sealPurdue News
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May 1995

Purdue study shows calcium timing critical for young girls

WEST LAFAYETTE, Ind. -- A girl's first menstrual period is not only a rite of passage, it marks her best time to get the calcium she'll need to carry her body through the rest of her life, according to a Purdue University study reported in the March issue of The American Journal of Clinical Nutrition.

A landmark study by Purdue nutrition researchers found that the optimal period of calcium absorption in young women peaks near the onset of menses and declines for the remainder of their lives. Low calcium intake during adolescence has been associated with the eventual onset of osteoporosis, which causes weak, brittle bones in elderly women.

Professor Connie M. Weaver, head of Purdue's Department of Foods and Nutrition and principal investigator of the study, says: "One of the key findings of our study was that young girls retain more than four times as much calcium as women just a few years older." The research also suggests that young girls may be able to absorb higher levels of calcium than previously thought.

The 1990 study was conducted with 14 girls ages 11 to 14 and 11 women ages 19 to 32. For three weeks they were kept in a sorority house on the Purdue campus where calcium intake, diet and eliminations were closely monitored and measured. "Camp Calcium," as it was called, was intended to make up for some of the unknowns in calcium recommendations for young women.

Daily calcium retention for the adolescents was 326 milligrams per day compared to 73 milligrams per day for the women. Both groups were on diets that included exactly 1332 milligrams of calcium per day.

The study showed calcium absorption decreased with age, and the decline corresponds with postmenarcheal age, the number of years after a girl's first period. The Purdue study was the first to look at the relationship between menarcheal age and calcium retention, Weaver says.

The difference between the groups is largely due to better calcium absorption and reduced calcium excretion in the adolescents compared to the women. "Adults have leaky kidneys when it comes to calcium," Weaver says.

Because the Purdue researchers knew how much calcium each subject consumed, blood tests and waste analyses told the team how much calcium was absorbed by the skeleton. It was an exacting task, dealing in minute amounts where even the smallest differences can be critical.

"Eighty percent of bone density is genetically determined, and an individual can only manipulate about 20 percent," Weaver says. "But it's worth working on because a 5 percent increase in bone mass corresponds to about a 40 percent decrease in fracture risk."

According to the National Institutes of Health, osteoporosis affects 25 million people in the United States and is associated with 1.5 million fractures for a health care cost of $10 billion per year. Weaver participated in a NIH consensus conference on calcium last year that reported young women ages 12 to 19 years old consume well below the optimal recommended levels of calcium. Consequently, the NIH has singled out that group for special education measures.

It's too late for Dorothy E. Theller, though. The 74-year-old Tiffen, Ohio, resident was diagnosed with osteoporosis and back problems in 1981. She lives with pain, can't pick up her newborn grandson and moves cautiously.

A little more than a year ago, Theller broke her shoulder when she slipped and fell in her kitchen. It took six weeks in a sling and four months of physical therapy before the fracture healed enough for her to use the arm. It still hasn't come all the way back, and probably won't. Her greatest fear is someday fracturing her hip -- a common occurrence for people with osteoporosis -- and losing her mobility and independence.

Theller says she regrets not drinking milk or eating dairy products when she was a teen-ager and fashion told young girls they needed to be "thin and svelte."

"It would have made a great difference," she says. Today she warns her daughters and others about the consequences of poor nutrition and osteoporosis.

"Avoid it at all costs," Theller says. "It's foolishness to ignore the recommendations. When I was growing up we didn't know that."

Weaver, who specializes in nutritional minerals like calcium, says osteoporosis is completely preventable and her research tells young girls they can decide today the quality of life they want when they're older."Picture what you want to look like in 70 years. Do you want to be jogging or in a wheelchair?" Weaver asks.

Weaver held another Camp Calcium in 1993 and has requested funds for another camp next summer. She says she hopes to use the results to write specific "calcium prescriptions" for young women based on their physiological type and the time of their first menstrual period, so that they get the right amount of calcium they'll need for the rest of their life.

A Crossroads grant from the Indiana legislature provided Weaver with the seed money to start the project in 1990 and also allowed for training nutrition professionals. It has led to more than $1 million in funding from the National Institutes of Health to study the correlation between calcium intake and retention and to determine more specific calcium requirements for young women.

Sources: Connie Weaver, (765) 494-8237; Internet, weavercm@cfs.purdue.edu
Dorothy Theller, (419) 447-5943
Writer: Chris Sigurdson, (765) 494-8415; Internet, sig@ecn.purdue.edu
Purdue News Service: (765) 494-2096; e-mail, purduenews@purdue.edu

ABSTRACT

Differences in calcium metabolism between adolescent and adult females

Connie M. Weaver, Berdine R. Martin, Karen L. Plawecki, Munro Peacock, Olivia B. Wood, David L. Smith, and Meryl E. Wastney

A 3-week metabolic study measured calcium balance in 14 white adolescent girls and 11 young adult women. Subjects were housed in a sorority to simulate a free-living environment. A 6-day menu cycle consisted of foods typically eaten by teenagers and averaged 1,332 mg Calcium per day. Adolescents had a signifcantly higher calcium balance of 326 107 mg/d (x- SD) than adults, who averaged 73 104 mg/d (P<0.001). No adult >age 21 y was in positive calcium balance. Adolescents had lower urinary calcium excretion values (P<0.001), lower fecal calcium excretion (P<0.01), and greater net absorption (P<0.001) than adults. Calcium balance was negatively correlated with years postmenarche (r = -0.788, P = 0.0001) and height (r = -0.650, P = 0.001). Net calcium absorption was positively correlated with parathyroid hormone concentrations (r = 0.537, P = < 0.01). Thus the growth demands of adolescents are met by more efficent net absorption and retention of calcium compared with young adults. Am J Clin Nutr 1995;61;577-81

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