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Link Between Sodium and Osteoporosis
is Subject of New Study
September 20, 1999
t's an accident waiting to happen. From the time she enters menopause, a woman can be threatened with osteoporosis and not even know it - unless she suffers a fracture, commonly of the wrist, hip or even the spine, perhaps in a fall that didn't seem all that serious. Then the onslaught of this heretofore painless, silent disease becomes all too apparent.
"When estrogen is no longer available, the bones start losing mass very rapidly," says Jasminka Ilich-Ernst, associate professor of allied health and a registered dietitian. Less dense, they are also more fragile and tend to break easily.
Women who choose not to take hormone replacements or other drugs to prevent thinning, brittle bones, need natural interventions. The best known, calcium, is found mostly in dairy products, or it can be taken in pill form. How it is absorbed and used in the human body - especially its necessity for healthy bones - has been the focus of Ilich-Ernst's research for years.
"Eighty percent of bone density is genetically determined," she explains. "You inherit bones that are strong or weak, dense or fragile. But 20 percent we can manipulate, with food, life style, and other environmental factors. That's why preventing osteoporosis is so important."
Now concentrating on post-menopausal women in a major study, Ilich-Ernst, who came to UConn in 1998, wants to determine if those on a high-sodium diet will lose more bone mass in different parts of the body, as compared to women with a lower sodium intake.
She recently began a three-year longitudinal study, with 60 women followed per year, half on a low-sodium diet, half as control. The study is funded with a grant of $180,000 from The Patrick and Catherine Weldon Donaghue Medical Research Foundation.
"What we are sure of so far, in animals and in humans, is that the more sodium in the diet, the more calcium will be excreted in the urine," she says. The two minerals compete for reabsorption in the kidneys, and when there is more sodium present, less calcium gets reabsorbed.
Calcium, however, is relatively uncommon in foods, whereas sodium can be found in virtually everything we eat, including traces in fresh fruits and vegetables.
Given its importance for bone structure, Ilich-Ernst is concerned about where the increased urinary calcium is coming from. Her theory is that it is being drawn away from bones, where its loss will compromise them.
With half the participants in the study reducing their daily sodium intake to 1,500 mg (the average daily intake is more than 3,500 mg), she will do complete skeletal measurements of all participants at six and 12 months. "My hypothesis is that the postmenopausal women who keep their sodium intake low will lose less bone mass, or maybe even stay at the level of their baseline measurements," she says.
In her lab in Gampel Pavilion, Ilich-Ernst works with a dual X-ray absorptiometer that is capable of distinguishing between soft tissue and bone. As the subject lies on the gurney, an overhead detector arm tracks from head to toe, activating the X-ray housed in the bed. An analysis of fat, muscle mass and bone-mineral content adds to the composite of each individual and changes that may occur. The low radiation from the new equipment is about 30 times less than a regular chest X-ray, or about equal to the cosmic radiation a passenger receives on a flight from New York to San Francisco.
Interested in the total growth curve, Ilich-Ernst's work, first at the University of Utah and later at Ohio State, has shown how good nutrition and abundant calcium, coupled with more effective, weight-bearing exercise will achieve higher peak bone mass, with continued benefits throughout adult life.
Her two daughters, now 18 and 21, have been lifelong participants in her studies. The younger just finished a seven-year study begun at Ohio State. "Her bones are the most examined bones ever," her mother says.
Ever the scientist, when Ilich-Ernst broke her own arm last winter, she even put herself "under the microscope" to better understand the healing process of bone.
The ultimate objective is to eliminate the threat of osteoporosis, now more prevalent as people live longer. Women are at greatest risk, four times more susceptible than men, for whom it is generally only an issue in the very elderly. The disease affects more than 25 million Americans, and is estimated to cost the U.S. economy some $13.8 billion a year.
Usually problems don't show up until the later years, after menopause. But the person whose early bone growth was hindered by poor nutrition and lack of exercise may "end up in the fracture threshold much earlier than another, who might never come to that point," says Ilich-Ernst.
"Even 10 years ago, if you'd asked me whether anything could be changed, I would have said, 'No, it's probably too late.' But now we know better," she says, adding that research in the area has expanded our knowledge and has given us some very powerful drugs. We also know now that taking calcium supplements and exercising at age 60 can still make a difference. "Bone is a live tissue, in a constant process of formation and degradation. It's just like skin in that way," she says.
"While you may not be able to do much to boost your bone mass or bone-mineral content without taking powerful drugs, at least you can slow down the bone loss," Ilich-Ernst says. "That's the whole key, to slow the process, so you won't reach the fracture threshold."