Tuesday, October 27, 2009

Is salt really the Devil's ingredient?

More fad "science": The British Government wants people to reduce their sodium intake, but studies show that this advice should be taken with a pinch of salt

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 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. [An ad hominem argument. The man is no scientist] “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.”


Is DDT bad after all? Boys with urogenital birth defects are 33 percent more common in African villages sprayed with DDT

A .33 difference is insignificant anyway. The Federal Reference Manual on Scientific Evidence, Second Edition says (p. 384): "the threshold for concluding that an agent was more likely than not the cause of an individual's disease is a relative risk greater than 2.0.".

The journal article is "DDT and urogenital malformations in newborn boys in a malarial area" by Riana Bornman et al.. Excerpt: "Of the newborn boys 10.8% (357) had UGBDs; a multivariate logistic model showed that mothers who lived in villages sprayed with DDT between 1995 and 2003 had a significantly greater chance (33%) of having a baby with a UGBD than mothers whose homes were not sprayed".

That is exceedingly weird. The implication is that even in the unsprayed villages, 8% of the kids had defective plumbing. The findings are clearly not generalizable to anything in the Western world. The MAIN cause of the defects has obviously not been identified. When it is, we might be able to see if and how how it interacts with DDT. Maybe the villages that got more DDT also got more of the problem agent, whatever that might be.

Much farting at the mouth by a self-satisfied and self-righteous Prof. Bornman below. A Professor he/she may be but a scientist he/she is not. Academics customarily eschew personal publicity. Prof. Bornman obviously laps it up

Let me see if I can do a better job of scientific interpretation than Prof. Bornman -- using no more than general knowledge. Male genital deformities could be caused by a heavy load of estrogens but Western sources of estrogens are not likely to be found to any extent in African villages. So it must be phytoestrogens at work. But to get a heavy load of phytoestrogens the villagers must be very successful farmers. And wouldn't successful farmers be more likely to be ready, willing and able to take up modern aids to health -- such as DDT? So the "third factor" (the single underlying cause of both the deformities and the high DDT usage) is prosperity, African style. Whether that explanation is right or not, however, it exposes Prof. Bornman's brain-dead attachment to the logical fallacy that correlation is causation
Women who lived in villages sprayed with DDT to reduce malaria gave birth to 33 per cent more baby boys with urogenital birth defects (UGBD) between 2004 and 2006 than women in unsprayed villages, according to research published online by the UK-based urology journal BJUI. And women who stayed at home in sprayed villages, rather than being a student or working, had 41 per cent more baby boys with UGBDs, such as missing testicles or problems with their urethra or penis.

The authors suggest that this is because they spent more time in homes where domestic DDT-based sprays are still commonly used to kill the mosquitos that cause malaria, even in areas where organised mass spraying no longer takes place.

Researchers led by the University of Pretoria in South Africa studied 3,310 boys born to women from the Limpopo Province, where DDT spraying was carried out in high-risk areas between 1995 and 2003 to control malaria. The study compared boys born to women in the 109 villages that were sprayed, with those born to women from the 97 villages that were not. This showed that 357 of the boys included in the study – just under 11 per cent – had UGBDs. The incidence of UGBDs was significantly higher if the mother came from a sprayed village.

"If women are exposed to DDT, either through their diet or through the environment they live in, this can cause the chemical to build up in their body" explains lead author Professor Riana Bornman from the University's Department of Urology. "DDT can cross the placenta and be present in breast milk and studies have shown that the residual concentration in the baby's umbilical cord are very similar to those in maternal blood.

"It has been estimated that if DDT exposure were to cease completely, it would still take ten to 20 years for an individual who had been exposed to the chemical to be clear of it. Our study was carried out on boys born between 2004 and 2006, five to nine years after official records showed that their mothers had been exposed to spraying. "Records were not kept before 1995 in the Limpopo Province, but it is reasonable to assume that DDT was being used before that date to combat malaria.

"Although most countries have now banned the use of DDT, certain endemic malarial areas still use indoor residual spraying with DDT to decrease the incidence and spread of the disease, which is caused by mosquitoes."

The two-year study included 2,396 boys whose mothers had been exposed to DDT and 914 whose mothers had not. A number of other factors were taken into account to rule out possible causes of the birth defects. These included smoking and drinking, the mother's age, how long she had lived in her village and her race. These all proved statistically insignificant.

The authors believe that their study highlights the importance of educating people in high-risk malaria areas about the dangers of DDT. "The use of DDT has contributed to the success in reducing malarial transmission and malarial deaths in South and Southern Africa" says Professor Bornman. "However, the present findings also strongly suggest that indoor residual spraying with DDT is associated with UGBDs in newborn boys. "With global concerns about the effect of chemicals on health, and the possibility of malaria resurgence and spread as a result of climate change, all authorities should ensure that the general public, including those living under indoor residual spraying conditions, are aware of the possible health risks.

"Educating people living in the DDT-sprayed communities about ways of protecting themselves from undue DDT exposure needs to be carried out as a matter of extreme urgency. "There must be long-term monitoring of possible environmental and human health impacts, particularly in those areas where DDT will be introduced as part of the fight against malaria. "We are now carrying out further research to find out how indoor spraying using DDT-based products affects humans and how this risk can be reduced."


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