The less salt we eat, the better our health.
High salt diets are strongly linked to high blood pressure – a major risk factor for cardiovascular diseases including stroke and heart attack.
It is widely recognised that a high salt diet has other adverse effects, including being a risk factor for kidney disease and stomach cancer.
Salt may also be implicated as an aggravator of asthma and a contributor to osteoarthritis.
Australian salt intake
The average Australian adult consumes about 9 grams of salt each day. This is far more than our bodies require to be healthy – we can survive on as little as a gram of salt each day.
Australians should reduce the amount of salt they eat to less than 6 grams per day – even further wherever possible. Australians with high blood pressure or an existing cardiovascular disease should reduce their salt intake to below 4 grams per day and even further if possible.
Benefits for children’s health
Eating too much salt can also influence children’s blood pressure and pre-dispose them to health problems in later life. As our capacity to rid our body of excess salt decreases as we age, it is very important to develop healthy habits when we are young.
a man has his blood pressure checkedEvidence shows that eating a low salt diet reduces blood pressure.
How does salt increase blood pressure?
As the salt content of our blood increases, our blood vessels retain water to try to keep the salt concentration balanced. This extra water increases the amount of blood in our vessels causing high blood pressure.
Why is high blood pressure bad for our health?
High blood pressure puts a strain on our blood vessels. It can also damage our heart, which has to work harder pumping blood at such high pressure around our bodies. This damage can lead to heart failure and can increase our risk of having a heart attack or stroke.
Over time, high blood pressure can damage and weaken our arteries. This can cause illness and death, especially if the damaged section bursts in the brain or in the aorta, our main artery.
High blood pressure can also narrow blood vessels (arteries, veins and capillaries) because the walls of the blood vessels thicken and harden due to all the hard work that they are doing to handle the increased pressure. When this happens, the blood flow is reduced. This can damage the organs receiving the blood. A blood clot could also block a narrow artery, cutting off blood supply to part of the body.
As they get thicker and stiffer, our blood vessels also get less elastic. This causes further pressure increases as it means blood is getting pumped into a rigid system that can’t absorb any of the pressure.
Ongoing high blood pressure is the leading risk factor for cardiovascular disease, including strokes, heart attacks, heart failure and arterial aneurysms. High blood pressure is also the second leading cause of chronic kidney failure.
Nearly 30% of Australians have high blood pressure, and over half of these people are unaware that they have it.
Low salt, low blood pressure
There is very strong evidence that links salt intake to blood pressure. Reducing your salt intake will help lower your blood pressure and your risk of health problems such as cardiovascular disease and kidney failure.
A reduction in salt intake of 1.7 grams per day^ results in a 2-5 mm Hg fall in systolic blood pressure. Recent evidence* suggests that a reduction in salt intake of 25 to 35% could lead to a 20% or greater reduction in risk of heart attacks and stroke.
^Summary of evidence statement on the relationships between dietary electrolytes and cardiovascular disease National Heart Foundation of Australia October 2006
*Cook NR, Cutler JA, Obarzanek E, Buring JE, Rexrode KM, Kumanyika SK, Appel LJ, Whelton PK. Long term effects of dietary sodium reduction on cardiovascular disease outcomes: observational follow-up of the trials of hypertension prevention (TOHP). British Medical Journal. 391476048, doi:10.1136/bmj.39147.604896.55
Kidney damage and failure
bread slices14% of Australians have some form of kidney damage.
High blood pressure, caused by salt, contributes to kidney damage because of the harm it does to blood vessels. For the same reason, once kidney damage has occurred, high blood pressure accelerates its progression towards kidney failure.
A kidney stone is a hard mass formed in the kidney from crystals in the urine. Urinary crystals can be caused by high levels of certain substances (such as calcium oxalate or calcium phosphate) in the urine, an uneven balance of acid in the urine, or, a lack of substances that inhibit crystal formation in the urine. Kidney stones may cause pain, nausea, vomiting, fever, chills, weakness, and cloudy, bloody or blocked urine.
A high salt diet may contribute to the likelihood of developing kidney stones due to the relationship between salt and the body’s ability to absorb calcium. Too much salt reduces the body’s ability to absorb calcium, leading to its loss through urine and a greater risk of developing kidney stones.
japanese foodSalt intake is closely related to cancer of the stomach and is likely to be an important pre-disposing cause.
In the high concentrations found in foods such as some instant soups and soy sauces, salt is a profound gastric irritant. It has been suggested that a high salt intake strips the lining of the stomach and may pre-dispose the individual to infection from the Helicobactor pylori bacterium. Long-term Helicobactor pylori infection is considered a major risk factor for stomach cancer – it may lead to chronic inflammation of the inner layer of the stomach and possible pre-cancerous changes in the stomach lining. Keeping our salt intake low may help reduce the risk of cancer of the stomach.
Other Health Problems
nutrition information labelAside from the strong evidence linking high salt intake to high blood pressure, heart problems, cancer and kidney disease, salt has been implicated in some other health issues.
Salt intake has a direct relationship with how much calcium our bodies excrete through urine. The more salt we eat, the more salt we excrete, and the more calcium we excrete along with it.
There is now evidence to suggest that when we excrete too much calcium, our intestinal absorption of calcium increases and our bodies also compensate by using calcium from our bones. This has led some authors to suggest that lowering salt intake could reduce calcium excretion, leading to a positive calcium balance, increased bone density and reduced bone fractures. Studies to test this idea are yet to be conducted.
Bronchial reactivity is linked to sodium balance. There is some evidence to suggest that the severity of asthma may relate to salt intake. There has also been a study that related a modest reduction in salt intake to a reduction of the severity of asthma attacks and an improvement in measurements of airways resistance in males. A more recent study illustrates the mechanism whereby a higher salt intake could exacerbate asthma.
So, while high salt intake is not a direct cause of asthma, it may be an aggravating factor.
Thirst is an unavoidable consequence of eating foods with a high salt content. Where thirst is relieved with high-sugar or high-calorie beverages, such as soft-drinks or beer, it may contribute to weight gain.
Some authors have suggested that increases in salt consumption observed in the USA are strongly associated with increases in obesity there. The conclusion has been drawn that a reduction in salt intake could lead to a reduction in obesity. Salt sales in the USA were reported to have increased more than 50% between the mid-1980s and late-1990s, and these sales were paralleled by an increased consumption of beverages, which led to an increased intake of calories during the same period.
As suggestions of the link between salt intake and obesity gain further scientific support, there is an increasing argument to reduce salt intake as a means of combating the growing epidemic of obesity in Australia.
Ménière’s disease is a condition with symptoms including vertigo, tinnitus, fluctuating hearing loss and a feeling of pressure in the ear.
The disease affects one in every 1000 Australians, most of whom are in their thirties or older.
Although the causes of Ménière’s are not well understood, one of the key strategies in treatment is a strict control of salt intake.
Salt and Children’s Health
Good eating habits in childhood can influence habits and health later in life
Children with higher blood pressure are more likely to develop hypertension as adults than children with lower blood pressure. Although the health problems associated with high blood pressure often don’t appear until later in life, they are strongly influenced by childhood health.
Keeping blood pressure low from childhood is probably the best way to avoid blood pressure-related health problems in later life.
Eating pattern development
Evidence also shows that dietary habits developed in childhood and adolescence can influence eating patterns later in life. Children who develop a preference for lower salt foods are likely to maintain this preference as they get older.