The relationship between salt and blood pressure.
Posted on December 30th, 2012

Dr Hector Perera       London

When it comes to eating and drinking during the holidays, it’s easy to over indulge with some of your favourite traditional meals, desserts and drinks. A few lucky people have gone back to Sri Lanka during this time of the year to see the parents, families and friends with lots of presents to celebrate Christmas and New Year. They find any excuse to eat and drink such as Christmas then New Year. Once you are there, very likely you will be invited to too many places for lunches, dinners, weddings, birthday parties and for weekend get together. Another important thing to keep in mind is that it’s not the food that matters, but rather the friends and family you eat it with. Unless you control yourself the eager not to over indulge in eating and drinking, no one else can do.

The amount of salt you eat has a direct effect on your blood pressure. Salt makes your body holds more water. If you eat too much salt, the extra water stored in your body raises your blood pressure. So, the more salt you eat, higher the blood pressure.

That means higher the blood pressure, greater the strain on your heart, arteries, kidneys and the brain. The medical reports say, “This excess salt intake can lead you to heart attack, strokes, dementia and kidney problems.” Did you know that 80% of the salt you eat everyday is “hidden” in the processed foods you eat? The processed food packets have clearly marked about salt but many people unlikely read the ingredients, just ignore if the price is right.

Osmosis can be defined as the movement of water across a semi-permeable membrane from a region of high water concentration to a region of low water concentration. The semi-permeable membrane allows small particles through it but does not allow large particles such as sodium chloride. When there is excess salt in the blood, water enters the blood due to osmosis that means the water content increases the volume of blood. Osmosis will continue until a state of equilibrium is reached i.e. there is no area with a higher or lower concentration than another area. No wonder one feels so thirsty when one eats salty food such as crisps, salted cashew nuts and peanuts.
 Maintaining water balance in the kidney can be inhibited by a diuretic, a substance that causes the kidneys to allow excess water loss.  If you don’t replace the lost water, you can easily become dehydrated in a matter of hours.
A very common diuretic is caffeine. Ingesting caffeine all day long can interrupt your sleeping patterns. The residual stimulant from your last caffeinated beverage may keep you from falling asleep at your usual bedtime and can keep you from entering a deep sleep. The lack of sleep will make you groggy the next morning, inducing you to wake yourself up with coffee or a soda.

It is very easy to become addicted to caffeine as it becomes part of your daily routine. If you don’t feed your addiction, you may experience withdrawal symptoms, such as headaches, fatigue and irritability. Most of us always prefer a cup of coffee in the morning.

Diuretics block the production of the hormone vasopressin, an anti-diuretic hormone (ADH).  When the blood has a high concentration of sodium ions, the hypothalamus and pituitary gland (both in the brain) triggers the release of ADH which would tell the kidneys to reabsorb more water to help rehydrate the body.  This is an example of maintaining homeostasis with the endocrine system.  The endocrine system is made up of glands and cells that release chemical messengers called hormones, directly into the blood stream.

What is salt?

Salt is a substance made up of two elements sodium and chlorine, found everywhere, there are seven seas full of salt water. Both elements are essential for life but in very low quantities. Sodium chloride has excellent preservative properties and is commonly used in foods to extend shelf life. We get many Sri Lankan ready to eat food in bottles, cans and in packets, what about the dry fish, sprats and Maldives fish, they are too salty foods. Now these products are not only found in Asian shops but found in plenty in many leading supermarkets in a section called world foods.

However, since the introduction of canning and refrigeration the need for salt to keep food fresh has reduced. Salt is now, all too often, added unnecessarily to our food by food companies as a cheap way to add flavour and bulk to meat. This has lead to us eating a lot more salt than we need and becoming accustomed to the taste.

What we can do is not to add salt when cooking or at the table; use pepper, herbs, spices and lemon juice instead to flavour the food. Rock salt, sea salt and garlic salt are just as bad for you as table salt because they all contain sodium chloride.

The doctor’s advice to have regular blood pressure checks to monitor your progress but the question is how many people cared to check the blood pressure? The next question is why, is the answer, too busy?

Salt and your health

Evidence has shown that a number of health conditions are caused by, or exacerbated by, a high salt diet. Although the strongest evidence is for the effect that a high salt diet has on blood pressure, stroke and heart disease, there is also a wide body of evidence indicating a link between salt consumption and other conditions.

Salt has been linked to:

High Blood Pressure, cardiovascular disease (stroke, heart disease and heart failure), kidney disease & kidney stones, obesity, osteoporosis, stomach cancer, water retention/bloating.

Salt is also thought to exacerbate the symptoms of a few other illnesses and some of them are diabetics, Meniere’s disease, asthma and Alzheimer disease.

Hypertension and Diabetes

The people with diabetes have an increased risk of high blood pressure, says the American Diabetes Association, because excess sodium in your diet causes blood pressure to rise that means whether type one or type two diabetic people could develop high blood pressure or hypertension with the consumption of excess salt in the diets. Common table salt contains 40 percent sodium, an essential mineral your body uses in small amounts for maintaining fluid balance. Managing blood pressure is crucial for diabetics because diabetic hypertensive patients develop coronary artery disease or an enlarged heart more commonly than people with singular hypertension or diabetes, according to a 2008 review in “Advances in Cardiology.” Additionally, high dietary salt intake in diabetics may have a causative role in higher mortality rates; research is ongoing to identify the specifics of the mechanism of action.

