Potassium-rich foods such as bananas, tomatoes and orange juice could help fight osteoporosis in post-menopausal women by helping to reduce the level of calcium losses, report researchers from the University of California San Francisco (UCSF).
The researchers, led by Deborah Sellmeyer, UCSF assistant adjunct professor of endocrinology and metabolism, based their studies on earlier findings that showed that the consumption of excessive amounts of salt by post-menopausal women can lead to the excretion of high levels of bone minerals through the urine. Salt does not appear to affect young women or men in the same way, however.
Sellmeyer said that while there was also substantial evidence to show that dietary calcium and vitamin D can help preserve bone density, the UCSF study was the first to examine the role of potassium in preventing bone density loss exacerbated by a high-salt diet.
She added that no studies had directly measured the level of dietary salt necessary to adversely affect bone mineral excretion, but stressed that most people consumed far more salt than was good for them.
In the UCSF study, 60 healthy post-menopausal women were placed on a low salt diet (two grams per 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 per cent for women taking the placebo, but decreased four per cent in the potassium citrate group.
For women taking the placebo, NTX excretion increased 23 per cent, but in women taking potassium citrate, it increased only 7.5 per cent, 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 led to higher levels of 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.