Has the push to reduce salt intake gone too far

IF you've heard the warnings of the perils of eating too much salt _ but can't wean yourself off the fish and chips, and still like an extra sprinkle on top _ you're not alone. After decades of hearing of the harmful effects of high-sodium diets, most Australians have ignored the advice.
But a study published recently in the American Journal of Medicine has suggested maybe that's not such a bad thing after all.
Researchers at the Albert Einstein College of Medicine in New York found that people on low-sodium diets were 37 per cent more likely to die of cardiovascular disease and 28 per cent more likely to die of strokes than those with higher-salt diets (AJM 2006;119:275.e7-275e.14).
The study analysed data from more than 7,000 people who had been asked to recall everything they'd eaten or drunk over 24 hours as part of the National Health and Nutrition Examination Survey between 1976 and 1982. In 1992 the NHNES II tracked mortality in the same population.
Researchers included only the results of healthy people who had no medical reason to be on a special diet, and controlled for other cardiovascular risk factors such as blood pressure, cholesterol, sex, age, and other medication use.
Their hypothesis was that although dietary salt was cut, this prompted the body to increase levels of a hormone called plasma renin, which is nature's way of keeping blood pressure up _ a possible mechanism that could explain the increased cardiovascular risk.
In some studies plasma renin has been shown to be an independent predictor of cardiovascular events.
A study published by researchers from Albert Einstein College in 1995 in the journal Hypertension had similar findings: hypertensive patients on low-salt diets were thinner, excreted less potassium, and had higher plasma renin _ and they were four times more likely to die of heart disease than those who consumed more sodium (1995;25:1144-1152).
So does this mean you can now guiltlessly indulge in as much salty seasoning as you desire? And in fact do it in the name of good health?
Hillel Cohen, lead author of the AJM study, acknowledges that more research needs to be done, but says as yet there's not enough evidence to tell the general population they should change their habits.
``This was an observational study and not a clinical trial, so we can't really conclude from our findings that low-sodium intakes are harmful,'' he says.
``But our study certainly doesn't support the idea of a universal prescription for lower salt intake.''
But other health experts and researchers adamantly disagree.
Many have questioned the adequacy of the data Cohen and his colleagues used.
``The problem is this study didn't actually measure salt intake directly,'' says Caryl Nowson, an associate professor of nutrition and dietetics at Deakin University.
To get a reliable idea of what people's sodium intake actually is, she says researchers need to measure multiple times, not merely on one 24-hour occasion when any number of factors, from a party to a meal at a friend's house, could have altered the results. Dietary recall, where researchers use a food database to estimate the amount of salt a person consumes based on what they say they ate, is also far less accurate than urinary samples, she says.
``The food database is too limited. If you take five types of bread you'll get five different amounts of sodium. It also works under the assumption that the salt intake of a person on one particular day accurately reflects their sodium intake over a sustained period,'' Nowson says.
But the bottom line, according to Bruce Neal, director of the Cardiac and Renal Division of The George Institute in Sydney, is the case against salt is too solid to dismiss without substantially stronger research.
``Out of the observational studies that have been done, some say more salt, more risk. Some say more salt, no risk. Some say more salt, less risk _ so you haven't got a consistent answer,'' Neal says.
According to the guidelines set up by the National Health and Medical Research Council, a healthy diet should include no more than six grams of salt a day _ just over one teaspoon _ but preferably less.
``That was based on feasibility, not what was strictly the best,'' says Dr Trevor Beard, honorary research fellow at the Menzies Research Institute, which is one of the World Health Organisation's collaborating centres for population-based cardiovascular disease prevention programs.
``It was what they thought people could manage. Your body really only needs about one gram of sodium.''
But actual intakes are far higher than this 6g limit, - with the average Australian consuming over 9g every day, Nowson says. Figures from the UK show 20 per cent of men eat triple the recommended amount, a number Nowson says is likely to be similar here.
Slashing salt intake is especially difficult given that most of the salt you consume is well disguised in processed foods, rather than added with a shaker at the table, which accounts for just 10 to 15 per cent of your daily intake.
Everything from tinned tomatoes to sweet biscuits contain sodium _ and often more than you think. To be classified as ``low sodium'' a food must have less than 120 milligrams of sodium per 100 grams of the foodstuff.
In the UK, the government launched a 4 million pound advertising campaign in 2004 urging people to cut down on salt, and has even legislated a requirement for companies to lower the amount of sodium in the food they are selling by 2010.
The reason for the anti-salt push is simple: sodium increases blood pressure, and that's a fact no one on either side of the debate is disputing.
``Definitive trials show that consuming less salt lowers blood pressure, and other randomised trials show that lowering blood pressure lowers the risk of heart disease and stroke,'' Neal says.
``What we haven't got are definitive trials that show lowering your blood pressure through salt lowers the risks (of heart disease and stroke).''
But that is the conclusion many experts, Neal included, have drawn.
Nowson says cutting salt by a third has a dramatic impact on your long term health prospects.
``By reducing your salt intake from 9 grams a day to 6 grams a day you reduce the risk of stroke by 22 per cent, and you reduce the risk of coronary heart disease by 16 per cent,'' she says.
A study by Neal, presented at the Meeting of the American College of Cardiology in Atlanta earlier this year, tracked 600 people in rural China who eat virtually no processed food. Half were given a salt replacement, while half were given regular salt to use in all their cooking. At 12 months the mean systolic blood pressure was 5.4 mmHg lower in the group who had been using the salt substitute.
``That is about the same as what drugs do _ it reduces your chance of stroke or heart attack by 25 per cent,'' Neal says.
Meanwhile, professor Michael Alderman, who co-authored the studies in the AJM and Hypertension, says he is not questioning the well documented link between blood pressure and salt _ but says health professionals need to weigh the potential negative effects a low-sodium diet may have against the benefits of lowered blood pressure.
``I guess it's like alcohol _ there's no question about whether or not alcohol increases blood pressure. We know it does,'' he says.
``But we also know that if you drink moderately it makes you live longer, we think, too.''