October 22/Sydney, Australia/ABC Transcripts -- For years, consumers have been told a low salt diet is good for their health and especially the heart, but now a new study has challenged the effectiveness of that advice. While sodium consumption in the U.S. has not changed in more than 40 years, rates of high blood pressure are still on the rise.

Scientists analysed 38 studies in the U.S. between 1957 and 2003 that measured sodium levels in urine. They found no change in salt intake over a 46-year period.

"Although it showed no change it did still show that salt intake is well above the recommended maximum level of intake for the general population," states Elizabeth Dunford of The George Institute on Global Health.

Despite years of public health efforts to reduce salt consumption, this study suggests it has not happened, but health experts here say the advice is still warranted.

"They are justified," explains Susan Anderson of The Heart Foundation. "The science very clearly supports the fact that reducing salt intake will help lower blood pressure and therefore help to reduce heart disease."

There are no similar salt intake studies in Australia. Nutritionists say three quarters of our sodium consumption comes from processed food, and we eat much more salt than we need.

"Say, for example, if you reduced population salt intake by 3g," Dunford opines, "that would reduce the levels of cardiovascular disease by about a fifth, 20%."

U.S. researchers acknowledge their study has its limitations. They say it is possible sodium consumption has dropped since 2003 because of changes to processed foods. The first accurate estimate of salt intake by Australians should be known by the end of next year.

From the November 1, 2010, Prepared Foods E-dition