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30 March 2023

How Does Salt Impact My Blood Pressure?

How Does Salt Impact My Blood Pressure

Dr Katie BlogWritten by Dr Katie Stephens, GP

Dr Katie graduated from the University of Manchester in 2007 (MBChB) and completed her GP training in the West Midlands in 2012 (MRCGP). 

 

Diets that are high in salt increase the risk of having high blood pressure. High blood pressure can cause strokes, heart disease (including heart attacks) and kidney disease. If you have hypertension (the medical diagnosis of persistently high blood pressure), you may be able to improve your blood pressure by cutting down on salt.

How does salt affect blood pressure?

Salt contains sodium. In fact, table salt is essentially made up of two things – sodium and chloride. We know that excess salt can cause high blood pressure. How this exactly happens isn’t known for sure, although there are many scientific articles that have been published with ideas and evidence for different theories. Here is a short summary of two of these theories:

  • Salt can increase the stiffness in the arteries. The arteries are the blood vessels that carry blood away from the heart to the rest of the body. Normally their walls are quite stretchy and elastic. If the heart needs to beat harder, the artery walls can stretch more, giving the blood more space, thereby lowering the blood pressure. Increased salt may damage the artery walls, making them more stiff. If they are stiff, they can’t stretch when needed, and the blood can’t get the extra space it needs. This leads to a raised blood pressure.
  • More sodium in the diet leads to more sodium in the blood. Normally, the kidneys work to get rid of any extra sodium. Sometimes they aren’t able to do this as well, for a number of possible reasons. Having a higher sodium level in our blood may do two things:
    1. It can make us feel thirsty, and drinking more might increase our blood pressure. 
    2. It causes an increase of a hormone called angiotensin II. This hormone is able to raise the blood pressure so effectively, that it is actually the target for two different types of blood pressure lowering medication.

How quickly does salt affect blood pressure?

This depends how much salt is eaten. Small amounts of sodium (2 – 5 mmol/L, which is equivalent to 46 – 115mg) may take days to have an effect. Larger amounts (15 mmol or more, or 345mg) may cause an increase in blood pressure within an hour

For comparison, half a teaspoon of salt has 1150mg of sodium. A can of baked beans has about 2600mg of sodium. A small bag of salt & vinegar crisps has about 400mg. So, even a small bag of crisps would be considered as having a ‘large amount’ of sodium and could increase one’s blood pressure within an hour.

What is salt sensitivity?

Having lots of salt in the diet seems to only raise blood pressure in some people, not everyone. How much the blood pressure rises might also vary – some people might have a very high increase, and others might only have a little increase. One study published in 2021 suggests that about 3 out of 4 people will have at least some level of salt sensitivity.

Even for those people whose blood pressure doesn’t appear to be affected by salt, it can still be helpful to avoid a diet high in salt. This is because excess salt can cause damage elsewhere in the body.

Himalayan salt and high blood pressure

You may have heard about health benefits of Himalayan salt (or pink salt). However, please remember that all salt, no matter the colour or origin, contains sodium and chloride. The amount of sodium is going to be more or less the same, no matter the colour or the name of the salt. It is the excess sodium in the diet that causes blood pressure to rise. So Himalayan salt, like any other salt, still has similar amounts of sodium and can still cause high blood pressure.

Will cutting out salt lower blood pressure?

For most people, reducing the amount of salt in the diet can lead to a lower blood pressure. Generally, we all need a little bit of sodium each day, but probably only less than 500 milligrams. Salt can be naturally occurring in small quantities in healthy foods such as vegetables, fruit, grains and unsalted nuts.

The average person’s diet actually has about 3,400mg of sodium daily – roughly seven times more than we need! Reducing salt intake, even by just a little, and even for those whose diets aren’t particularly high in salt, can reduce both the systolic and diastolic blood pressure.

