The research, published in the journal Progress in Cardiovascular Diseases (Vol. 49, pp. 59-75), could increase pressure on the food industry to reduce salt content in a wide range of foods.
"The increased intake in salt [since] has apparently played an important role in the increase in the consumption of soft drinks and, hence, also in the increase in energy intake," wrote authors Dr. Heikki Karppanen of the University of Helsinki and Dr. Eero Mervaala of the University of Kuopio.
"Higher consumption of sweetened beverages was associated with both a greater magnitude of weight gain and an increase risk for development of type-2 diabetes," they wrote.
Obesity is currently thought to affect more than 64 percent of the US's adult population and 16 percent of children, and has been repeatedly linked with an increased risk of other health conditions such as heart disease and diabetes.
Looking at their home country, Karppanen and Mervaala report that an average 30 to 35 percent reduction in salt intake during 30 years in Finland was associated with a 75 to 80 percent decrease in both stroke and coronary heart disease mortality in the population under 65 years.
They also report that life expectancy of both male and female Finns increased by 6 to 7 years during the same period.
And the reason behind these statistics is most likely the 10 mmHg and more decrease in the average blood pressure of the population, said the researchers. Numerous scientists are convinced that high salt intake is responsible for increasing blood pressure (hypertension).
In the US, meanwhile, the scientists report that average salt intake per person since the mid-1980s has increased, from an average of 10.2 grams per day per person to "more than 15 grams per person a day."
This is equivalent, they said, to a 55 per cent increase in per person salt intake.
Age-adjusted blood pressure has also increased since the late 1980s, said the researchers. This increase, wrote Karppanen and Mervaala, "appears to coincide with the turn of the sales of food-grade salt from a decreasing trned to a rapid increase in the later 1980s and in the 1990s."
The study reports that increasing intakes of sodium (salt) obligatorily produce a progressive increase in thirst, and between 1977 and 2001, the energy intake from soft drinks also increased by 135 percent, adding about 278 kcal to the average person's daily energy intake.
During the same time scale, the incidence of obesity has also rocketed, report the researchers, with an average rise of 57 per cent during 1988-1994, and then to 110 per cent during 1999 to 2002, compared with 1976 to 1980 figures.
"In the United States… the practical question therefore is how to decrease the overall additions of salt to the foods of the nation from the current levels of 1500 million kg per year to 1000 mg or, preferentially, to 750 million kg per year," wrote Karppanen and Mervaala.
In the USA, like in the UK and Ireland, over 80 percent of salt intake comes from processed food, with 20 percent of salt intake coming from meat and meat products, and about 35 percent from cereal and cereal products.
"The repeated warnings of various industries on possible harmful effects of comprehensive salt reduction are unjustified and even unethical," said Professor Karppanen in a statement.
Richard Hanneman, president of the Salt Institute, an association for salt producers, was quick to respond to the research and wrote in the SaltSensibility blog: "This claim that low-salt diets "would be a powerful means against obesity" is just over the top."
In a letter to Professor Karppanen and reproduced in the blog, Hanneman states: "While salt intakes in the U.S. have increased in the past 15 years, they track population increases. The U.S. population is 300 million today. We've added 50 million in population in those years.
"Of course, correlation is not causation, but to correlate salt intake with the rise in obesity ignores evidence that those on higher salt diets are actually leaner than other Americans. Just as obviously, the longest-lived national population in the world, the Japanese, have much higher salt intakes than Americans," he said.
However, Professor Karppanen told FoodNavigator that he has not received any kind of correspondence (letter or e-mail) but has since become aware of Mr. Hanneman's comments and responded to him. Professor Karppanen said that Mr. Hanneman has not replied.
Prof. Karppanen also responded to Mr. Hanneman's statements above and told this website: "[Mr. Hanneman] must also know that his claims that those with higher salt intakes are leaner than other Americans, are based on severely flawed data.
"Moreover, Hanneman's reference to Japan as a high-salt country with less diseases is not valid. Japanese studies have clearly indicated that decreasing salt intake would 1) lower stroke mortality in Japan and 2) decrease stomach cancer mortality in Japan. There are numerous other studies with the same conclusions," said Professor Karppanen.