Salt may be a hidden killer but as health campaigners call for regulations, the picture keeps shifting. Geoff Cumming sifts through the evidence
Give the food police credit for trying. Knocked back on calls for maximum sugar limits, junk food advertising bans and school tuckshop restrictions, some health experts now want a government clampdown on the amount of salt we eat.
A call by the United States Institute of Medicine for the Obama Administration to impose maximum limits for salt content - and progressively lower them - across a vast range of foods is the kind of intervention needed here, say the Stroke Foundation and leading researchers.
Despite quiet moves to reduce salt content by New Zealand and multinational food manufacturers in the last five years, some experts claim a national strategy is needed.
"We don't think leaving it to industry alone will be enough," says Stroke Foundation chief executive Mark Vivian.
"The general public can be sold the message that salt is important as a flavour and a preservative but who is saying 'salt is killing us'? What's the strategy around the health implications of too much salt?"
Too much salt has long been linked to high blood pressure, a leading cause of cardiovascular disease and strokes, along with obesity, smoking and excessive alcohol consumption. Together, heart disease and strokes are our leading killers, responsible for around 32 per cent of deaths each year, ahead of cancer (28 per cent).
Yet salt has escaped the blowtorch applied to saturated fats, sugar, alcohol and tobacco as health watchdogs try to change behaviours to reduce premature deaths and soaring medical costs.
Meantime, changed diets - a trend towards more packaged and processed foods, ready-to-eat meals, more fast food and eating out - lead researchers to suspect our salt intake has gone through the roof.
They already believe our average daily salt intake is at least 50 per cent higher than the safe maximum of no more than 5.8g (just over a teaspoon) a day, and some experts argue the limit should be set even lower. Sampling of 704 blood donors in Hamilton and Dunedin in the 1990s found women were consuming an average 9.2g of salt a day and men 11.3g/day.
The problem is that most of our salt intake comes not from what we sprinkle on to home cooking but from the packaged, processed and ready-to-eat foods we are increasingly buying.
Several recent international studies have highlighted the potential to significantly reduce strokes and heart disease simply by targeting salt. Researchers argue that a national strategy to lower salt levels would be more effective than tobacco control in reducing premature deaths and reducing the billions spent on high blood pressure medication and hospital care. It is seen as a "simple" intervention which would remove the onus from individuals to cut down.
Reducing salt in manufactured food by 25 per cent could result in 2745 fewer heart attacks and 2064 fewer strokes each year (an 18 per cent reduction in both), saving 930 lives a year by 2018, a report in last week's New Zealand Medical Journal says.
The "hidden" sodium in processed foods is responsible for about 85 per cent of daily salt consumption, experts claim. Salt is added for flavour and as a preservative to many foods, including bread, butter and cheese, breakfast cereals, processed meats, canned goods and packaged foods such as "instant" noodles and pastas. While sodium content is listed on the nutritional panels - often in surprising amounts - few consumers appreciate its significance. Salt content also varies considerably between brands.
"A large part of the population may not be aware that salt is potentially quite damaging and those who are aware may not realise how much of their intake comes from cereals and processed foods," says Vivian.
Salt is an insidious ingredient in most diets, he says. "People think of potato chips but don't realise how much salt is in breakfast cereals."
Nor is the problem confined to processed and packaged foods. Sandwich bars, cafes, restaurants and takeaway outlets all rely on salt for flavouring to varying degrees.
Vivian says it has long been held that 20 per cent of New Zealanders have high blood pressure, many of whom are unaware. A "startlingly high" number of those who had their blood pressure checked in an awareness campaign last September had diagnosable levels on the day. Recent Australian data found about 35 per cent of the population had high blood pressure.
The Foundation plans later this year to ask the Ministry of Health and the Government to commit to a salt reduction strategy. It wants mandatory limits set for manufacturers to comply to. Levels would be brought down gradually to avoid a consumer backlash against products.
A mandatory approach may not be expected to gain traction with the National-led Government which last year reversed several of Labour's "nanny state" attempts to tackle diet-related issues such as obesity.
But new data on how much salt New Zealanders are consuming may change thinking. Results from the Food Safety Authority's total diet survey are due later this year while the Health Ministry's 2009 national nutrition survey (due for release in June 2011) could either ease concerns or raise palpitations.
