Science: Salt reduction benefits beyond the heart

Salt is of course a vital nutrient and is necessary for the body to function, but the average daily salt consumption in the western world, between 10 and 12g, vastly exceeds recommendations from WHO/FAO of 5 grams per day to control blood pressure levels and reduce hypertension prevalence and related health risks in populations.

And with 80 per cent of salt intake coming from processed foods, many countries have initiated salt reduction programmes, with many holding up the UK’s Food Standards Agency as the torch bearer for national initiatives.

The benefits of a salt global salt reduction strategy were given blinding clarity by a meta-analysis published in The Lancet Chronic Diseases Series​ in 2007, which concluded that reducing salt intake around the world by 15 per cent could prevent almost nine million deaths between 2006 and 2015.

While the majority of the science has looked at the potential of reduced salt to reduce the risk of developing hypertension, with the ultimate aim of reducing the risk of cardiovascular disease, the benefits of salt reduction may extend beyond heart disease.

Stroke​

With high blood pressure being the biggest contributing factor for stroke, it will come as no surprise that studies have examined a link between salt intake and stroke.

A meta-analysis by Dr Feng He and Professor Graham MacGregor from the Blood Pressure Unit at St. George's, University of London reported in 2002 that cutting daily salt intake by six grams may cut stroke by 24 per cent and coronary heart disease (CHD) by 18 per cent (Journal of Human Hypertension, Vol. 16, pp. 761-770).

Such a reduction would translate into a global reduction of about 2.5 million deaths, added He and MacGregor a year later (Hypertension​, 2003, Vol. 42, pp. 1093-1099).

Kidneys​

Increased salt intakes have also been linked to kidney health, with studies focusing on albumin levels. Microalbuminuria occurs when small amounts of albumin – the most abundant protein in human serum - leaks from the kidney into the urine. It is a marker of early kidney disease development.

Montpellier, France-based scientists reported that increased blood pressure, associated with salt intake, increased kidney damage, as measured by increased amounts of urinary protein or albumin (American Journal of Hypertension​, 2002, Vol. 15, pp 222-229).

Stomach damage​

The link between salt intake and stomach cancer has been reported in several studies, and centres on the role of Helicobacter pylori​ - the only bacteria that can survive in the acidic environment of the stomach and known to cause peptic ulcers and gastritis.

Infection with H. pylori​ also causes gastritis, and infected persons are said to have a two to six-fold increased risk of developing mucosa-associated lymphoid tissue (MALT) lymphoma, and gastric cancer compared with uninfected counterparts.

According to the World Action on Salt and Health (WASH), studies from 2004 (Journal of Hypertension​, Vol. 22, pp. 1475-1477) and 2008 (Asia Pacific Journal of Clinical Nutrition​, Vol. 17, pp. 644-650) reported that salt may increase the growth and action of H. pylori​, thereby raising the risk of stomach cancer.

Furthermore, a Japanese study from 2006 reported that salt may play a role in the irritation and inflammation of the stomach lining (International Journal of Cancer​, Vol. 119, pp. 196-201).

Bones​

A recent study from Australia reported that salt reduction may also have benefits for bone health in women at risk of osteoporosis – a condition described by the World Health Organisation as its biggest global healthcare problem.

Writing in the British Journal of Nutrition ​(2009, Vol. 102, pp. 1161-1170), researchers from Deakin University reported that middle-aged women with pre- or stage 1 hypertension assigned to consumed a low-sodium diet experienced reductions in calcium excretion compared to people consuming a high-carbohydrate low-fat diet.

A study from scientists at the Purdue University looked at the effects of salt in adolescent girls. Their results, published in the American Journal of Clinical Nutrition​ (2005, Vol. 81, pp. 845-850), suggested that Caucasian girls lose more calcium in their urine than African-American girls.

But both races lose calcium at an accelerated rate when they consume a high-salt diet.

“Salt is processed differently in the races, but too much salt in the diet reduces bone density in both races,”​ wrote the researchers.

The benefits work in practice ​

While more research is needed to support the benefits of lower salt intakes for bone health and the other health areas, a recent clinical trial showed that moderate reductions do indeed result in clinically relevant and beneficial reductions in blood pressure.

The largest double-blind trial of modest salt reduction in a free-living population, published in the American Heart Association’s Hypertension,​ journal found that reducing salt intake from 9.7 to 6.5 grams per day reduced average blood pressure from 146/91 to 141/88 mmHg within six weeks.

FoodNavigator will continue the salt reduction series tomorrow.