Frequently adding salt to food ups risk of mortality, lower life expectancy

The frequent addition of salt to foods has been found to be associated with a higher risk of all-cause premature mortality and lower life expectancy, a prospective UK study has shown.

“Adding salt to foods (usually at the table) is a common eating behaviour directly related to an individual’s long-term preference to salty foods and habitual salt intake,” said the researchers. In the Western diet, adding salt at the table accounts for up to 20 percent of total salt intake. [J Am Coll Nutr 1991;10:383-393; Br J Nutr 2013;110:552-558]

“Our study provides novel evidence to show the adverse relation between sodium intake and mortality,” said the researchers. “[We found that] a higher frequency of adding salt to foods was significantly associated with a higher hazard of premature mortality and lower life expectancy, independent of diet, lifestyle, socioeconomic level, and pre-existing diseases.”

The main analysis included >500,000 participants from the UK Biobank study (mean age 56 years, 54 percent female). When asked whether they add salt to their foods (not including salt used in cooking), participants were to select one answer from five choices: never/rarely, sometimes, usually, always, and prefer not to answer. [Eur Heart J 2022;43:2878-2888]

A total of 18,474 premature deaths were reported during a median follow-up of 9 years.

As the frequency of adding salt to foods increased, so did the hazard of all-cause premature mortality, after adjusting for multiple* covariates (adjusted hazard ratios, 1.0, 1.02, 1.07, and 1.28 for the respective ‘never/rarely’, ‘sometimes’, ‘usually’, and ‘always’ groups (p_trend=0.001). There were no appreciable changes in the results after further adjustments** or exclusions***.

This positive association seemed to be attenuated with increased intake of potassium-rich foods such as fruits and vegetables (p_interaction=0.02). “[This finding lends] support to the hypothesis that a high potassium intake can attenuate the adverse associations of high-sodium intake with health outcomes,” the researchers explained.

When evaluating for cause-specific premature mortality, a significant association was observed between higher frequency of adding salt to foods and higher risk of cardiovascular (CVD) and cancer mortality (p_trend<0.001 for both). “[This] indicates that the increased hazard of all-cause mortality associated with more frequent addition of salt to foods could be partly attributed to CVD and cancer-specific mortality,” they said.

Furthermore, life expectancy at age 50 years was lower in women by an average of 1.5 years, more so among men (about 2.3 years lower), who reported always adding salt to foods as opposed to those who never/rarely did. At age 60 years, the corresponding drops in years of life expectancy were 1.4 and 2.0 years in women and men, respectively.

A modest reduction could go a long way

“[W]e provided a unique perspective to evaluate the association between salt usage behaviours and mortality,” said the researchers. “The frequency of adding salt to foods … is less likely to be affected by the large day-to-day variations in sodium intake [and] is easily assessed in clinical and public settings.”

Considering that most of the salt intake in the Western diet comes from processed foods, the findings could be useful for dietary interventions and may help guide recommendations on behavioural modifications about salt intake.

“Our findings 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 concluded, calling for further trials to corroborate the findings.