Adding Salt to Food Linked to Higher Risk of Premature Death

July 11, 2022

Adding salt to food at the table was linked to a higher risk of premature death and a lower life expectancy, independent of diet, lifestyle, socioeconomic level, and pre-existing diseases, in a new study.

In the study of more than 500,000 people, compared with those who never or rarely added salt, those who always added salt to their food had a 28% increased risk of dying prematurely (defined as death before the age of 75 years).

Results also showed that adding salt to food was linked to a lower life expectancy. At the age of 50 years, life expectancy was reduced by 1.5 years in women and by 2.28 years in men who always added salt to their food compared with those who never, or rarely, did.

However, these increased risks appeared to be attenuated with increasing intakes of high-potassium foods (vegetables and fruits).

The study was published online in the European Heart Journal on July 10.

“As far as we are aware, this is the first study to analyze adding salt to meals as a unique measurement for dietary sodium intake. Such a measure is less likely affected by other dietary components, especially potassium intake,” senior author, Lu Qi, MD, Tulane University School of Public Health and Tropical Medicine, New Orleans, Louisiana, told | Medscape Cardiology.

“Our study provides supportive evidence from a novel perspective to show the adverse effects of high sodium intake on human health, which is still a controversial topic. Our findings support the advice that reduction of salt intake by reducing the salt added to meals may benefit health and improve life expectancy. Our results also suggest that high intakes of fruits and vegetables are beneficial regarding lowering the adverse effects of salt,” he added.

Link Between Dietary Salt and Health Is Subject of Longstanding Debate

In the paper the researchers explain that the relationship between dietary salt intake and health remains a subject of longstanding debate, with previous studies on the association between sodium intake and mortality having shown conflicting results.

They attribute the inconsistent results to the low accuracy of sodium measurement, noting that sodium intake varies widely from day to day, but the majority of previous studies have largely relied on a single day’s urine collection or dietary survey for estimating the sodium intake, which is inadequate to assess an individual’s usual consumption levels.

They also point out that it is difficult to separate the contributions of intakes of sodium and potassium to health based on current methods for measuring dietary sodium and  potassium, and this may confound the association between sodium intake and health outcomes.

They note that the hypothesis that a high-potassium intake may attenuate the adverse association of high-sodium intake with health outcomes has been proposed for many years, but studies assessing the interaction between sodium intake and potassium intake on the risk of mortality are scarce.

Adding salt to food at the table is a common eating behavior directly related to an individual’s long-term preference for salty tasting foods and habitual salt intake, the authors say, adding that commonly used table salt contains 97%–99% sodium chloride, minimizing the potential confounding effects of other dietary factors including potassium.

“Therefore, adding salt to foods provides a unique assessment to evaluate the association between habitual sodium intake and mortality.”

UK Biobank Study

For the current study Qi and colleagues analyzed data from 501,379 people taking part in the UK Biobank study. When joining the study between 2006 and 2010, the participants were asked whether they added salt to their foods never/rarely, sometimes, usually or always. Participants were then followed for a median of 9 years.

After adjustment for sex, age, race, smoking, moderate drinking, body mass index, physical activity, Townsend deprivation index, high cholesterol, chronic kidney disease, diabetes, cardiovascular disease, and cancer, results showed an increasing risk of all-cause premature mortality rose with increasing frequency of adding salt to foods.

The adjusted hazard ratios compared with those who never or rarely added salt were 1.02 (95% CI, 0.99–1.06) for those who added salt sometimes, 1.07 (1.02–1.11) for those who usually added salt, and 1.28 (1.20–1.35) for those who always added salt.

The researchers also estimated the lower survival time due to the high frequency of adding salt to foods. At age 50, women who always added salt to foods had an average 1.50 fewer years of life expectancy, and men who always added salt had an average 2.28 fewer years of life expectancy, as compared with their counterparts who never/rarely added salt to foods.

For cause-specific premature mortality, results showed that higher frequency of adding salt to foods was significantly associated with a higher risk of cardiovascular mortality and cancer mortality, but not for dementia mortality or respiratory mortality. For the subtypes of cardiovascular mortality, adding salt to foods was significantly associated with higher risk of stroke mortality but not coronary heart disease mortality.

Other analyses suggested that the association of adding salt to foods with an increased risk of premature mortality appeared to be attenuated with increasing intake of food high in potassium (fruits and vegetables).

The authors point out that the amounts of discretionary sodium intake (the salt used at the table or in home cooking) have been largely overlooked in previous studies, even though adding salt to foods accounts for a considerable proportion of total sodium intake (6%–20%) in western diets.

“Our findings also support the notion that even a modest reduction in sodium intake is likely to result in substantial health benefits, especially when it is achieved in the general population,” they conclude.

Conflicting Information From Different Studies

But the current findings seem to directly contradict those from another recent study by Messerli et al showing higher sodium intake correlates with improved life expectancy.

Addressing these contradictory results, Qi commented: “The study of Messerli et al is based on an ecological design, in which the analysis is performed on country average sodium intake, rather than at the individual level. This type of ecological study has several major limitations, such as the lack of individuals' sodium intake, uncontrolled confounding, and the cross-sectional nature. Typically, ecological studies are not considered useful for testing hypothesis in epidemiological studies.”

Qi noted that, in contrast, his current study analyzes individuals' exposure, and has a prospective design. “Our findings are supported by previous large-scale observational studies and clinical trials which show the high intake of sodium may adversely affect chronic diseases such as cardiovascular disease and hypertension,” he added.

Lead author of the ecological study, Franz Messerli, MD, Bern University Hospital, Switzerland, however, is not convinced by the findings from Qi’s study.

“The difference in 24-hour sodium intake between those who never/rarely added salt and those who always did is a minuscule 0.17g. It is highly unlikely that such negligible quantity has any impact on blood pressure, not to mention cardiovascular mortality or life expectancy,” he commented to | Medscape Cardiology.

He also pointed out that in Qi’s study, people who added salt more frequently also consumed more red meat, processed meat, less fish, and less fruit and vegetables. “I would suggest that the bad habit of adding salt at the table is simply a powerful marker for an unhealthy diet.”

“There is no question that an excessive salt intake is harmful in hypertensive patients and increases the risk of stroke. But 0.17g is not going to make any difference,” Messerli added.

What Is the Optimum Level?

In an editorial accompanying the current publication in the European Heart Journal,  Annika Rosengren, Sahlgrenska University Hospital, Gothenburg, Sweden, notes that  guidelines recommend a salt intake below 5g, or about a teaspoon, per day. But few individuals meet this recommendation.

Because several recent studies show a U- or J-shaped association between salt and atherosclerotic cardiovascular disease, reducing salt intake across the whole population may not be universally beneficial, Rosengren says.

“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,” she writes.

Instead, she advises a diet rich in fruit and vegetables should be a priority to counterbalance potentially harmful effects of salt, and for many other reasons.

And she adds that people at high risk, such as those with hypertension who have a high salt intake, are probably well advised to cut down, and not adding extra salt to already prepared foods is one way of achieving this. However, at the individual level, the optimal salt consumption range, or the ‘sweet spot’ remains to be determined. 

“Not adding extra salt to food is unlikely to be harmful and could contribute to strategies to lower population blood pressure levels,” Rosengren concludes.

European Heart Journal. Published online July 10, 2022. Full text; Editorial.

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