Are salt reduction efforts reflected in heart health?
The premise of salt reduction strategies has been that cutting salt cuts blood pressure, which is a major risk factor for heart disease, stroke, and many other health conditions. However, there are plenty of critics, who argue that just because X leads to Y, and Y leads to Z, that doesn’t necessarily mean that X (high salt intake) leads to Z (higher risk of heart disease and stroke).
The UK’s salt reduction programme is consistently held up as an example for other global initiatives. With about three-quarters of salt consumption coming from packaged foods, its voluntary targets for food manufacturers have helped cut average UK salt intakes from 9.5 g per day in 2002 to about 8.1 g per day in 2014.
After ten years of the UK’s campaign, a study published earlier this year suggested that there was indeed a link between salt reduction, lower blood pressure, and deaths from heart disease and stroke. It looked at data on these factors for 30,000 English people from 2003 to 2011 and found average adult blood pressure fell 3/1.4 mm Hg. Meanwhile, mortality from stroke fell 42%, and heart disease, 40%.
‘Likely an important contributor’
Even after controlling for increased fruit and vegetable intake, blood pressure treatment and alcohol consumption, among other factors, lead author Dr Feng He said the findings suggested population-wide salt reduction “is likely an important contributor to the falls in BP [blood pressure]”.
In Finland, where a salt reduction campaign began in the 1970s, average consumption of salt fell by about a third over 30 years, to about 7 g a day for women and 8.3 g a day for men. According to a 2006 study published in Progress in Cardiovascular Diseases, during the same time period, average blood pressure (both systolic and diastolic) fell by more than 10 mm Hg, and there was a 75% to 80% decrease in both stroke and coronary heart disease mortality in Finland.
However, the suitability of population-wide salt reduction continues to attract debate, as critics continue to say that correlation does not prove causation.
‘Other risk factors’
In particular, a major review of 167 randomised controlled trials published in the Cochrane Library and the American Journal of Hypertension in 2011 challenged salt reduction policy. The Danish researchers found that although cutting sodium consumption did decrease blood pressure, it also tended to increase levels of hormones, cholesterol and triglycerides, which are all thought to be risk factors for heart disease too.
Commenting on the Finnish data, Dr Larry Appel, director of the Welch Center for Prevention, Epidemiology and Clinical Research at Johns Hopkins Medical Institutions, said it was hard to reconcile existing data with the idea that salt reduction might be harmful.
“I can’t attribute all of the benefit to sodium reduction, but again it is hard to believe that there would be a net benefit from the intervention if indeed sodium reduction were harmful,” he told FoodNavigator.
Meanwhile, most people consume far more salt than the 5 g daily upper limit recommended by the World Health Organisation – an average of 8 g to 12 g in Europe.