Risks of slashing sodium levels in cheese could outweigh benefits, US researcher

Article by Peta Bee

Posted by Mike Pusey, 26 March 2012 - 10:30 GMT

Is salt really the Devil's ingredient?
The Government wants us to reduce our sodium intake, but studies show that this advice should be taken with a pinch of salt

Peta Bee
Salt: is your food full of it? That is the question posed by Jenny Eclair in the Food Standards Agency's recent TV ad for its latest salt awareness campaign. Salt, we are told, pervades every aspect of our diet, from the bowl of cereal we had at breakfast, to the sandwich we ate at lunchtime to the takeaway curry we’re planning tonight.
Too much of the white stuff will our raise blood pressure and increase the likelihood of heart disease and strokes. Like its evil twin, saturated fat, it seems logical that our goal should be to cut down on it, but now a growing number of experts claim that salt is not the devil’s ingredient we have been lead to believe it.
This month researchers from the department of nutrition at the University of California found compelling evidence that it may even be difficult to consume too much salt. Professor David McCarron measured salt losses in the urine of almost 20,000 people in 33 countries worldwide and his findings indicated that the complex interplay between our brains and organs naturally regulates salt intake.
Reporting in the Clinical Journal of the American Society of Nephrology, Professor McCarron said: “It is unrealistic to attempt to regulate sodium consumption through public policy when it appears that our bodies naturally dictate how much sodium we consume to maintain a physiologically set normal range.”
What we do know from other research is that eating less salt will lower blood pressure and cardiovascular risk in people with existing hypertension, but critics argue that for the rest of the population the advice on salt consumption should be taken with, well, a pinch of salt.
While some studies show that people who reduce their daily intake by 1g-2g find that their blood pressure falls, others reveal that huge swings in salt consumption have little effect, with a few showing that blood pressure actually rises.
Among those now questioning the demonisation of our favourite seasoning is Catherine Collins, chief dietician at St George’s Hospital in London, who believes the current pressure to restrict salt in the diet as much as possible is unnecessary and potentially risky.
“The issue has been blown out of proportion,” Collins says. “Salt reduction is very important for people who already have raised blood pressure, but for most people who don’t have hypertension, there is no real benefit to be had from making huge efforts to cut down. It is certainly is not the dietary outcast it is portrayed to be.”
This a view is shared by Michael Alderman, a professor of medicine and epidemiology at the Albert Einstein College of Medicine in New York and a past president of the International Society of Hypertension, who has spent years researching the effects of salt on health. “Only one rigorous, randomised clinical trial on salt intake has been reported so far,” Alderman says. “As it turned out, the group that adhered to a lower sodium diet actually suffered significantly more cardiovascular deaths and hospitalisations than did the one assigned to the higher sodium diet.”
Salt — sodium chloride — is an element essential for health. Every cell in the body needs sodium to function — it is required to regulate fluid balance and for nerves and muscles, such as those in the heart, to function well. Too little salt can cause mental confusion, an inability to concentrate and, in extreme cases, the potentially fatal condition hyponatraemia, which leads to body salts becoming dangerously diluted and the brain swelling beyond the skull’s capacity.
Not that salt depletion is a risk for the average Briton. Although intake has fallen as food manufacturers have begun to add less salt to food, the latest figures from the Food Standards Agency (FSA) show that the average person still consumes 8.6g of salt a day — that’s 0.9g less than in 2000-01, but, not low enough for the FSA. Its long-term goal is to have everybody cut salt to 6g a day.
In theory, this will prevent strokes and heart attacks by lowering blood pressure. What divides experts is whether mass salt avoidance will make much of a difference to statistics on cardiovascular health.
Alderman says that, to date, most of the studies on salt-lowering have been observational, in which the diet habits of different groups are analysed to find any correlation between salt and heart health. Many of them have produced mixed results.
