The scientific community, including the National Research Council (NRC) and U.S. Surgeon Gen. C. Everett Koop, has a bone to pick with women who regularly fail to meet the Recommended Dietary Allowance of 800 milligrams of calcium or who do so by swallowing calcium tablets in lieu of low-fat foods. There is concern that the importance of continuously replenishing the body's supply of the mineral through dietary sources has been under-evaluated and overshadowed by the fear of fat in the diet.
A report released earlier this month by the NRC stressed the need for young and adolescent women to increase their intake of dietary calcium. The Surgeon General's Report on Nutrition and Health, published last year, also addressed this topic.
"Calcium is an essential nutrient," the NRC report stated. "It is necessary for adequate growth and skeletal development. Certain segments of the population, especially women and adolescents, need to make careful food choices to obtain adequate calcium from the food supply. The committee recommends that consumption of low- and nonfat dairy products and dark green vegetables, which are rich sources of calcium, can assist in maintaining calcium intake at approximately the RDA levels."
Furthermore, the report continues, "the potential benefits of calcium intake above the RDAs to prevent osteoporosis or hypertension are not well-documented and do not justify the use of calcium supplements."
Figures taken from the USDA's nationwide food consumption survey found that in 1985 women between the ages of 19 and 34 managed to achieve only about 80% of the RDA of calcium from food sources. Calcium intake for women in the 35- to 50-year-old age range, dropped to as low as 68% of the RDA--which is itself under scrutiny for being too low.
And since 1984, when a National Institutes of Health panel concluded that post-menopausal women needed twice the RDA of calcium and pre-menopausal women needed 1 1/2 times the RDA, supplement sales have "skyrocketed," USDA reports.
To improve consumer intake of dietary calcium, researchers have launched a triple attack. They are re-emphasizing the importance of building bone during the formative years, noting that older women consuming less than half the calcium needed over a prolonged period can suffer a loss of nearly 5% of spinal bone per year. They are stressing that the female hormone estrogen has a significant role in bone loss. And they are citing the negative effects of meeting the recommended goal through supplementation.
Research data indicates that taking extra calcium after menopause probably doesn't slow bone loss and building additional bone during youth--when the soft tissue inside the bones is in a continuous state of development--is the best insurance against osteoporosis later in life.
This was underscored most recently when studies of high calcium intake in older rats were completed. The research was directed by Dr. James C. Smith, head of the Vitamin and Mineral Nutrition Laboratory at Beltsville, Md., part of the government's Agricultural Research Service.
"I think there's a body of evidence that the best way is to build up the bones before menopause," Smith said in an interview, adding, "but I haven't worked with women."
His investigation was conducted at the Beltsville lab by University of Maryland graduate students under the direction of Joseph H. Soares, nutrition professor.
It is scientific fact that the body's ability to absorb calcium is variable with age. During typical periods of growth, intestinal absorption of calcium increases, with infants and children absorbing up to 60% of the calcium they ingest. Pregnant women use about 50% and other adults only retain about 30%. Calcium available from supplements is often even less, depending upon the binders used in the product, which can hold onto the calcium and prevent the body from using it. The ability of an individual's stomach acid to dissolve the supplements also is associated with malabsorption.
And there are other factors: bone loss accelerates naturally after age 35 and becomes more and more difficult to retard with age; after menopause a steady decline of estrogen--an important component in bone mineralization--is observed, and the process of bone development appears to slow down as an animal ages, making the bones solid, more brittle and thus less efficient at storing calcium.
(Ninety-nine percent of the body's calcium is stored in the bones and teeth. But it is used for various bodily functions. These include: regulating cell and nerve functions, maintaining normal blood pressure, muscle contraction capabilities including maintaining heartbeat, clotting of blood and preserving the material that holds cells together.)