The National Institutes of Health reinforces this view in its report on calcium intake, "... the low energy intakes reported in recent national surveys may mean that it would be unusual to see changes in food habits to the extent necessary to maintain intakes by all individuals at levels recommended in this report. Eating fortified food products represents one method by which individuals can increase or maintain intakes without major changes in food habits."

Calcium Intake
(1997 Institute of Medicine Recommendations)



Adequate Intake (mg/day)

0 to 6 months

human milk content


6 to 12 months

human milk, plus solid food


1 through 3 yrs.

extrapolation of maximum calcium retention from 4 to 8 yrs.


4 through 8 yrs.

maximum calcium retention


9 through 13 yrs.

maximum calcium retention


14 through 18 yrs.

maximum calcium retention


19 through 30 yrs.

maximum calcium retention


31 through 50 yrs.

calcium balance


51 through 70 yrs.

maximum calcium retention


older than 70 yrs.

extrapolation of maximum calcium retention from 51 to 70 yrs.



18 yrs. or less bone mineral mass


19 through 50 yrs.

bone mineral mass



18 yrs. or less bone mineral mass


19 through 50 yrs.

bone mineral mass


All age groups (except pregnancy and lactation) include males and females.

  Adequate intake: The observed range or experimentally set intake by a defined population or subgroup that appears to sustain a defined nutritional state, such as growth rate, normal circulating nutrient values or other functional indicators of health.

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