New study finds no connection between salt and heart disease
Another new study is questioning the oft-repeated connection between the consumption of too much salt and the development of cardiovascular disease. The meta-analysis, just published online in the American Journal of Hypertension, examined the results of seven clinical studies and found no solid proof that reducing salt consumption prevents heart conditions.
The World Health Organization recommends that no more than 5 grams of salt per day should be consumed, whereas people in many Western countries typically eat twice as much. Public-health authorities are already looking at ways of cutting the salt content of foods. For instance, Britain’s Food Standards Agency is working with food manufacturers to reduce sodium, and the New York City health department is spearheading a national initiative to cut Americans’ salt consumption by 20% over 5 years. [SA’s health minister recently said his dept would introduce legislation to cut the salt content of processed food]
How might salt cause heart disease?
Consuming sodium causes the body to retain water, thereby increasing blood pressure, and hypertension is a risk factor for heart attack, stroke and other cardiovascular diseases.
A number of clinical trials and meta-analyses have suggested that cutting one’s salt intake reduces blood pressure, says Rod Taylor, a statistician at the University of Exeter, UK, who led the new study. But his team says that it is unclear whether restricting salt intake reduces blood pressure sufficiently to protect against heart disease. A previous meta-analysis found that eating less salt reduced people’s blood pressure — but on average only slightly.
On the other hand, many studies comparing how much salt people consume with their incidence of cardiovascular disease have come up with clearer links. A 2009 meta-analysis3 of 13 such studies, incorporating 177 000 patients, found that a high-salt diet increased the risk of stroke by 23%.
Why has it been so difficult to prove whether or not cutting salt prevents cardiovascular disease?
Observational studies, which look at the correlation between salt intake and the incidence of disease, can’t directly pin reductions in cardiovascular disease on eating less salt, Taylor says. “People are choosing to reduce their salt, but it may be associated with a whole host of other healthy behaviors. They may be more active and eating less saturated fat” — factors that also protect against cardiovascular disease.
“To inform policy and whether we should be advising people to reduce their salt, observational studies do fall short,” Taylor adds. Controlled experimental trials, in which patients are placed on a low- or high-salt diet and followed over time, should offer a clearer answer, he says…..
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Meanwhile, a recent study published in the Journal of the American Medical Association (JAMA) proposes that even modest reductions in salt intake may be associated with an increased risk of cardiovascular disease and death.
The researchers report that people with the lowest levels of sodium in their urine (a marker of salt intake) at the start of the study had a 56% higher risk of dying from cardiovascular disease than people with the highest levels. This certainly contradicts the advice of a majority of health and federal bodies, who have been telling consumers to drastically cut back on their sodium consumption.
In a recent ePerspective post, John Ruff, retired Senior Vice President of Global Quality, Scientific Affairs and Nutrition at Kraft, identifies some key flaws in the JAMA study, which impact the researchers’ findings (see Sensationalism and Salt: JAMA study has many flaws). According to Ruff, although the study quotes a sample size of 3 681, the conclusions about cardiovascular disease (CVD) are based solely on the 84 who died during the study. Another weakness is that sodium intake was only determined for a single day over the course of the study and no calorie or other nutritional data was collected.
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