One way to reduce dietary sodium intake is to follow the DASH diet. The DASH diet (Dietary Approaches to Stop Hypertension) can be an effective way of reducing salt and also lowering blood pressure. It is often ranked as a top diet for it’s health and heart benefits. The diet is flexible and makes the following daily recommendations:

  • 6 – 8 portions of whole grains
  • 4 – 5 portions of fruit
  • 4 – 5 portions of vegetables
  • 2 – 3 portions of mostly low or non fat dairy
  • 6 or fewer portions of lean meat, fish or poultry
  • 4 – 5 portions of nuts, seeds and legumes per week
  • Limited fats and sweets 
  • Limiting sodium to 2,300 mg/day; where appropriate, it states that limiting to 1,500 mg/day is even more effective at lowering blood pressure

The DASH diet promotes healthy, balanced eating including the main food groups, as described above. It can also help aid weight loss, lower cholesterol levels and reduce the risk of diabetes.

How can I lower my salt intake?

Apart from making generalised changes to what you eat like you might with the DASH diet, here are three further ways to reduce your salt intake:

  1. Avoid or limit foods high in salt, such as crisps, processed meats, cheese, microwave meals and takeaways.
  2. Look for and use the traffic light labels on foods when buying groceries. Pick foods that are ‘green’ for sodium content.
  3. When cooking at home, try replacing salt with herbs or other salt-free seasonings. Limit soy sauce also, as this is high in salt.

What are signs of too much salt?

Apart from causing high blood pressure, having too much salt in your diet might also cause the following symptoms:

  • Excessive thirst
  • Bloating
  • Fluid retention
  • Nausea
  • Excessive urination

The above symptoms can also be due to other possible causes, such as high sugar levels. If you are concerned about any symptoms that you have (especially if you have excessive thirst and urination), please seek appropriate medical attention.

Why does high blood pressure matter?

High blood pressure can cause strokes, heart disease (including heart attacks) and kidney disease. It doesn’t usually cause symptoms, and there are over 5 million adults in England with high blood pressure that don’t even know they have it.

Many times, high blood pressure is picked up when someone visits their doctor or nurse for another reason, and the clinician asks to check their blood pressure. With so many appointments now being offered remotely, it is more important than ever for each person to take the initiative to know what their own blood pressure numbers are.

If you haven’t had your blood pressure checked recently, please get it checked soon. You can do this for free at many pharmacies and gyms, book an appointment with the practice nurse at your NHS GP Surgery, or pick up an inexpensive blood pressure machine. If you are buying a personal machine, please ensure it is BIHS approved – that way you know that the numbers it gives you are trustworthy. Pop your reading into our blood pressure calculator to get feedback on your numbers.

Are there any people who shouldn’t cut down on salt?

This article has talked a lot about the benefits of salt reduction. However, it is worth noting that there are two main groups of people who shouldn’t restrict their salt intake:

  1. People who suffer from low blood pressure. For these people, having some salt in the diet can prevent the blood pressure dipping too low. When the blood pressure is very low, it can cause symptoms of lightheadedness and even cause fainting. People with certain medical conditions associated with low blood pressure may be advised to increase their salt consumption.
  2. Pregnant women. While it is still potentially harmful for pregnant women to have too much salt in their diet, it can also be harmful for them to have too little salt in the diet. Too little salt may cause problems with the baby’s growth and can even reduce birth rates. It may also increase the risk of high blood pressure and other medical problems when the baby grows up. Generally, it’s best for pregnant women to find a middle ground when it comes to salt in the diet, unless they have been advised otherwise by their Obstetrician.

The average person has far more salt in their diet than their body needs. All types of salt, no matter the colour or country of origin, contain sodium. Too much sodium can increase the blood pressure. It probably does this through it’s effects on the kidneys, hormones and blood vessels. Having a high blood pressure increases the risk of serious conditions like stroke, heart attack and kidney disease. Although not everyone is sensitive to the effects of salt, it does seem to affect most people at least a little, and affects some people quite a lot. If you have low blood pressure, or are pregnant, it’s best to avoid a low-salt diet. For everyone else, even if you don’t have a lot of salt in your diet, reducing your salt intake will probably lower your blood pressure. Following a healthy, balanced diet, like the DASH diet, might also bring other health benefits as well.

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