Blood pressure readings vary, but in general your blood pressure should not go above 130/80. The first, or top, number is the “systolic pressure” or the pressure in the arteries when your heart beats and fills the arteries with blood. The second, or bottom, number is the “diastolic pressure” or the pressure in the arteries when your heart rests between beats, filling itself with blood for the next contraction.

Current salt intake & dietary advice

Almost everyone in the UK (and the rest of the Western world) eats too much salt. The daily recommended amount in the UK is no more than 6 grams a day; the current average salt intake is 8.6g salt a day although many people are eating more than this.

People with or considered at risk of high blood pressure should take extra care to ensure that they keep their salt intake below the recommended maximum of 6g. This can be achieved by simple changes, such as consuming less processed foods and checking product labels before purchase.


Salt and blood pressure

While some evidence suggests that obesity coupled with a lack of exercise is an important factor involved in the development of high blood pressure, stronger evidence indicates that salt intake is more strongly related to the development of hypertension, particularly the rise in blood pressure with age. Hypertension can be defined as a blood pressure of 140/90 mmHg or higher. However, the risk of cardiovascular disease increases throughout the range of blood pressure starting from a systolic blood pressure of 115mmHg which 80% of the adult population exceeds. Let me remind again, the first, or top, number is the “systolic pressure” or the pressure in the arteries when your heart beats and fills the arteries with blood. The second, or bottom, number is the “diastolic pressure” or the pressure in the arteries when your heart rests between beats, filling itself with blood for the next contraction. Raised blood pressure is the major cause of the development of cardiovascular disease, and accounts for 60% of all strokes and 50% of all heart disease. Blood pressure is the biggest cause of death in the world through the strokes and heart attacks it causes.  Approximately one in three adults in the UK, 16 million adults, has high blood pressure. Five million people don’t know they have the condition yes, they have not checked the blood pressure. They may do normal work; even go shopping with this condition. Unless they check their health no one forces to do so until something happens. They just eat, drink and smoke without knowing they are suffering from high blood pressure.

Anyone is at risk of a high blood pressure, as blood pressure starts to increase from childhood. Research found out that the people with a high salt diet, pregnant women and people of black African descent are particularly susceptible to high blood pressure. The reason is there is a gene that is responsible but cannot be easily identified. Very likely in the future this would be identified and finds a cure for high blood pressure.

How does salt contribute?

A high salt diet disrupts the natural sodium balance in the body. This causes fluid retention which increases the pressure exerted by the blood against blood vessel walls (high blood pressure). For every one gram of salt we cut from our average daily intake, there would be approximately 6,000 fewer deaths from strokes and heart attacks each year in the UK.  It has been estimated that a reduction in salt intake from 10g a day to 6g will reduce blood pressure and could lead to a 16% reduction in deaths from strokes and a 12% reduction in deaths from coronary heart disease. This would prevent approximately 19,000 stroke and heart attack deaths in the UK each year and 2.6 million each year worldwide.  Reducing salt is one of the quickest ways to reduce your high blood pressure, particularly if you already have high blood pressure.

A large number of studies have been conducted which have consistently shown that salt intake is the major factor increasing population with high blood pressure. The evidence is greater for the effect of salt on blood pressure than any other dietary and lifestyle factors including a low consumption of fruit and vegetables (i.e. low potassium intake), obesity, excess alcohol intake and lack of physical exercise.

A large study of 52 communities throughout the world – the Inter Salt Study “”…” has also been conducted by taking standardised measurements of blood pressure and 24 hour urinary sodium and potassium. The study showed a positive relationship between salt intake (using 24 hour urinary sodium excretion) and blood pressure. There was also a positive and highly significant relationship between salt intake and the increase in blood pressure with age. This relationship showed that an increase of 6 grams of salt per day over 30 years would lead to an increase in systolic pressure by 9 mmHg. This represents a large increase in population blood pressure.

Two studies both 4 weeks in duration have compared the effect of different salt intakes on blood pressure 12 g/day in one and 8 g/day in the other. Both showed a clear dose-response relationship, i.e. the lower the salt intake achieved, the lower the blood pressure. 

The most recent meta-analysis focusing on salt and blood pressure looked at 28 randomised trials in hypertensives, in normotensives (normal blood pressure)) with a duration of one month or longer. It showed that a modest reduction in salt intake led to a significant reduction in blood pressure, both in people with and without high blood pressure.  A dose-response relationship between the reduction in salt intake and the decrease in blood pressure was also seen. It is estimated that a reduction of salt by 6 g/d would lower blood pressure by 7/4 mmHg in individuals with high blood pressure and 4/2 mmHg in those with normal blood pressure.

The relationships seen in these studies provide evidence that the recommendation to reduce salt intake to 5-6g/day will have a major impact on blood pressure and a further reduction to 3-4 d/day will have a much greater effect. That means we need to cut down on salt. Any comments please

2 Responses to “The relationship between salt and blood pressure.”

  1. callistus Says:

    Write to New Scientist or Lancelet

  2. Leela Says:

    Thank you doctor for taking your time to offer us (unconcerned easy going people) with this valuable information.

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