Can adding extra salt to food cut your life expectancy?

People who always add salt to their food after cooking are 28 per cent more likely to be at risk of an early death, when compared to those who never or rarely use extra salt on meals, according to new research published in the European Heart Journal.

The study also found a link between those who always add extra salt to foods and a lower life expectancy at age 50 – 1.5 years lower for women and just over 2 years lower for men.

The researchers also found that eating lots of high-potassium foods, such as fruit and vegetables, may help to reduce this increased risk of an early death.

For this study, researchers used results from a questionnaire by UK Biobank – a research database which contains medical information from over 500,000 volunteers – to find out if and how often people are adding salt to their food after cooking.

Overall, the study claims that its findings show “even a modest reduction” in salt is likely to provide health benefits.

The BHF verdict - is adding salt to food healthy?

So, can you eat too much salt? Chloe MacArthur, Senior Cardiac Nurse at the British Heart Foundation, said: “We need some salt in our diet, but eating too much – as most of us do - may lead to high blood pressure, which in turn raises the risk of heart attack and stroke.

“This study looks at people who add salt to food as a way of measuring salt intake, not because salt we add at the table is any worse than the salt that is already in our food. It is usually better to avoid adding salt to food if you can – but the vast majority of salt is already in food before we buy it, which means we are consuming more than we realise.

• Get advice on how to reduce the amount of salt you use, as well as other healthy eating tips, in our nutrition section

How good was the research?

This study used a simple question about whether people add salt to their food, to give an indication of preference for salt.

The study says, “in [the] western diet, adding salt at the table accounts for 6–20 per cent of total salt intake". While this isn’t the major source of salt in our diets, the researchers add that a taste for salty food, indicated by the addition of salt at the table, will translate to eating more salty food generally and so could be a good way of assessing longer term salt intake.

They found that people who added salt (sodium chloride) to food also had more sodium in their urine, based on spot checks taken randomly (which was viewed as an indication that they may be consuming more salt).

This type of study can only show a link, not cause and effect, so we can’t say that adding salt to food is a cause of early death. It’s also a new approach to assessing the connection between salt and health, which would need to be repeated to know how reliable it is. There are also some limitations to it. For example, we know that salt added at the table can be added out of habit rather than taste preference.

There are also different ways that people can be adding salt to their food other than by adding table salt, such as with cheese, sauces or pickles. Salt added during cooking was also not included in the measurements but could be contributing to the total amount eaten.

We also know from reformulation programmes (which are efforts by manufacturers to change the recipes of food and drink products to make them healthier), that these can be effective in significantly reducing the amount of salt in our diets over time without us noticing a change in taste or having to change our habits.

Participants were recruited between 2006 and 2010, and their health was monitored for an average of nine years. During this time, nearly 18,500 early deaths were recorded.

Strengths of the study include that it is based on information provided by a reliable source and uses a large sample-size from across the British population.

Researchers left out participants whose questionnaire answers about seasoning with salt were incomplete. They also used 24-hour dietary recalls, as well as random urine samples from some of the participants, to account for daily dietary differences and help deal with the challenges involved in measuring salt intake.

The researchers adjusted the results to take account of factors that could have affected the results, including weight and physical activity.

The study authors note that eating too much salt in food could also simply be an indicator of an unhealthy lifestyle in general. Although the findings took lifestyle factors into account, it’s possible they could still have had an effect on the results.

The authors also mention previous studies, which show both positive and negative links between salt intake, death, and life expectancy – so there is still some debate in this area.

Weaknesses of the study include that all participants were based in the UK and aged between 40 and 69, as well as being volunteers. This means the results do not necessarily represent the whole population.

How good was the media coverage?

Coverage of this study in the media included articles by the Guardian, the Daily Express, and Sky News.

None of the reports provide a link to the original research, but both the Daily Express and Sky News do quote the BHF view on the risks of eating too much salt.

The Guardian takes an in-depth look at the study, as well as its strengths and weaknesses, and – importantly – highlights that the link to an earlier death specifically relates to those who “always” add salt to meals after cooking.

The newspaper’s coverage helpfully includes quotes from one of the researchers, as well as adding further opinion from an academic who was not involved in the work. This opinion, from Professor Annika Rosengren, seems to have been lifted from an editorial in the European Heart Journal. That editorial refers to a range of evidence about salt, including some on the health risks of too little salt.

The Guardian quoted the sentence: “So far, what the collective evidence about salt seems to indicate is that healthy people consuming what constitutes normal levels of ordinary salt need not worry too much about their salt intake.” This is not necessarily helpful, without a definition of “normal levels of ordinary salt”, and may not be true, given that we know that most people in the UK eat well above the recommended maximum levels of salt.

The sentence was quoted without the conclusion that the writer comes to in the same editorial, which is: “Not adding extra salt to food is unlikely to be harmful and could contribute to strategies to lower population blood pressure levels.”

More helpfully, the Guardian does mention that those at high risk of heart disease “should probably cut down” on the amount of salt they use.

Coverage from the Daily Express lacks detail and features only three paragraphs of information. It leads with the headline that “adding salt to food ‘increases risk of dying early’,” without making it clear that the study only looked at adding salt after cooking.

Sky News also leads with a similar headline but does make it clear several times that the study focuses on the impact of extra salt. Sky also quotes one of the study’s researchers, including noting that “further studies are needed to validate the findings before making recommendations."

Both the Daily Express and Sky News say that one extra person in every 100 could die earlier, due to adding too much salt to food. However, to provide context, the Sky News report also mentions that typically, “around three in 100 people aged 40 to 69 die early across the general population”.

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