Gathering reliable data on individual sodium levels is difficult, requiring 24-hour urine samples. Researchers concede the average daily consumption estimate of 9-11g may be past its use-by date. Though some suspect intake has increased with consumer trends, recent reductions in sodium content by many food manufacturers may have a significant impact.
Salt content in mass-label breads - our biggest source of dietary sodium - has fallen by up to 20 per cent after an industry-wide initiative led by the Heart Foundation. The Foundation is now working with cereal makers and processed meat firms (see sidebar). Supermarkets have also made big quality improvements to many "house brand" products such as Pam's and Home Brand after a disturbing 2004 study which found lower-priced items generally had much higher sodium levels than more expensive brands (see panel).
But health experts argue the gains are insufficient. Emeritus Professor Robert Beaglehole of Auckland University applauds the bread industry's effort to lower salt content but suspects this has made only a small difference to the overall picture.
Beaglehole, a former director of the World Health Organisation's department of chronic diseases and health promotion, says excessive sodium has been a neglected cause of preventable death and disability.
He says salt is a cheap way of adding taste and suspects it may be used to add weight, as salt absorbs water. He believes some manufacturers haven't thought about how much salt is really needed.
Beaglehole says years of voluntary efforts in the US have not made sufficient progress and regulation would rein in "rogue" manufacturers.
"Let's get serious and encourage the food industry to work to common standards and level the playing field.
"The Government doesn't have to get highly involved but it does have to facilitate the process of setting standards."
His colleague, stroke expert Professor Ruth Bonita, says setting targets to reduce salt levels over time makes economic sense, as it would ease pressure on hospitals and medication costs. She says policies which reduce government health costs while improving health across the population are a "no-brainer".
Heart Foundation medical director Professor Norman Sharpe says considerable progress has been made by working collaboratively with food manufacturers in recent years but the Foundation does not rule out a regulatory approach.
He says the rise of the fast food diet is a real concern as many takeaways are high in both saturated fats and salt. This has a "double whammy" effect on heart health, affecting both cholesterol and blood pressure levels.
The NZ Food Safety Authority last December made salt reduction a priority issue after earlier diet surveys suggested levels were too high. Senior nutrition manager David Roberts says the Authority will monitor trends to see whether voluntary efforts are working.
"You have to give industry groups some credit for front-footing this without a lot of pressure."
Food and Grocery Council chief executive Katherine Rich says those wanting mandatory salt reduction targets are neglecting the progress manufacturers have made. She says multinationals in New Zealand and overseas have invested millions in reducing salt content and "there is only so much salt that can be taken out".
"Once governments start to regulate it's a slippery slope. No government is going to be an expert on what level of salt to put in products."
Rich, a former National MP, was instrumental last year in dissuading the Government from the mandatory addition of folic acid to bread to reduce the incidence of spina bifida, putting New Zealand out of step with Australia. She says New Zealanders will "find themselves eating cardboard" if too much salt, sugar and fat are taken out of processed foods. Salt is a necessary ingredient in many products, including cheese.
"It comes down to a difference in political ideology. There are some who think you can regulate everything, ban everything and that will effect behavioural change. On the other side are those who believe in individual responsibility...
"Ultimately it comes back to New Zealanders thinking carefully about what they eat and aspiring to a healthy diet. Regulation is unlikely to do that."
The call for intervention in the US comes after the Congress asked top science body the US Institute of Medicine to recommend strategies.
The institute concluded that 40 years of voluntary efforts were not doing enough. It recommended the US Food and Drug Administration gradually reduce the maximum level of salt that can be added to foods, with a timeline for achieving guideline sodium levels of no more than 2300mg a day - about a teaspoon of salt.
Within days, food companies announced a partnership with the New York City Health Department to reduce sodium levels by 20 per cent. Multinationals including Heinz, Kraft, and Starbucks signed up to the voluntary strategy, which covers 62 packaged foods and 25 restaurant foods.
In Britain, food makers have reduced salt levels by 40 per cent in some products.
LEADING CAUSES OF DEATH IN NZ
18 per cent Tobacco consumption
17 per cent High cholesterol
13 per cent High blood pressure
11.5 per cent Obesity
3 per cent Alcohol consumption
source: Ministry of Health, 2004