Roanoke Times
Copyright (c) 1995, Landmark Communications, Inc.
DATE: TUESDAY, August 31, 1993 TAG: 9308310020
SECTION: EXTRA PAGE: 1 EDITION: METRO
SOURCE: JANE BRODY
DATELINE: LENGTH: Medium
But mounting evidence indicates that this late-in-life concern about bones is like shutting the barn door after the horse has escaped.
For it turns out that many, if not most, women enter adulthood with their bones already on the losing side because they failed to consume enough calcium during adolescence, when bone development reaches its biological peak.
And if calcium intake by today's youth is any indication, the current "epidemic" of osteoporosis is likely to reach gargantuan proportions in the decades to come, when the girls who grew up on diet soda pass through menopause.
Osteoporosis, which is much more of a problem for women than for men, is not the only consequence of a chronic calcium shortage. There is mounting evidence that high blood pressure (which is particularly common among black Americans, whose calcium intake is considerably below that for whites) and colon cancer are also linked to inadequate calcium in the diet.
In the most recent national nutrition survey, conducted from 1976 to 1980 among 4,342 children 3 to 18 years old, teen-age girls, both white and black, consumed significantly less than the recommended daily intake of calcium: 1,200 milligrams a day.
According to the survey findings, analyzed by Linda H. Eck, a nutritionist at Memphis State University, and Dr. Catherine Hackett-Renner, of Christian Brothers University in Memphis, teen-age white girls averaged only 799 milligrams and black teen-age girls consumed only 626 milligrams of calcium daily.
For black boys, the average level was only slightly better, 896 milligrams. The daily requirement was met only by teen-age white boys, with an average intake of 1,339 milligrams.
Although more than a decade has elapsed since the survey was completed, experts say there is no reason to think that teen-agers' calcium intake has improved. If anything, current teen-age dietary habits suggest that the situation has worsened.
Aside from the milk that might be consumed in breakfast cereal by the few teen-agers who eat a nutritious breakfast, milk, a main source of dietary calcium for Americans, plays little or no role in the diets of adolescents. This leaves the cheese on pizza and the milk in ice cream as perhaps the most reliable calcium sources for American teen-agers.
Yet it is during the teen-age years that a high calcium intake is most important for building a healthy skeleton. As one expert, Dr. Tom Lloyd, of the Pennsylvania State University's College of Medicine in Hershey, explained, the teen-age years are particularly critical because the hormones released during puberty increase the rate at which bones are built.
After the age of 20, when bone mass reaches its natural peak, the bones of many, and perhaps most, women gradually decline in density until menopause, when bone loss accelerates rapidly unless it is countered by measures like hormone replacement and regular weight-bearing exercise.
Factors other than simple calcium deficiency can worsen bone decline in young women. A two-year study of 30 white women aged 13 to 29 showed that bone density was jeopardized if heavy exercise disrupted menstrual cycles.
Even when those women's menstrual periods resumed, their bone development lagged, and the researchers say bone growth may remain chronically behind, placing the women at higher-than-average risk of developing osteoporosis in their later years. The study was published last May in the journal Obstetrics and Gynecology.
Women who nurse their infants for more than six months also lose a significant amount of calcium from their bones, according to a report last June in The Journal of the American Medical Association.
In a study of 98 women, conducted by researchers at the University of Michigan in Ann Arbor, all the participants were healthy and consumed large amounts of calcium, at least the 1,250 milligrams a day recommended for nursing women.
Still, those who nursed their infants for six months or longer experienced about a 5 percent loss of bone density in their lower spine and upper thigh bones.
Among those who weaned their infants between six and nine months, the average bone density returned to normal by the time their babies were a year old.
Those who nursed beyond nine months were still recovering their bone density when their babies were a year old, and it was not known how complete that recovery would be.
"The jury is still out on whether recovery will be complete for those who breast-feed longer than nine months," said the researcher, MaryFran Sowers. "We also don't know the impact of subsequent births." New York Times
\ Jane Brody writes about health issues for The New York Times.
by CNB