Building Better Bones

October 2000

Osteoporosis is a condition characterized by substantial bone loss affecting the entire skeleton (most commonly the hips, wrists and spinal vertebrae), and affects more than 28 million American men and women annually.

Bones are in a continuous state of dissolution and reformation. Osteoporosis occurs when bone formation and bone resorption are out of balance; usually the former can’t keep up with the latter. This condition is influenced by two main factors: peak bone mass attained and the rate at which bone is lost in later years.

Peak bone density is reached between the ages of 30 and 35. Thereafter, the process reverses and bones begin to lose density. Post-menopausal women can lose 2% to 3% of their bone mass per year. In fact, if accelerated loss is not halted, a susceptible woman can lose 50% of her peak bone mass by the age of 70 or 80. Men between 65 and 70 years of age have an increased risk of fractures, primarily because of declining hormones, a more sedentary lifestyle and a change in the ability to absorb and use calcium.

Calcium concerns

Calcium is the major bone mineral. Adults between the ages of 18 and 50 require 1000 mg of calcium per day, while those over 50 need to consume 1200 mg per day. New recommendations were released in 1997, stating that children 10 and older should consume 1,300 mg of calcium daily — an increase of 500 mg from the previously recommended level of 800 mg. A total intake of up to 2,000 mg calcium per day appears to be safe for most people.

According to the "Third National Health and Nutrition Examination Survey (NHANES III) 1988-91," the following population groups do not generally consume the Recommended Dietary Allowance (RDA) of calcium: all adolescents except non-Hispanic white males, all females ages 12 and older, non-Hispanic black males 12 years and older and all males 60 years and older.

Absorbing facts

"Calcium is absorbed by an active and passive process, whereby the active process requires no other nutrient and the passive process requires vitamin D," says Connie Weaver, Ph.D., distinguished professor and department head, department of foods and nutrition, Purdue University, West Lafayette, IN.

"The amount of calcium absorbed depends on the physiological status of the host and the load (or amount consumed). The average for a premenopausal woman on a load of 300 mg (the amount in a glass of milk) is about 30%, or 90 mg," explains Weaver.

The body can absorb a higher percent of the calcium consumed during the growth stage than it can later in life. In fact, children and adolescents can absorb up to 75% of dietary calcium. The absorptive ability of the intestine diminishes with age; which may be one of the causes of bone loss.

If dietary calcium levels are low, the intestine compensates by absorbing more calcium. On the other hand, if we consume more calcium than what is needed, we will absorb less. "Unabsorbed calcium is excreted in the feces and excess absorbed calcium is excreted in the urine. There is an obligatory loss of calcium in both feces and urine regardless of the calcium intake. Hence, individuals can be in negative calcium balance," explains Weaver.

Diet can also affect the amount of calcium absorbed. Excessive levels of sodium and protein can significantly increase urinary calcium excretion, according to the National Institutes of Health. High levels of oxalate and phytate that occur naturally in certain foods, such as spinach, can reduce calcium availability in those foods but not in other calcium-containing foods ingested at the same time. Most fiber, with the possible exception of high levels of wheat bran, will not negatively affect calcium absorption. Other dietary components, including fat, phosphate, magnesium and caffeine, have not been found to affect calcium absorption or excretion significantly.

Balanced bones

"Since bone is a living tissue, all essential nutrients are needed, especially calcium, magnesium, phosphorus, vitamin D, vitamin K, protein, copper, iron, zinc and boron," says Weaver. There is a 2:1 ratio of calcium:phosphorus found in the bone, with about 80% to 85% of phosphorus located in the skeleton.

"It is important to maintain the proper balance of all essential minerals that comprise the bones," says Stacey Goebel, technical sales manager, Glanbia Ingredients, Monroe, WI. "An improper ratio of these minerals can lead to bone brittleness and calcium depletion."

Edward Bastian, Ph.D., director research and development at Glanbia says, "A high dietary calcium and low dietary magnesium can reduce the absorption of calcium, causing vitamin D to form hormonally inactive metabolites and impair the release of parathyroid hormone. To maintain proper composition of mineral in the bone, there must be adequate absorption and delivery of all bone minerals to bone sites in the human body."

Boning up on calcium

According to the "Optimal Calcium Intake NIH Consensus Statement" published in 1994, "The preferred approach to attaining optimal calcium intake is through dietary sources. Additional strategies include the consumption of calcium-fortified foods and calcium supplements. For many Americans, dairy products are the major contributors of dietary calcium because of their high calcium content (e.g., approximately 250 to 300 mg/8-oz. milk) and frequency of consumption."

Because many forgo milk-drinking these days, calcium-fortified foods are gaining in popularity. For those looking to formulate fortified foods, specialized premix formulas addressing bone health are becoming more available. "A premix should contain key nutritional ingredients for bone health, including calcium, phosphorus, magnesium, vitamin D and soy isoflavonoids, which some studies have shown to help with osteoporosis," says Lucia Ponginebbi, Ph.D., senior product development manager, Watson Nutritional Ingredients Division, West Haven, CT.

Other ingredients may assist in the body’s calcium absorption. "With the most recent study, only 8 grams of an enriched inulin have been shown to boost calcium absorption by 18% to 20%," says Kathy Niness, ORAFTI Active Food Ingredients, Malvern, PA. "Currently, we have not fully elucidated the mechanism, but one theory is that the colon acts as a second site of calcium absorption - usually it’s just absorbed in the small intestine." Products like these can help us all build better bones.

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