The sodium content of more than 28,000 processed foods has risen an average 9 per cent in the past four years, researchers have found, warning urgent action is needed to reduce people's salt intake.

A senior director of Sydney University's George Institute for Global Health, Bruce Neal, said excess sodium caused high blood pressure and was a main factor in heart attack and stroke. He said processed foods were the main source of salt, and the 9 per cent rise was contrary to federal government and food industry programs to reduce it.

Researchers from the institute recorded the sodium content of most packaged food products in five supermarkets between 2008 and last year.

Overall the mean sodium content rose 9 per cent, but varied across product categories. Sodium content was up 16 per cent in oils, 13 per cent in sauces and spreads and 8 per cent in cereals.

Foods in which the average sodium content was reduced included dairy foods ( down 11 per cent) and bread and bakery products (down 8 per cent).

Professor Neal said a 9 per cent rise in sodium intake across the population would lead to a 4 per cent increased risk of stroke and heart attack.

''That would translate into 2000 more deaths each year as a consequence of these foods having got saltier,'' he said.

Professor Neal said the rise was particularly high in new products that came onto the market during the study. He said the results showed programs to reduce salt in food - including the federal government's food and health dialogue in which manufacturers commit to voluntary targets - were making little headway.

''Few products have had targets set, there is no requirement for companies to participate, the timelines for delivering product improvement are very long and there is no objective third-party reporting of progress,'' he said.

Professor Neal said the program should be urgently upgraded to set targets, regularly report progress and plan for regulation if voluntary efforts were ineffective.

Federal parliamentary secretary for health Catherine King said earlier this year that the program had achieved a 1000-tonne reduction in salt in the bread sector, and work was under way to reduce salt in savoury pies.