May 27, 2002 Eating potassium-rich foods such as bananas, tomatoes and orange juice can help prevent osteoporosis for postmenopausal women by decreasing calcium losses, according to a UCSF study.
In postmenopausal women the consumption of excessive salt has been shown to increase the level of bone minerals excreted through urine, although salt does not seem to effect younger women or men in a similar fashion, said study author Deborah Sellmeyer, MD, UCSF assistant adjunct professor of endocrinology and metabolism. While the benefits of dietary calcium and vitamin D for preserving bone density have long been established, the UCSF study is the first to examine the role of potassium in preventing bone density loss exacerbated by a high-salt diet.
Osteoporosis affects an estimated 44 million Americans, mostly women. It causes bones to become fragile and more likely to fracture. The National Osteoporosis Foundation estimates that 55 percent of Americans aged 50 and older are at risk for the largely preventable disease. "For women at risk of osteoporosis, eating more fruits and vegetables is a simple way to help prevent the adverse effects of a typical American high salt diet," said Sellmeyer.
Although no studies have directly measured the level of dietary salt necessary to adversely affect bone mineral excretion, Americans eat twice as much salt (sodium chloride) as they should, according to the National Institutes of Health (NIH). The NIH recommends consumption of no more than 6 grams, or about 1 1/2 teaspoons, of salt daily for cardiac health.
In the UCSF study, 60 healthy postmenopausal women were placed on a low salt diet (two grams / day) for an initial three weeks while their level of excreted calcium was measured. The level of excreted NTX, a bone protein, was also measured. A higher NTX level indicates that more bone is being broken down, or reabsorbed, leaving women at increased risk for fractures.
At the end of three weeks, all the participants were placed on a high salt (9 grams/ day) diet. Half were given a potassium supplement and half were given a placebo. For four more weeks they continued the high salt diet. At the study’s end, researchers were able to compare each woman’s low and high salt diet results individually. They were also able to compare the loss of calcium and NTX between the placebo group and the group receiving potassium. Calcium loss increased 33 percent for women taking the placebo, but decreased four percent in the potassium citrate group.
For women taking the placebo, NTX excretion increased 23 percent, but in women taking potassium citrate, it increased only 7.5 percent, suggesting that their bones were remaining healthier than the bones of women receiving only placebo. "When they went from a low salt diet to a high salt diet plus potassium, there was no change," said Sellmeyer. But increased dietary salt increased urinary calcium excretion in the women who received only placebo, and their enhanced calcium excretion was associated also with increases in NTX, suggesting skeletal effects, the authors said.
The potassium dosage used in the test was 3.5 grams daily, or about the amount in 10 bananas. Other potassium-rich foods include spinach, melon, and potatoes. Since most dietary salt comes from processed food, the authors said the total sodium and chloride content of one’s diet is important to consider.
The study was funded by the National Institutes of Health and published in the May issue of the Journal of Clinical Endocrinology and Metabolism. Additional authors are Monique Schloetter, MS, RD, research dietitian in the UCSF General Clinical Research Center and Anthony Sebastian, MD, UCSF professor of medicine.
May is National Osteoporosis Prevention Month.
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