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More generous use of salt outside cooking was associated with premature mortality -- but not in people eating more potassium rich-foods such as vegetables and fruits -- according to a study of over half a million people.

Participants from the U.K. Biobank reported their frequency of table salt use, with higher use linked to a rising risk of all-cause mortality over a median 9.0 years of follow-up (P<0.001 for trend):

• Never: adjusted HR 1.00 (reference)
• Sometimes: adjusted HR 1.02 (95% CI 0.99-1.06)
• Usually: adjusted HR 1.07 (95% CI 1.02-1.11)
• Always: adjusted HR 1.28 (95% CI 1.20-1.35)

A high frequency of adding salt to foods was significantly associated with cardiovascular disease mortality (namely strokes, not coronary heart disease mortality), as well as cancer mortality, reported nutritional epidemiologist Lu Qi, MD, PhD, of Tulane University in New Orleans and Harvard T.H. Chan School of Public Health in Boston, and colleagues.

In contrast, there was no increase in dementia mortality, nor respiratory mortality, with more table salt use, Qi's group noted in the .

"Notably, previous studies investigating the association between sodium intake and risk of mortality have produced conflicting results, showing positively linear, J-shaped, or inversely linear associations," the study authors wrote.

Their focus on sodium added at the table provides another look at the relationship between salt and clinical outcomes.

"Adding salt to foods (usually at the table) is a common eating behavior directly related to an individual's long-term preference to salty taste foods and habitual salt intake. Indeed, in western diet, adding salt at the table accounts for 6-20% of total salt intake. In addition, the commonly used table salt contains 97-99% sodium chloride, minimizing the potential confounding effects of other dietary factors including potassium," they noted.

Indeed, there was an interaction by intake of fruits and vegetables, such that the table salt-mortality relationship was no longer significant in those commonly eating these potassium-rich foods.

"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. Instead, to counterbalance potentially harmful effects of salt, and for many other reasons, a diet rich in fruit and vegetables should be a priority on the individual, as well as the population, level," wrote cardiologist Annika Rosengren, MD, PhD, of the University of Gothenburg and Sahlgrenska University Hospital in Sweden, in an .

"People at high risk with 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," she added.

This population-based cohort study included 501,379 people, all volunteers recruited to the U.K. Biobank from 2006 to 2010. Mean age was 56.5 years, and 45.6% were men.

Participants answered questionnaires on the frequency of adding table salt to food, in addition to providing urine samples and food diaries.

A higher frequency of adding salt to foods correlated with higher concentrations of spot urinary sodium and estimated 24-hour sodium excretion, Qi and colleagues found.

There were 18,474 premature deaths recorded over follow-up.

Residual confounding potentially affected the study results, even with the statistical adjustments by the authors. Moreover, the findings are of questionable generalizability to other populations.

"Still, at the population level, there is no reason to be complacent about salt intake. There is a well-established link between salt consumption and population blood pressure levels," Rosengren maintained.

"Not adding extra salt to food is unlikely to be harmful and could contribute to strategies to lower population blood pressure levels," she concluded.

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