Maximizing Calcium Absorption

To fight the growing incidence of osteoporosis, calcium-fortified foods and beverages are essential. Yet calcium is complex, and many factors influence this vital nutrient’s absorption, including the type of calcium consumed, whether calcium is consumed in a fed state or on an empty stomach, the food it is consumed with, and the total calcium consumed at one time.

Importance of calcium

Calcium helps bones grow in length during adolescence, and in density up until approximately age 30, when peak bone-mineral density is achieved. After this age, bone-mineral density declines, but maintaining adequate calcium and vitamin D levels and participating in weight-bearing exercise can attenuate this decline. Maintaining bone-mineral density is crucial to preventing osteoporosis and helping bones withstand the force of impact without breaking.

Calcium plays other important roles in the body. It helps regulate muscular contractions and plays a role in normal nerve functioning, blood-vessel expansion and contraction, and hormone and enzyme secretion. When dietary calcium intake falls short, calcium is pulled from its storage site in bone to meet the demands of the body and keep calcium in blood, muscle and intercellular fluids within a constant concentration.

Calcium absorption

Several factors affect how much calcium is absorbed in the gut. These include age, the amount of calcium consumed in one sitting, vitamin D intake, other food components and the type of calcium consumed.

Infants and young children absorb significantly more calcium than adults, up to 60% of their calcium intake, because they need more to support bone growth. Calcium absorption decreases in adulthood and continues to decrease with age. Adults absorb just 15% to 20% of intake, according to the Food and Nutrition Board, Institute of Medicine.

Calcium absorption decreases as the calcium content of a meal increases. Therefore, it is generally recommended that people consume 500 mg or less calcium per serving. Serum vitamin D status also affects calcium absorption. Low serum vitamin D levels decrease intestinal calcium absorption (Journal of Human Nutrition and Dietetics, 2010; 23(1):54-60), and several studies indicate many people have insufficient or deficient levels of vitamin D (“What We Eat in America,” NHANES 2005-2006; Journal of Nutrition, 2007; 137:447-452; European Journal of Clinical Nutrition, 2009; 63:1,377-1,386). Phytic acid, found mainly in whole-grain products, beans, seeds, nuts, soybeans and soy protein, binds to calcium, inhibiting its absorption. Likewise, oxalic acid, which is mainly found in dark-green leafy vegetables, sweet potatoes and beans, also binds calcium, inhibiting its absorption. Though some types of dietary fiber also decrease calcium absorption, the prebiotic fiber inulin enhances calcium absorption (Journal of Nutrition, 2007; 137:2,527S-2,533S).

Formulating with calcium

Given the number of Americans consuming less than the Adequate Intake for calcium, calcium-fortified foods and beverages may help fill the gap, giving consumers more options for meeting their calcium needs. Fortification should be considered carefully and in conjunction with other bone-building nutrients, such as magnesium and vitamins D and K2.

“The challenge for formulators is to select an appropriate form of calcium that delivers the desired level of the mineral without affecting flavor, solubility, bioavailability, sensory properties and the mouthfeel of the finished product,” says Ram Chaudhari, Ph.D., senior executive vice president and chief scientific officer, Fortitech, Inc., Schenectady, NY. “Some of these processing issues can be prevented if a blend of calcium sources is used instead of a single source.”

Further, notes Nadeen Myers, food phosphates specialist, ICL Performance Products LP, St. Louis: “The challenge with calcium fortification is that the solubility of calcium phosphates is pH-sensitive, so that clarity of solutions may be an issue. However, there are many types of food and beverage products that still successfully use calcium phosphates for fortification. This includes solids like nutrition bars, yogurts or puddings, and opaque beverages like fruit-based drinks or juices.”

Chaudhari suggests food manufacturers work closely with their suppliers to address product-development issues that could impact calcium delivery or alter the end product. “The supplier can suggest appropriate market forms of calcium, interactions to avoid and processing effects that will improve the chance of success,” he notes.

Chaudhari recommends answering the following questions prior to fortifying a product with calcium:

• What type of product will be fortified?

• How much calcium needs to be added (especially if a manufacturer is trying to meet label claims)?

• Will additional ingredients, such as vitamin D or other nutrients, be added to enhance calcium absorption?

• What are the processing conditions, such as time and temperature?

• What is the pH of the finished product?

• What are the shelf life and other components of the finished product?

Calcium ingredients

A variety of types of calcium can be used to fortify foods and beverages. The decision to choose one type over another is dependent on how well it works in the particular food or beverage application based on solubility, taste and palatability. Bioavailability is important, but it comes second to taste, because consumers will not continue buying a product with an off taste or texture.

According to a study published by the USDA’s Agricultural Research Service, (Journal of the American College of Nutrition, 2009; 28:73S-81S) “recommending 3 to 4 servings from the dairy group for all people greater than 9 years of age may be necessary in order to ensure adequate intake of calcium and magnesium, assuming the current diet remains the same."

Dairy foods play an important role in meeting people’s calcium needs. “Milk and milk products provide nearly 75% of the calcium available in the U.S. food supply,” says Erin Coffield, R.D., L.D.N., and spokesperson for the National Dairy Council, Rosemont, IL. “In addition, we know that vitamin D increases calcium absorption. And, milk is the No. 1 source of vitamin D in the American diet, and now many yogurts and some cheeses also are fortified with vitamin D.” For these reasons, using dairy products as a base, or adding dairy, will boost the bone-building compounds within the food or beverage.

Each calcium mineral salt has its benefits and drawbacks. Common calcium mineral salts for food and beverage fortification include calcium carbonate, calcium phosphate, tricalcium phosphate, calcium citrate, calcium lactate, calcium lactate gluconate and calcium gluconate.

Calcium carbonate may be better suited for supplements than fortified foods since it can taste chalky or soapy. However, one advantage of adding calcium carbonate is that it is best absorbed when part of a food.

“Calcium phosphate salts are excellent sources of calcium and can be used to maximize the calcium available in foods and beverages,” says Myers. “In order to maximize the level of calcium obtained in a formulation, tricalcium phosphate may be a good choice since it contains a very high percentage of calcium by weight: 40% calcium.” In addition, tricalcium phosphate has the added benefit of phosphorus, which is necessary to promote the absorption of the calcium in bones, she notes. Certain populations may have a low phosphorus intake, notably women between the ages of 60 to 80 (Journal of the American College of Nutrition, 2002; 21:239-244). Tricalcium phosphate is often used as an anti-caking agent and food additive, though it can also be used to boost the calcium content of a product. Calcium phosphate is flavorless.

Calcium citrate is typically bitter, but some forms are virtually flavorless. It is relatively soluble at a low pH, and absorption doesn’t depend on food intake. Calcium lactate and calcium gluconate are both flavorless and highly soluble.