Fast food may often be high in salt, but the exact levels seem to vary based on the country you live in, according to a study published Monday.

Looking at fast-food menu information in six countries, researchers found that the same item sometimes had different salt levels in different countries.

In general, certain foods had less salt in the UK than in the U.S. or Canada -- like McDonald's chicken nuggets and some chain-restaurant pizzas.

One serving of Chicken McNuggets, for example, came with 1.5 grams of salt (or 600 milligrams of sodium) in the U.S. and 1.7 grams of salt (680 mg of sodium) in Canada. That compared with just 0.6 grams of salt (240 mg of sodium) in the UK.

The chicken nuggets served up in Australia, France and New Zealand had salt levels that fell somewhere in between.

Salt was pervasive regardless of location, however. Overall, fast-food burgers served up an average of 1.3 grams of salt (or 520 grams of sodium) across all countries, with only small national differences.

According to the World Health Organization (WHO), people should get less than 2,000 mg of sodium over a whole day.

It's not clear why salt content in some fast-food items varied by country, said Dr. Norman Campbell of the University of Calgary in Canada, who worked on the study. He and a few of his co-authors are members of the World Action on Salt and Health, which according to its website "works to encourage multi-national food companies to reduce salt in their products and with Governments in different countries highlighting the need for a population wide salt reduction strategy."

One factor in the country differences could be UK government efforts, the researchers write in the Canadian Medical Association Journal. The UK has set voluntary salt-reduction "targets" for the packaged food industry.

The targets do not yet extend to fast food. But some fast-food companies were part of the "roundtable discussion" that helped set the goals, noted Elizabeth Dunford, a researcher at the George Institute for Global Health in Australia who led the study.

The bottom line, the researchers say in their report, is that salt reduction does appear feasible for fast food. The food industry has argued in the past that salt reduction is difficult because it requires new processes and technologies.

And a McDonald's spokesperson pointed out that the study used data from 2010.

"We have already reduced sodium by 10 percent in the majority of our national chicken menu offerings in the U.S. -- most recently Chicken McNuggets -- a Happy Meal favorite," the spokesperson said. "Sodium reductions will continue across the menu and by 2015, we will reduce sodium an average of 15 percent across our national menu of food choices."

SODIUM HIGH IN ALL FOODS

But Campbell said the study is not an attack on the fast-food industry.

Country-to-country variations are seen in packaged food, too. And heavy salt use is not unique to fast food, Campbell noted.

"Yes, salt in fast food is very high," he said. "But if you went to an expensive restaurant, the sodium levels would be very high. If you buy packaged foods, the levels would often be very high."

In the U.S., it's estimated that almost 80 percent of people's sodium intake comes not from their saltshakers, but from the salt that foodmakers add to their products.

Campbell argued that it's up to governments to rein in sodium levels in the food supply.

Companies, he said, answer to shareholders, and they are out to make the most profitable products. "The big issue here is not the companies. The big issue is the governments."

A "structured, voluntary approach" -- where the government works with industry to set lower salt targets -- is probably the most feasible, Campbell said.

That's the approach that's been taken in the UK. In the U.S., New York City has led the way, coordinating the National Salt Reduction Initiative.

The NSRI is a coalition of local and state governments and health groups working with industry to cut sodium in packaged foods and restaurants. More than two dozen food companies, including Heinz, Kraft Foods and Starbucks, have signed on to meet certain salt-reduction targets.

"The (NSRI) has set targets for restaurant foods and we hope that other countries will follow a similar path," Dunford said in an email.

Exactly what such efforts will do for public health is not clear yet.

Cutting down on salt is known to help lower blood pressure. And many experts believe that wide-scale cutbacks on salt in the food supply will lower rates of heart disease and stroke. The WHO lists salt reduction as one of its top 10 "best buys" for lowering rates of chronic disease.

IS LOWERING SALT ALWAYS GOOD?

Not everyone is convinced, though. A recent research review of 167 studies found that while salt reduction helped lower people's blood pressure, it may also boost levels of certain hormones and blood fats that could be harmful to the heart.

None of the studies had long-term information on whether salt reduction actually prevented, or contributed to, heart attacks or strokes.

The review was published by the Cochrane Collaboration, an independent, international organization that evaluates medical research.

But Campbell pointed to some other figures.

A 2010 study in the New England Journal of Medicine estimated that if Americans cut 3 grams of salt out of their daily diets -- or 1,200 mg of sodium -- it would save up to 92,000 lives each year. The typical U.S. man downs more than 10 grams of salt per day, while women average about 7 grams.

According to Dunford, the message for individuals is to eat fewer high-sodium foods -- not only fast food, but the many processed foods that harbor added salt, from breads and cereals, to processed meats, to soups and sauces.

But both Campbell and Dunford said that consumers should not bear all the responsibility.

"We've been badgering people about salt for years, and it's not working," Campbell said. "They are out there in a sea of fast food and processed foods."

"We really need to tackle this at a societal level."