A systematic review and meta-analysis of 13 studies published in the BMJ has found that a high level of dietary salt is associated with a significantly increased risk of stroke and total cardiovascular disease.
Researchers from Coventry and Naples, Italy, extracted and pooled results from relevant studies published between 1966 and 2008. To be included in the analysis, studies had to be an adult population study, to assess salt intake as baseline exposure, to determine either stroke or total cardiovascular disease prospectively as the outcome, to follow participants for at least three years, and to indicate the number of participants exposed and the rate or number of events across different categories of salt intake.
The 19 independent cohort samples examined by these studies included 177,025 men and women, from the US, Finland, Japan, Scotland, Taiwan and the Netherlands; they experienced 5346 strokes and 5161 total cardiovascular disease events between them.
The authors found, having excluded the possibility of publication bias, that higher salt intake was associated with a 23% greater risk of stroke and a 14% higher risk of cardiovascular disease. They say that: “This meta-analysis shows unequivocally that higher salt intake is associated with a greater incidence of strokes and total cardiovascular disease … The pooled relative risk indicates a 23% greater risk of stroke for an average difference in sodium intake (weighted for the population size of each study) of 86mmol, equivalent to about 5g of salt a day.”
The authors add: “It is reasonable to expect considerable benefit on the rate of cardiovascular disease from a reduction in salt intake,” and conclude: “One barrier to a more effective implementation of public health policies has been the historical opposition of the food industry, based on the arguments that the available evidence does not show significant benefits on hard endpoints at a population level from a moderate reduction in salt intake. Our study now clearly addresses these doubts.”