Is it generally believed that excessive salt consumption is detrimental to human health.
In the UK, for example, it is estimated that if people were to reduce their daily intake from 8.1g to the recommended 6g per day, it would reduce the number of strokes by 22% and heart attacks by 16%.
However, the negative impacts of salt consumption on health were recently cast into doubt when a team of international researchers studied sodium intake, life expectancy, and all-cause mortality.
Published in the European Heart Journal, the study tested the hypothesis that a high sodium intake can be expected to curtail lifespan. What they found was, in fact, the opposite: that sodium intake correlated positively with life expectancy and inversely with all-cause mortality worldwide.
In the face of two opposing arguments, researchers in Switzerland and the US have sought to better understand the impact of salt on dietary health. In particular, the team has homed in on table salt, asking: is premature mortality and life expectancy linked to how often one adds salt to food?
Adding salt to foods
Adding salt to foods is a common practice in western countries and is directly related to an individual’s long-term preference for salty-tasting foods and habitual salt intake.
“In the Western diet, adding salt at the table accounts for 6-20% for the total salt intake and provides a unique way to evaluate the association between habitual sodium intake and the risk of death,” said research lead Professor Lu Qui, of Tulane University School of Public Health and Tropical Medicine, New Orleans, US.
To investigate whether this practice has an impact on all-cause premature mortality and lower life expectancy, the researchers analysed 501,379 participants from UK biobank who completed the questionnaire on the frequency of adding salt to foods at baseline.
Information on death and death date was obtained by reviewing death certificates across England, Wales and Scotland.
The study – also published in the European Heart Journal - found that people who add extra salt to their food at the table are at a higher risk of dying prematurely from any cause.
Compared to those who never or rarely added salt, those who always added salt to their food had a 28% increased risk of dying prematurely.
In the general population, about three in every hundred people aged between 40 and 69 die prematurely. The increased risk from always adding salt to food seen in the study suggests that one more person in every hundred may die prematurely in this age group.
Further, the researchers found a lower life expectancy among people who always added salt compared to those who never, or rarely added salt. At the age of 50, 1.5 years and 2.28 years were reduced from the life expectancy of women and men, respectively, who always added salt to those food compared to those who never or rarely did.
“To my knowledge, our study is the first to assess the relation between adding salt to foods and premature death,” said Prof Qi.
“It provides novel evidence to support recommendations to modify eating behaviours for improving health. Even a modest reduction in sodium intake, by adding less or no salt to food at the table, is likely to result in substantial health benefits, especially when it is achieved in the general population.”
The potassium factor
The researchers also noted that consumers who ate the highest amounts of fruits and vegetables tended who have slightly reduced risk of premature death and reduction in life expectancy.
“We were not surprised by this finding as fruits and vegetables are major sources of potassium, which has protective effects and is associated with a lower risk of premature death,” said Prof Qui.
“Because our study is the first to report a relation between adding salt to foods and mortality, further studies are needed to validate the findings before making recommendations.”
Previous research has, however, linked potassium intake and sodium reduction with health benefits.
Last year, a study published in the New England Journal of Medicine, analysed participants from 600 villages in rural China Participants either used a salt substitute made up of 75% sodium chloride and 25% potassium, or continued to use regular table salt for an average period of 4.5 and 5 years.
Findings revealed that compared to the control group, the rates of stroke, major cardiovascular events, and death were lower in participants that consumed the sodium chloride and potassium salt substitute.
“This is quite simply the single most worthwhile piece of research I’ve ever ben involved with,” said lead investigator Professor Bruce Neal of The George Institute for Global Health at the time.
“Switching from table salt to salt substitute is a highly feasible and low-cost opportunity to have a massive global health benefit.”
Study co-author Feng He, Professor of Global Health Research at the Wolfson Institute of Population Health, Queen Mary University of London, similarly stressed the potential significance of the findings.
“Globally, millions of lives would be saved by this simple approach. Salt consumption in China is amongst the highest in the world, with average salt intakes (10-12g/day) more than double the WHO recommended limit (less than 5g/day).
“In China and most developing countries, the majority of salt in the diet is added by the consumer, therefore encouraging people to use less during cooking is the best strategy to improve public health.”
European Heart Journal
‘Sodium intake, life expectancy, and all-cause mortality’
Published 20 December 2020
Authors: Franz H Messerli, Louis Hofstetter, Lamprini Syrogiannouli, Emrush Rexhaj, George C M Siontis, Christian Seiler, Sripal Bangalore.
European Heart Journal
‘Adding salt to foods and hazard of premature mortality’
Published 10 July 2022
Authors: Hao Ma, Qiaochu Xue, Xuan Wang, Xiang Li, Oscar H Franco, Yanping Li, Yoriko Heianza, JoAnn E Manson, Lu Qi.
The New England Journal of Medicine
‘Effect of Salt Substitution on Cardiovascular Events and Death’
Published 29 August 2021
Authors: Bruce Neal, Yangfeng Wu, Xiangxian Feng, Ruijuan Zhang, Yuhong Zhang, Jimpgu Shi, Jianxin Zhang, Maoyi Tian, Liping Huang, Zhifang Li, Yan Yu, Yi Zhao et al.