Intake of salt is a biological necessity, inextricably woven into physiologic systems. However, excessive salt intake is associated with high blood pressure. Hypertension is linked to increased cardiovascular morbidity and mortality, and it is estimated that excessive salt intake causes approximately 5 million deaths per year worldwide. Reducing salt intake lowers blood pressure, but processed foods contain “hidden” salt, which makes dietary control of salt difficult. This problem is compounded by growing inequalities in food systems, which present another hurdle to sustaining individual dietary control of salt intake.
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Of the 87 risk factors included in the Global Burden of Diseases, Injuries, and Risk Factors Study 2019, high systolic blood pressure was identified as the leading risk factor for disease burden at the global level and for its effect on human health. A range of strategies, including primary care management and reduction in sodium intake, are known to reduce the burden of this critical risk factor. Two questions remain unanswered:
Cardiovascular disease and death
Because dietary sodium intake has been identified as a risk factor for cardiovascular disease and premature death, high sodium intake can be expected to curtail life span. A study tested this hypothesis by analyzing the relationship between sodium intake and life expectancy and survival in 181 countries. Sodium intake correlated positively with life expectancy and inversely with all-cause mortality worldwide and in high-income countries, which argues against dietary sodium intake curtailing life span or a being risk factor for premature death. These results help fuel a scientific debate about sodium intake, life expectancy, and mortality. The debate requires interpreting composite data of positive linear, J-shaped, or inverse linear correlations, which underscores the uncertainty regarding this issue.
In a prospective study of 501,379 participants from the UK Biobank, researchers found that higher frequency of adding salt to foods was significantly associated with a higher risk of premature mortality and lower life expectancy independently of diet, lifestyle, socioeconomic level, and preexisting diseases. They found that the positive association appeared to be attenuated with increasing intake of high-potassium foods (vegetables and fruits).
In addition, the researchers made the following observations:
- For cause-specific premature mortality, they found that higher frequency of adding salt to foods was significantly associated with a higher risk of cardiovascular disease mortality and cancer mortality (P-trend < .001 and P-trend < .001, respectively).
- Always adding salt to foods was associated with the lower life expectancy at the age of 50 years by 1.50 (95% confidence interval, 0.72-2.30) and 2.28 (95% CI, 1.66-2.90) years for women and men, respectively, compared with participants who never or rarely added salt to foods.
The researchers noted that adding salt to foods (usually at the table) is common and is directly related to an individual’s long-term preference for salty foods and habitual salt intake. Indeed, in the Western diet, adding salt at the table accounts for 6%-20% of total salt intake. In addition, 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 way to evaluate the association between habitual sodium intake and mortality – something that is relevant, given that it has been estimated that in 2010, a total of 1.65 million deaths from cardiovascular causes were attributable to consumption of more than 2.0 g of sodium per day.