In research conducted at Loyola University in Chicago earlier this year, for instance, Dr Paul Whelton, the president of the university’s health department, followed nearly 3,000 patients for 10-15 years to find out whether the salt they ate had an impact on blood-pressure readings.
After measuring the amount of salt in the urine of his subjects to assess their consumption levels, Whelton found that whether they had used the salt shaker liberally or not did not appear to make any significant difference to their risk of heart disease.
What mattered more, Whelton reported in the Archives of Internal Medicine, was the ratio of salt intake to that of potassium, another dietary mineral (found plentifully in foods such as bananas, avocado, sweet potato and tuna) that is known to balance out the artery-tightening effects of sodium.
An earlier report published in the British Medical Journal in 2002 reviewed the evidence on whether salt avoidance could lower blood pressure and found that, while it was helpful to those on medication for hypertension, there were no clear benefits for anyone else.
Similarly, when researchers from Copenhagen University reviewed the available literature for the Cochrane Collaboration in 2003, they concluded “there is little evidence for long-term benefit from reducing salt intake”.
In fact, Alderman says that of nine observational studies looking at a total of more than 100,000 people, four papers found that reduced dietary salt was associated with an increased risk of death and disability from heart attacks. “In one that focused on obese people, more salt was associated with an increased risk of cardiovascular death,” he says. “But in the remaining four no association was seen.”
However, for those advocating salt cuts — and they remain the majority — the evidence against high-sodium diets is clear.
Graham MacGregor, professor of cardiovascular medicine at St George’s Hospital and chair of the Consensus Action on Salt and Health (CASH) dismisses the negative take on salt reduction as “balderdash” claiming that such findings
are “usually put out by the food industry” to bolster their own cause.
“From the day you are born, your blood pressure starts to go up slowly,” MacGregor says. “Salt is a major factor in that and high-salt diets are the main reason why blood pressure rises with age. And more deaths are linked to raised blood pressure than anything else.”
Precisely how salt raises blood pressure is not entirely clear. It is thought that when salt intake is too high, the kidneys to pass it all into the urine and some ends up in the bloodstream. This then draws more water into the blood, increasing volume and pressure.
MacGregor says that reducing salt to the 6 gram daily levels recommended by the FSA could lead to a 16 per cent reduction in deaths from strokes and a 12 per cent reduction in deaths from coronary heart disease.
“The evidence that links salt to blood pressure is as strong as that linking cigarette smoking to cancer and heart disease,” he says. “If successful, the reduction to 6 grams a day would have the biggest impact of any public health campaign ever.”
Everybody could do with cutting down. In 2008, MacGregor and his colleagues published a study in the Journal of Human Hypertension, which looked at the salt intakes of 1,658 people aged 7 to 18 in the UK. They found salt to be responsible for raising blood pressure in children.
Once more, though, the findings were disputed. In an accompanying editorial, Professor Alderman questioned the link, pointing out that those who ate more salt merely ate more food. Adjusting for calorie intake, Alderman suggested, wiped out the significance of the relationship.
So where does this leave a nation that is being urged to become more salt-savvy? If we scrutinise food labels for their salt content we may live longer. But we may not.
Collins advises against becoming preoccupied with totting up daily salt scores and says she increasingly encounters people whose serum sodium levels have dipped to a dangerous low. “Extreme dieters and vegetarians seem to be most at risk,” she says. “Salt occurs naturally in many of the foods they avoid such as cheese and meat. Since these people are often also drinking copious amounts of water because they think it’s healthy, they often display early signs of hyponatraemia, all linked to their low salt intake.”
In countries where populations are given free access to salt, people typically consume about 5g-8g a day. “A lot of people could relax about their salt intake. If you don’t have hypertension to begin with, then just trying to eat healthily will ensure you don’t get too much,” Collins says. “Advice to cut back on salt really is the poorest of all the dietary messages around.”
Recommended daily salt intake
0-6 months 1g
7-12 months 1g
1-3 yrs 2g
4-6 yrs 3g
7-10 yrs
5g 11-14 yrs 6g
Adults 6g

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