People who add extra salt to their meals at the table are at higher risk of premature death from any cause, according to a study of more than 500,000 people published in European Heart Journal today (Monday).
Compared to those who never or rarely added salt, those who always added salt to their food had a 28% increased risk of premature death. In the general population, about three in every hundred people between the ages of 40 and 69 die prematurely. The increased risk of always adding salt to food seen in the current study suggests that another one in every hundred may die prematurely in this age group.
In addition, the study found lower life expectancy among people who always added salt compared to those who never or rarely added salt. At age 50, 1.5 years and 2.28 years were reduced in life expectancy for women and men, respectively, who always added salt to their food compared to those who never or rarely did.
The researchers, led by Professor Lu Qi of the Tulane University School of Public Health and Tropical Medicine, New Orleans, US, say their findings have several implications for public health.
“To my knowledge, our study is the first to assess the relationship between added salt to foods and premature death,” he said. “This provides new evidence to support recommendations for changing dietary behavior to improve health.” Even modest reductions in sodium intake, by adding less or no salt to food at the table, are likely to produce significant health benefits, especially when achieved in the general population.”
Estimating total sodium intake is extremely difficult because many foods, especially pre-prepared and processed foods, have high levels of added salt before they even reach the table. Studies assessing salt intake through urine tests often take only one urine test and therefore do not necessarily reflect usual behavior. In addition, foods high in salt are often accompanied by foods rich in potassium, such as fruits and vegetables, which is good for us . Potassium is known to protect against the risk of heart disease and metabolic diseases such as diabetes, while sodium increases the risk of conditions such as cancer, high blood pressure and stroke.
For these reasons, the researchers chose to look at whether people add salt to their food at the table, regardless of the salt added during cooking.
“Adding salt to table foods is a common eating behavior that is directly related to an individual’s long-term preference for salty-tasting foods and habitual salt intake,” said Prof Chi. “In the Western diet, added table salt accounts for 6-20% of total salt intake and provides a unique way to assess the relationship between habitual sodium intake and risk of death.”
The researchers analyzed data from 501,379 people taking part in the UK Biobank study. When they joined the study between 2006 and 2010, participants were asked via a touchscreen questionnaire whether they added salt to their foods (i) never/rarely, (ii) sometimes, (iii) usually, (iv) always, or ( v) prefer not to answer. Those who chose not to answer were not included in the analysis. The researchers adjusted their analyzes to take into account factors that could affect the results, such as age, sex, race, deprivation, body mass index (BMI), smoking, alcohol intake, physical activity, diet and medical conditions such as diabetes, cancer and diseases of the heart and blood vessels. They followed the participants for an average (mean) of nine years. Premature death is defined as death before the age of 75.
In addition to finding that always adding salt to foods was associated with a higher risk of premature death from all causes and a reduction in life expectancy, the researchers found that these risks tended to decrease slightly in people who consumed the highest amounts fruits and vegetables, although these results were not statistically significant.
“We were not surprised by this finding as fruits and vegetables are major sources of potassium, which has a protective effect and is associated with a lower risk of premature death,” said Prof Chi.
He added: “As our study is the first to report an association between added salt in foods and mortality, further studies are needed to confirm the findings before recommendations can be made.”
In an editorial to accompany the article Professor Annika Rosengren, senior researcher and professor of medicine at the Sahlgrenska Academy, University of Gothenburg, Sweden, who was not involved in the study, writes that the net effect of drastically reducing people’s salt intake remains controversial.
“Given the various indications that very low sodium intake may not be beneficial or even harmful, it is important to distinguish between individual-based recommendations and population-level actions,” she wrote.
She concludes: “Classical epidemiology argues that greater net benefit is achieved by a whole-population approach (achieving a small effect in many people) than by targeting high-risk individuals (a large effect but achieved in only a small number of people ) The obvious and evidence-based strategy for preventing cardiovascular disease in individuals is early detection and treatment of hypertension, including lifestyle changes, while community-level salt reduction strategies will lower mean blood pressure levels among population, which will result in fewer people developing hypertension, needing treatment, and becoming ill. Not adding extra salt to food is unlikely to be harmful and may contribute to strategies to lower blood pressure levels in the population.”
A strength of Prof. Qi’s study is the large number of people involved. There are also some limitations, which include: the possibility that added salt to food is an indication of unhealthy lifestyle and lower socioeconomic status, although the analyzes attempted to adjust for this; there was no information on the amount of salt added; salt intake may be related to total energy intake and intermingled with intake of other foods; participation in the UK Biobank is voluntary and therefore the results are not representative of the general population, so further studies are needed to confirm the findings in other populations.
Prof. Qi and his colleagues will conduct further studies on the relationship between the addition of salt to foods and various chronic diseases such as cardiovascular disease and diabetes. They also await potential clinical trials to test the effects of reducing salt intake on health outcomes.
 An example of a typically salty food that also contains vegetables is tacos, which are often filled with beans and vegetables.
 “Salt – The Sweet Spot?”, by Annika Rosengren. European Heart Journal. doi:10.1093/eurheartj/ehac336