Hypertension: Does reducing your salt intake help?

Reducing your salt intake can help lower blood pressure in the medium term: one spoon of salt less per day could make a difference. It is not clear how this affects the long-term risk of complications or the use of medication.

If someone has hypertension (high blood pressure), their blood vessels are exposed to increased pressure. Although this does not necessarily cause noticeable symptoms, over the years it can damage the heart and the blood vessels, leading to health problems. This means that cardiovascular (heart and circulation) diseases like heart attacks and strokes are more common in people who have high blood pressure. In Germany, almost half of all adults have hypertension, and it is slightly more common in men than in women. Most people who have high blood pressure have what is known as essential hypertension. This means that there is no known underlying medical condition causing it.

Blood pressure readings consist of two measurements: an upper measurement called the systolic blood pressure, and a lower measurement called the diastolic blood pressure. Your systolic blood pressure is the higher pressure on your vessels when your heart muscle squeezes to pump blood into your body. The diastolic blood pressure is the lower pressure in your circulation when your heart muscle is relaxing and the heart is filling up with blood again. People are considered to have a high blood pressure if the upper measurement is over 140 mm Hg, if the lower measurement is over 90 mm Hg, or if both measurements are high. So a blood pressure reading of 180/100 mm Hg is very high, for example. The unit of measurement “mm Hg” stands for “millimeters of mercury”.

It is important to measure people’s blood pressure in a calm environment, because physical tension and stress can temporarily increase blood pressure. To find out whether it is constantly high, blood pressure measurements should be taken on several days and at different times of the day too.

Ways to lower blood pressure

There are different ways to permanently lower blood pressure enough so that the risk of complications is reduced. People are often advised to make lifestyle changes and do more exercise, drink less alcohol, stop smoking and manage their stress, for example. You can read about how losing weight can affect blood pressure here. Medication is often used too.

Dietary changes are an important part of changes in everyday life. One approach is to eat less salt. Research has shown that people who have more salt in their diet have higher blood pressure too. There is a lot of salt in processed foods, such as

• convenience foods,
• chips and salty snacks,
• many types of cheese,
• canned fish,
• cured and smoked meats, and
• bread.

It can also be a good idea to see how much salt there is in the mineral water you drink, as this can vary quite a lot.

Fresh and unprocessed foods are particularly low in salt. Examples include

• fruit and vegetables,
• fish,
• meat, and
• dairy products like yoghurt.

People who want to reduce their salt intake can do so by eating less salty foods and using less salt to season their food. But we cannot cut salt out of our diets completely: we need a certain amount of salt to live. Because many food products have small amounts of salt in them, however, reducing your salt intake is not likely to lead to a salt deficiency.

Research on salt reduction

The German Institute for Quality and Efficiency in Health Care (IQWiG), the publisher of this website, was commissioned by the German Federal Joint Committee (G-BA) to look at the effect of low-salt diets in people who have high blood pressure. The G-BA is the national decision-making body of the German healthcare system, including the health insurance funds, hospitals, community-based doctors, dentists and psychotherapists. IQWiG worked on the report together with researchers from the Graz University Hospital in Austria.

In order to find out whether reducing the amount of salt in your diet has benefits, the researchers looked for systematic reviews. These reviews analyze trials on a particular topic and summarize their outcomes. In this case the researchers were interested in trials that compared the following groups of patients: one group that was supposed to reduce their salt intake for a longer period of time and one group that did not aim to do this.

For people who do things to lower their blood pressure it is particularly important that this will help lower their risk of complications like heart attacks and strokes in the long term. Because of this, the researchers analyzed the reviews with a focus on whether low-salt diets were able to prevent complications and deaths, and how they affected quality of life. They also looked at how people’s blood pressure changed over time and whether it meant they needed less medication for their blood pressure.

Low-salt diet reduces blood pressure

The researchers found 7 good-quality reviews including a total of 62 individual trials. But the trials did not provide a clear answer to the important question of how reducing your salt intake affects the risk of cardiovascular disease and related deaths. Most of the trials only lasted a few months, but complications usually only arise after several years. So the long-term effects of reducing your salt intake are still not clear.

However, the trials consistently showed that going on a low-salt diet can lower blood pressure. On average, the participants’ systolic blood pressure dropped by 3.6 to 8 mm Hg and their diastolic blood pressure dropped by 2 to 3 mm Hg. This is roughly the same effect that can be achieved by losing weight. It is a big enough reduction to have a significant effect on the treatment.

But how much do you have to reduce your salt intake to lower your blood pressure that much? One review calculated that eating 6 grams of salt less per day reduced participants’ systolic blood pressure by about 7 mm Hg and their diastolic pressure by almost 4 mm Hg. That is the equivalent of about one teaspoon of salt. In everyday life, these values can vary from person to person, though, so it is not possible to say exactly how much you should reduce your salt intake to achieve a certain reduction in blood pressure. It is not always easy to stick to a low-salt diet in the long term. But reducing your salt intake by even a small amount can already help lower your blood pressure.

These results mainly apply to people who are not taking any blood-pressure-lowering (antihypertensive) medication. Based on the trial data, it is not possible to say whether combining both medication and a low-salt diet leads to a greater reduction in blood pressure than taking medication alone. There was also hardly any data on whether people who reduce their salt intake need less blood-pressure-lowering medication, or can even stop taking it altogether.

The trials did not provide any information about how this dietary change affected people’s quality of life. There were also hardly any data on adverse effects: only one trial reported that people who reduced their salt intake were somewhat more likely to have muscle cramps. Another trial found, however, that people who were on a low-salt diet had fewer headaches.

It is not yet possible to say how long the health effects of low-salt diets last. Does the blood pressure remain lower over the years? And can they help prevent complications? These questions remain unanswered. Still: reducing your salt intake can help lower your blood pressure in the medium term. So if you have high blood pressure, it can be a good idea to eat fresh meat rather than smoked meat, or an apple rather than salted peanuts.

Author: Institute for Quality and Efficiency in Health Care (IQWiG)

Note

This health information is a summary of a scientific report published by IQWiG. It is not an assessment of the right to have health care services reimbursed by statutory health insurance funds in Germany. By law, decisions about the reimbursement of diagnostic and therapeutic procedures can only be made by the German Federal Joint Committee (G-BA). The Federal Joint Committee takes IQWiG reports into consideration in its decision-making process. You can find information about the decisions of the German Federal Joint Committee on its English-language website, www.english.g-ba.de.

© IQWiG (Institute for Quality and Efficiency in Health Care)